Thursday, 19 July 2012

The Experiments of R.P. Williams 1888

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The experiments from
An Introduction to Chemical Science by R.P. Williams 1888.

The experiments begin rather lamely, however things start getting interesting around experiment 23. A warning about laughing gas is given in experiment 67.  Experiment 116 - "the gas in the flask is the most poisonous known, and a single bubble of it inhaled is said to have killed the discoverer."  The drinker will be mortified by experiment 132.

Note - from the Gutenburg .txt file, therefore no diagrams and watch out for errors in formulae.

Experiment 1.--Note the length of 10 cm. (centimeters) on a metric ruler, as shown in Figure 1. Estimate by the eye alone this distance on the cover of a book, and then verify the result. Do the same on a test-tube. Try this several times on different objects till you can carry in mind a tolerably accurate idea of 10 cm. About how many inches is it? In the same way estimate the length of 1 cm, verifying each result. How does this compare with the distance between two blue lines of foolscap? Measure the diameter of the old nickel five- cent piece. Next, try in the same way 5 cm. Carry each result in mind, taking such notes as may be necessary.

Experiment 2.--Into a graduate, shown in Figure 2, holding 25 or 50 cc. (cubic centimeters) put 10 cc. of water; then pour this into a test-tube Note, without marking, what proportion of the latter is filled; pour out the water, and again put into the test-tube the same quantity as nearly as can be estimated by the eye. Verify the result by pouring the water back into the graduate. Repeat several times until your estimate is quite accurate with a test-tube of given size. If you wish, try it with other sizes. Now estimate 1 cc. of a liquid in a similar way. Do the same with 5 cc. A cubic basin 10 cm on a side holds a liter. A liter contains 1,000 cc. If filled with water, it weighs, under standard conditions, 1,000 grams. Verify by measurement.

Experiment 3.--Put a small piece of paper on each pan of a pair of scales. On one place a 10 g. (gram) weight. Balance this by placing fine salt on the other pan. Note the quantity as nearly as possible with the eye, then remove. Now put on the paper what you think is 10 g. of salt. Verify by weighing. Repeat, as before, several times. Weigh 1 g., and estimate as before. Can 1 g. of salt be piled on a one-cent coin? Experiment with 5 g.

Experiment 4.--Examine a few crystals of sugar, and crush them with the fingers. Grind them as fine as convenient, and examine with a lens. They are still capable of division. Put 3 g. of sugar into a test-tube, pour over it 5 cc. of water, shake well, boil for a minute, holding the test-tube obliquely in the flame, using for the purpose a pair of wooden nippers (Fig. 3). If the sugar does not disappear, add more water. When cool, touch a drop of the liquid to the tongue. Evidently the sugar remains, though in a state too finely divided to be seen. This is called a solution, the sugar is said to be soluble in water, and water to be a solvent of sugar. Now fold a filter paper, as in Figure 4, arrange it in a funnel (Fig. 5), and pour the solution upon it, catching what passes through, which is called the filtrate, in another test-tube that rests in a receiver (Fig. 5). After filtering, notice whether any residue is left on the filter paper. Taste a drop of the filtrate. Has sugar gone through the filter? If so, what do you infer of substances in solution passing through a filter? Save half the filtrate for Experiment 5, and dilute the other half with two or three times its own volume of water. Shake well, and taste. We might have diluted the sugar solution many times more, and still the sweet taste would have remained. Thus the small quantity of sugar would be distributed through the whole mass, and be very finely divided. By other experiments a much finer subdivision can be made. A solution of.00000002 g. of the red coloring matter, fuchsine, in 1 cc. of alcohol gives a distinct color.

Experiment 5.--Take the sugar solution saved from Experiment 4, and add slowly 4 cc.of strong sulphuric acid. Note any change of color, also the heat of the test-tube Add more acid if needed.

Experiment 6.--Mix, on a paper, 5 g. of iron turnings, and the same bulk of powdered sulphur, and transfer them to an ignition tube, a tube of hard glass for withstanding high temperatures. Hold the tube in the flame of a burner till the contents have become red-hot. After a minute break it by holding it under a jet of water. Put the contents into an evaporating-dish, and look for any uncombined iron or sulphur. Both iron and sulphur are elements. Is this an example of synthesis or of analysis? Why? Is the chemical union between masses of iron and sulphur, or between molecules, or between atoms? Is the product a compound, an element, or a mixture?

Experiment 7.--Try the same experiment, using copper instead of iron.

To Break Glass Tubing.
Experiment 8
.--Lay the tubing on a flat surface, and draw a sharp three-cornered file two or three times at right angles across it where it is to be broken, till a scratch is made. Take the tube in the hands, having the two thumbs nearly opposite the scratch, and the fingers on the other side. Press outward quickly with the thumbs, and at the same time pull the hands strongly apart, and the tubing should break squarely at the scratch. To break large tubing, or cut off bottles, lamp chimneys, etc., first make a scratch as before; then heat the handle of a file, or a blunt iron--in a blast-lamp flame by preference--till it is red-hot, and at once press it against the scratch till the glass begins to crack. The fracture can be led in any direction by keeping the iron just in front of it. Re-heat the iron as often as necessary.

To Make Ignition-Tubes.
Experiment 9
.--Hold the glass tubing between the thumb and forefinger of each hand, resting it against the second finger. Heat it in the upper flame, slowly at first, then strongly, but heat only a very small portion in length, and keep it in constant rotation with the right hand. Hold it steadily, and avoid twisting it as the glass softens. The yielding is detected by the yellow flame above the glass and by an uneven pressure on the hands. Pull it a little as it yields, then heat a part just at one side of the most softened portion. Rotate constantly without twisting, and soon it can be separated into two closed tubes. No thread should be attached; but if there be one, it can be broken off and the end welded. The bottom can be made more symmetrical by heating it red-hot, then blowing, gradually, into the open end, this being inserted in the mouth. The parts should be annealed by holding above the flame for a short time, to cool slowly. For hard glass--Bohemian--or large tubes, the blast-lamp or blowpipe is needed. In the blast-lamp air is forced out with illuminating gas. This gives a high degree of heat. Bulbs can be made in the same way as ignition-tubes, and thistle-tubes are made by blowing out the end of a heated bulb, and rounding it with charcoal.

To Bend Glass Tubing.
Experiment 10.
--Hold the tube in the upper flame. Rotate it so as to heat all parts equally, and let the flame spread over 3 or 4 cm. in length. When the glass begins to yield, without removing from the flame slowly bend it as desired. Avoid twisting, and be sure to have all parts in the same plane; also avoid bending too quickly, if you would have a well-rounded joint. Anneal each bend as made. Heated glass of any kind should never be brought in contact with a cool body. For making O, H, etc., a glass tube -- delivery-tube--50 cm. long should have three bends, as in Figure 6. The pupil should first experiment with short pieces of glass, 10 or 15 cm. long. An ordinary gas flame is the best for bending glass.

To Cut Glass.
Experiment 11
.--Lay the glass plate on a flat surface, and draw a steel glass-cutter--revolving wheel--over it, holding this against a ruler for a guide, and pressing down hard enough to scratch the glass. Then break it by holding between the thumb and fingers, having the thumbs on the side opposite to the scratch, and pressing them outward while bending the ends of the glass inward. The break will follow the scratch. Holes can be bored through glass and bottles with a broken end of a round file kept wet with a solution of camphor in oil of turpentine.

To Perforate Corks.
Experiment 12
.--First make a small hole in the cork with the pointed handle of a round--rat-tail--file. Have the hole perpendicular to the surface of the cork. This can be done by holding the cork in the left hand and pressing against the larger surface, or upper part, of the cork, with the file in the right hand. Only a mere opening is made in this way, which must be enlarged by the other end of the file. A second or third file of larger size may be employed, according to the size of the hole to be made, which must be a little smaller than the tube it is to receive, and perfectly round.

To Obtain Oxygen.
Experiment 13.
--Take 5 g. of crystals of potassium chlorate (KClO3) and, without pulverizing, mix with the same weight of pure powdered manganese dioxide (MnO2). Put the mixture into a test-tube, and insert a delivery-tube--having the cork fit tightly. Hang it on a ring-stand,-- as in Figure 7, having the other end of the delivery-tube under the shelf, in a pneumatic trough, filled with water just above the shelf. Fill three or more receivers--wide-mouthed bottles--with water, cover the mouth of each with a glass plate, invert it with its mouth under water, and put it on the shelf of the trough, removing the plate. No air should be in the bottles. Have the end of the delivery-tube so that the gas will rise through the orifice. Hold a lighted lamp in the hand, and bring the flame against the mixture in the test-tube Keep the lamp slightly in motion, with the hand, so as not to break the test-tube by over-heating in one place. Heat the mixture strongly, if necessary. The upper part of the test-tube is filled with air: allow this to escape for a few seconds; then move a receiver over the orifice, and fill it with gas. As soon as the lamp is taken away, remove the delivery-tube from the water. The gas contracts, on cooling, and if not removed, water will be drawn over, and the test-tube will be broken. Let the test-tube hang on the ring-stand till cool. With glass plates take out the receivers, leaving them covered, mouth upward (Fig. 8), with little or no water inside. When cool, the test-tube may be cleaned with water, by covering its mouth with the thumb or hand, and shaking it vigorously.

Experiment 14.--Examine the gas in one of the receivers. Put a lighted splinter into the receiver, sliding along the glass cover. Remove it, blow it out, and put in again while glowing. Is it re-kindled? Repeat till it will no longer burn. Is the gas a supporter of combustion? How did the combustion compare with that in air? Is it probable that air is pure O? Why did the flame at last go out? Has the O been destroyed, or chemically united with something else?

Combustion of Sulphur.
Experiment 15
.--Hollow out one end of a piece of electric-light pencil, or of crayon, 3 cm. long, and attach it to a Cu wire (Fig. 9). Put into this a piece of S as large as a pea, ignite it by holding in the flame, and then hold it in a receiver of O. Note the color and brightness of the flame, and compare with the same in the air. Also note the color and odor of the product. The new gas is SO2. Name it, and write the equation for its production from S and O. How do you almost daily perform a similar experiment? Is the product a supporter of combustion?

Combustion of Phosphorus.
Experiment 16
.--With forceps, which should always be used in handling this element, put a bit of P, half as large as the S above,into the crayon, called a deflagrating-spoon. Heat another wire, touch it to the P, and at once lower the latter into a receiver of O. Notice the combustion, the color of the flame and of the product. After removing, be sure to burn every bit of P by holding it in a flame, as it is liable to take fire if left. The product of the combustion is a union of what two elements? Is it an oxide? Its symbol is P2O5. Write the equation, using symbols, names, and weights. Towards the close of the experiment, when the O is nearly all combined, P2O3 is formed, as it is also when P oxidizes at a low temperature. Name it and write the equation.

Combustion of Iron.
Experiment 17
.--Take in the forceps a piece of iron picture-cord wire 6 or 8cm long, hold one end in the flame for an instant, then dip it into some S. Enough S will adhere to be set on fire by holding it in the flame again. Then at once dip it into a receiver of O with a little water in the bottom. The iron will burn with scintillations. Is this analysis or synthesis? What elements combine? A watch-spring, heated to take out the temper, may be used, but picture-wire is better.

Experiment 18.--Fasten a piece of electric-light pencil, or of crayon, to a wire, as in Experiment 15, and bend the wire so it will reach half-way to the bottom of a receiver. Using forceps, put into the crayon a small piece of phosphorus. Pass the wire up through the orifice in the shelf of a p.t. (pneumatic trough), having water at least l cm. above the shelf. Heat another wire, touch it to the P, and quickly invert an empty receiver over the P, having the mouth under water, so as to admit no air (Fig. 10). Let the P burn as long as it will, then remove the wire and the crayon, letting in no air. Note the color of the product, and leave till it is tolerably clear, then remove the receiver with a glass plate, leaving the water in the bottom.

Experiment 19.--When the white cloud has disappeared, slide the plate along, and insert a burning stick; try one that still glows. See whether the P and S on the end of a match will burn. Is the gas a supporter of combustion?

HYDROGEN Preparation.
Experiment 20
.--Prepare apparatus as for making O. Be sure that the cork perfectly fits both delivery-tube and test-tube, or the H will escape. Cover 5 g. granulated Zn, in the test-tube, with 10 cc. H2O, and add 5 cc. chlorhydric acid, HCl. Adjust as for O (Fig. 7), except that no heat is to be applied. If the action is not brisk enough, add more HCl. Collect several receivers of the gas over water, adding small quantities of HCl when necessary. Observe the black floating residuum; it is carbon, lead, etc. With a glass plate remove the receivers, keeping them inverted (Fig. 11), or the H will escape.

Experiment 21.--Lift with the left hand a receiver of H, still inverted, and insert a burning splinter with the right (Fig. 12). Does the splinter continue to burn? Does the gas burn? If so, where? Is the light brilliant? Note the color of the flame. Is there any explosion? Try this experiment with several receivers. Is the gas a supporter of combustion? i.e. will carbon burn in it? Is it combustible? i.e. does it burn? If so, it unites with some part of the air. With what part?34. Collecting H by Upward Displacement.

Experiment 22.--Pass a delivery-tube from a H generator to the top of a receiver or test-tube (Fig. 13). The escaping H being so much lighter than air will force the latter down. To obtain the gas unmixed with air, the delivery-tube should tightly fit a cardboard placed under the mouth of the receiver. When filled, the receiver can be removed, inverted as usual, and the gas tested. In this and other experiments for generating H, a thistle-tube, the end of which dips under the liquid, can be used for pouring in acid, as in Figure 13.

Philosopher's Lamp and Musical Flame.
Experiment 23
.--Fit to a cork a piece of glass tubing 10 or 15 cm. long, having the outer end drawn out to a point with a small opening, and insert it in the H generator. Before igniting the gas at the end of the tube take the, precaution to collect a test-tube of it by upward displacement, and bring this in contact with a flame. If a sharp explosion ensues, air is not wholly expelled from the generator, and it would be dangerous to light the gas. When no sound, or very little, follows, light the escaping gas. The generation of H must not be too rapid, neither should the test-tube be held under the face, as the cork is liable to be forced out by the pressure of H. A safety-tube, similar to the thistle- tube above, will prevent this. This apparatus is called the "philosopher's lamp." Thrust the flame into a long glass tube 1- 1/2 to 3 cm. in diameter, as shown in Figure 14, and listen for a musical note.

Product of Burning H in Air.
Experiment 24
.--Fill a tube 2 or 3 cm. in diameter with calcium chloride, CaCl2, and connect one end with a generator of H (Fig. 15). At the other end have a philosopher's lamp-tube.Observing the usual precautions, light the gas and hold over it a receiver, till quite a quantity of moisture collects. All water was taken from the gas by the dryer, CaCl2. What is, therefore, the product of burning H in air? Complete this equation and explain it: 2H + O = ? Figure 16 shows a drying apparatus arranged to hold CaCl2.

Explosiveness of H.
Experiment 25
. -- Fill a soda-water bottle of thick glass with water, invert it in a pneumatic trough, and collect not over 1/4 full of H. Now remove the bottle, still inverted, letting air in to fill the other 3/4. Mix the air and H by covering the mouth of the bottle with the hand, and shaking well; then hold the mouth of the bottle, slightly inclined, in a flame. Explain the explosion which follows. If 3/4 was air, what part was O? What use did the N serve? Note any danger in exploding H mixed with pure O. What proportions of O and H by volume would be most dangerously explosive? What proportion by weight? By the rapid union of the two elements, the high temperature suddenly expanded the gaseous product, which immediately contracted; both expansion and contraction produced the noise of explosion.

Experiment 26.--Hold a porcelain dish or a plate in the flame of a candle, or of a Bunsen burner with the openings at the bottom closed. After a minute examine the deposit. It is carbon, i.e. lamp- black or soot, which is a constituent of gas, or of the candle. Open the valve at the base of the Bunsen burner, and hold the deposit in the flame. Does the C gradually disappear? If so, it has been burned to CO2. C + 2 O = CO2. Is C a combustible element?

Experiment 27.--Ignite a splinter, and observe the combustion and the smoke, if any. Try to collect some C in the same way as before. With plenty of O and high enough temperature, all the C is burned to CO2, whether in gas, candle, or wood. CO2 is an invisible gas. The porcelain, when held in the flame, cools the C below the point at which it burns, called the kindling-point, and hence it is deposited. The greater part of smoke is unburned carbon.

Experiment 28.--Hold an inverted dry test-tube or receiver over the flame of a burning candle, and look for any moisture (H2O). What two elements are shown by these experiments to exist in the candle? The same two are found in wood and in gas.

Experiment 29.--Put into a small Hessian crucible (Fig. 18) some pieces of wood 2 or 3 cm long, cover with sand, and heat the crucible strongly. When smoking stops, cool the crucible, remove the contents, and examine the charcoal. The gases have been driven off from the wood, and the greater part of what is left is C.

Experiment 30.--Put 1 g. of sugar into a porcelain crucible, and heat till the sugar is black. C is left. See Experiment 5. Remove the C with a strong solution of sodium hydrate

C a Reducing Agent.
Experiment 31.
--Put into a small ignition-tube a mixture of 4 or 5 g. of powdered copper oxide (CuO), with half its bulk of powdered charcoal. Heat strongly for ten or fifteen minutes. Examine the contents for metallic copper. With which element of CuO has C united?

C a Decolorizer.
Experiment 32
.--Put 3 or 4 g. of bone-black into a receiver, and add 10 or 15 cc.of cochineal solution. Shake this thoroughly, covering the bottle with the hand. Then pour the whole on a filter paper, and examine the filtrate. If all the color is not removed, filter again. What property of C is shown by this experiment? Any other coloring solution may be tried.

C a Disinfectant.
Experiment 33
.--Repeat the previous experiment, adding a solution of H2S3 i.e. hydrogen sulphide, in water, instead of cochineal solution. See page 120. Note whether the bad odor is removed. If not, repeat.

C an Absorber of Gases and a Retainer of Heat.
Experiment 34
.--Put a piece of phosphorus of the size of a pea, and well dried, on a thick paper. Cover it well with bone-black, and look for combustion after a while. O has been condensed from the air, absorbed by the C, and thus communicated to the P. Burn all the P at last.

Deposition of Silver.
Experiment 35
.--Put a ten-cent Ag coin into an evaporating-dish, and pour over it a mixture of 5 cc. HNO3 and 10 cc. H2O. Warm till all, or nearly all, the Ag dissolves. Remove the lamp. 3 Ag + 4 HNO3 = 3 AgNO3 + 2 H2O + NO. Then add 10 cc. H2O, and at once put in a short piece of Cu wire, or a cent. Leave till quite a deposit appears, then pour off the liquid, wash the deposit thoroughly, and remove it from the coin. See whether the metal resembles Ag.

Deposition of Copper. Experiment 36.--Dissolve a cent or some Cu turnings in dilute HNO3, as in Experiment 35, and dilute the solution. 3 Cu + 8 HN09 - 3 Cu (NOA+4 H2O+2 NO.) Then put in a clean strip of Pb, and set aside as before, examining the deposit finally.

Deposition of Lead.
Experiment 37
.--Perform this experiment in the same manner as the two previous ones, dissolving a small piece of Pb, and using a strip of Zn to precipitate the Pb. 3 Pb + 8 HNO3 - 3 Pb (NO4)2 + 4 Ha0 + 2 NO. Pb (NO3) 2 + Zn = ? h.

Decomposition of Water.
Experiment 38
.--Arrange "in series" two or more cells of a Bunsen battery (Physics, page 164), [References are made in this book to Gage's Introduction to Physical Science.] and attach the terminal wires to an electrolytic apparatus (Fig. 19) filled with water made slightly acid with H2SO4. Construct a diagram of the apparatus, marking the Zn in the liquid +, since it is positive, and the C, or other element, -. Mark the electrode attached to the Zn -, and that attached to the C +; positive electricity at one end of a body commonly implies negative at the other. Opposites attract, while like electricities repel each other. These analogies will aid the memory. At the + electrode is the - element of H2O, and at the - electrode the + element. Note, page 43, whether H or O is positive with reference to the other, and write the symbol for each at the proper electrode. Compare the diagram with the apparatus, to verify your conclusion. Why does gas collect twice as fast at one electrode as at the other? What does this prove of the composition of water? When filled, test the gases in each tube, for O and H, with a burning stick.

Experiment 39.--Pour a few drops of chlorhydric acid, HCl, into a clean evaporating-dish. Add 5 cc. H2O, and stir. Touch a drop to the tongue, noting the taste. Dip into it the end of a piece of blue litmus paper, and record the result. Thoroughly wash the dish, then pour in a few drops of nitric acid, HNO3, and 5 cc. H2O, and stir. Taste, and test with blue litmus. Test in the same way sulphuric acid, H2SO4.

Experiment 40.--Hold a piece of wet blue litmus paper in the fumes of SO2, and note the acid test. Try the same with dry litmus paper.

Experiment 41.--Burn a little S in a receiver of air containing 10 cc. H2O, and loosely covered, as in the O experiment. Then shake to dissolve the SO2. H2O + SO2 = H2SO3. Apply test paper.

Experiment 42.--Put a few drops of NH4OH into an evaporating- dish. Add 5 cc. H2O, and stir. Taste a drop. Dip into it a piece of red litmus paper, noting the effect. Cleanse the dish, and treat in the same way a few drops NaOH solution, recording the result. Do the same with KOH. Acid stains on the clothing, with the exception of those made by HNO3, maybe removed by NH4OH. H2SO4, however, rapidly destroys the fiber of the cloth.

Experiment 43.--Pour 5 cc. of a solution of litmus in water, into a clean test-tube or small beaker. Pour 2 or 3 cc. of HCl into an evaporating-dish, and the same quantity of NH4OH into another dish. Take a drop of the HCl on a stirring-rod and stir the litmus solution with it. Note the acid reaction. Clean the rod, and with it take a drop (or more if necessary) of NH4OH, and add this to the red litmus solution, noting the alkaline reaction. Experiment in the same way with the two other principal acids and the two other alkalies.

Experiment 44.--Put into an evaporating-dish 5 cc. of NaOH solution. Add HCl to this from a test-tube, a few drops at a time, stirring the mixture with a glass rod (Fig. 20), and testing it with litmus paper, until the liquid is neutral, i.e. will not turn the test paper from blue to red, or red to blue. Test with both colors. If it turns blue to red, too much acid has been added; if red to blue, too much base. When it is very nearly neutral, add the reagent, HCl or NaOH, a drop at a time with the stirring-rod. It must be absolutely neutral to both colors. Evaporate the water by heating the dish over asbestus paper, wire gauze, or sand, in an iron plate (Fig. 21) till the residue becomes dry and white. Cool the residue, taste, and name it. The equation is: HCl + NaOH = NaCl + HOH or H2O. Note which elements, positive or negative, change places. Why was the liquid boiled? The residue is a type of a large class of compounds, called salts.

Experiment 45. -- Experiment in the same way with KOH solution and H2SO4, applying the same tests. H2SO4 + 2 KOH = K2SO4 + 2 HOH. What is the solid product?

Experiment 46.--Neutralize NH4OH with HNO3, evaporate, apply the tests, and write the equation. Write equations for the combination of NaOH and H2SO4; NaOH and HNO3; KOH and HCl; KOH and HNO3; NH4OH and HCl; NH4OH and H2SO4. Describe the experiment represented by each equation, and be sure you can perform it if asked to do so. What is the usual action of a salt on litmus? How is a salt made? What else is formed at the same time? Have all salts a saline taste? Does every salt contain a positive element or radical? A negative?

Preparation of HCl.
Experiment 47.
--Into a flask put 10 g. coarse NaCl, and add 20 cc. H2SO4. Connect with Woulff bottles [Woulff bottles may be made by fitting to wide-mouthed bottles corks with three holes, through which pass two delivery tubes, and a central safety tube dipping into the liquid, as in Figures 22 and 23.] partly filled with water, as in Figure 22. One bottle is enough to collect the HCl; but in that case it is less pure, since some H2SO4 and other impurities are carried over. Several may be connected, as in Figure 23. The water in the first bottle must be nearly saturated before much gas will pass into the second. Heat the mixture 15 or 20 minutes, not very strongly, to prevent too much foaming. Notice any current in the first bottle. NaCl + H2SO4 = HNaSO4 + HCl. Intense heat would have given: 2NaCl + H2SO4 = Na2SO4 + 2HCl. Compare these equations with those for HNO3. In which equation above is H2SO4 used most economically? Both reactions take place when HCl is made on the large scale.

Experiment 48.--(1) Test with litmus the liquid in each Woulffbottle. (2) Put a piece of Zn into a test-tube and cover it with liquid from the first bottle. Write the reaction, and test the gas. (3) To 2 cc.solution AgNO3 in a test-tube add 2 cc.of the acid. Describe, and write the reaction. Is AgCl soluble in water? (4) Into a test-tube pour 5 cc.Pb(NO3)2 solution, and add the same amount of prepared acid. Give the description and the reaction. (5) In the same way test the acid with Hg2(NO3)2 solution, giving the reaction. (6) Drake a little HCl in a test-tube, and bring the gas escaping from the delivery-tube in contact with a burning stick. Does it support the combustion of C? (7) Hold a piece of dry litmus paper against it. [figure 23] (8) Hold it over 2 cc.of NH4OH in an evaporating-dish.

Experiment 49.--Put into a test-tube 2 cc. AgNO3 solution, add 5 cc. H2O, then add slowly HCl so long as a ppt. (precipitate) is formed. This ppt. is AgCl. Now in another test-tube put 2 cc. Cu(NO3)2, solution, add 5 cc. H2O, then a little HCl. No ppt. is formed. Now if a solution of AgNO3 and a solution of Cu(NO3)2 were mixed, and HCl added, it is evident that the silver would be precipitated as chloride of silver, while the copper would remain in solution. If now this be filtered, the silver will remain on the filter paper, while in the filtrate will be the copper. Thus we shall have performed an analysis, or separated one metal from another. Perform it. Note, however, that any soluble chloride, as NaCl, would produce the same result as HCl.

To make HI.
Experiment 50
.--Drop into a test-tube three or four crystals of I, and add 10 cc. H2O. Hold in the water the end of a delivery-tube from which H2S gas is escaping. Observe any deposit, and write the reaction.

Preparation and Action.
Experiment 51
.--Put 3 or 4 g. powdered CaF2, i.e. fluor spar or fluorite, into a shallow lead tray, e.g. 4x5 cm, and pour over it 4 or 5 cc. H2SO4. A piece of glass large enough to cover this should previously be warmed and covered on one side with a very thin coat of beeswax. To distribute itevenly, warm the other side of the glass over a flame. When cool, scratch a design (Fig. 24) through the wax with a sharp metallic point. Lay the glass, film side down, over the lead tray. Warm this five minutes or more by placing it high over a small flame (Fig. 25) to avoid melting the wax. Do not inhale the fumes. Take away the lamp, and leave the tray and glass where it is not cold, for half an hour or more. Then remove the wax and clean the glass with naphtha or benzine. Look for the etching.

Experiment 52
.--To 10 g. KNO3 or NaNO3, in a flask, add 15 cc. H2SO4. Securely fasten the cork of the delivery-tube, as HNO3 is likely to loosen it, and pass the other end to the bottom of a test-tube held deep in a bottle of water (Fig. 26). Apply heat, and collect 4 or 5 cc.of the liquid. The usual reaction is: KNO3 + H2SO4 = HKSO4 + HNO3. With greater heat, 2 KNO3 + H2SO4 = K2SO4 + 2HNO3. Which is most economical of KNO3? Of H2SO4? Instead of a flask, a test-tube may be used if desired (Fig. 27).

Experiment 53.--(1) Note the color of the prepared liquid. (2) Put a drop on the finger; then wash it off at once. (3) Dip a quill or piece of white silk into it; then wash off the acid. What color is imparted to animal substances? (4) Add a little to a few bits of Cu turnings, or to a Cu coin. Write the equation. (5) To 2 cc.indigo solution, add 2 cc. HNO3. State the leading properties of HNO3, from these tests.

Preparation and Action.
Experiment 54
.--Into a test-tube put 2 cc. HNO3, and 14 qcm. of either Au leaf or Pt. Warm in a flame. If the metal is pure, no action takes place. Into another tube put 6 cc. HCl and add a similar leaf. Heat this also. There should be no action. Pour the contents of one test-tube into the other. Note the effect. Which is stronger, one of the acids, or the combination of the two? Note the odor. It is that of Cl. 3HCl + HNO3 = NOCl + 2H2O + Cl2. This reaction is approximate only. The strength is owing to nascent chlorine, which unites with Au. Au + 3Cl = AuCl3. If Pt be used, PtCl4 is produced. No other acid except nitro-hydrochloric will dissolve Au or Pt; hence the ancients called it aqua regia, or king of liquids. It must be made as wanted, since it cannot be kept and retain its strength.

Experiment 55
.--Having fitted a cork with four or five perforations to a large test-tube, pass a delivery-tube from three of these to three smaller test-tube, leaving the others open to the air, as in Figure 28. Into one test-tube put 5 cc. H2O, into another 5 g. Cu turnings and 10 cc. H2SO4, into the third 5 g. Cu turnings and 10 cc. dilute HNO3, half water. Hang on a ring stand, and slowly heat the tubes containing H2O and H2SO4. Notice the fumes that pass into the large test-tube

Tests for H2SO4.
Experiment 56
.--(1) Test the liquid with litmus. (2) Transfer it to a test-tube, and add an equal volume of BaCl2 solution. H2SO4 + BaCl2 = ? Is BaSO4 soluble? (3) Put one drop H2SO4 from the reagent bottle in 10 cc. H2O in a clean test-tube, and add 1 cc. BaCl2 solution. Look for any cloudiness. This is the characteristic test for H2SO4 and soluble sulphates, and so delicate that one drop in a liter of H2O can be detected. (4) Instead of H2SO4, try a little Na2SO4 solution. (5) Put two or three drops of strong H2SO4 on writing-paper, and evaporate, high over a flame, so as not to burn the paper. Examine it when dry. (6) Put a stick into a test-tube containing 2 cc. H2SO4, and note the effect. (7) Review Experiment 5. (8) Into an evapourating-dish pour 5 cc. H2O, and then 15 cc. H2SO4. Stir it meantime with a small test-tube containing 2 or 3 cc. NH4OH, and notice what takes place in the latter; also note the heat of the evapourating-dish

Preparation of NH4OH and NH3.
Experiment 57
.--Powder 10 g. ammonium chloride, NH4Cl, in a mortar and mix with 10 g. calcium hydrate, Ca(OH)2; recently slaked lime is the best. Cover with water in a flask, and connect with Woulff bottles, as for making HCl (Fig. 22); heat the flask for fifteen minutes or more. The experiment may be tried on a smaller scale with a test-tube if desired.

Experiment 58.--Powder and mix 2 or 3 g. each of ammonium nitrate, NH4NO3, and Ca(OH)2; put them into a test-tube, and heat slowly. Note the odor. 2NH4NO3 + Ca(OH)2 = ?

Experiment 59.--(1) Generate a little of the gas in a test-tube, and note the odor. (2) Test the gas with wet red litmus paper. (3) Put a little HCl into an evapourating-dish, and pass over it the fumes of NH3 from a delivery-tube Note the result, and write the equation. (4) Fill a small test-tube with the gas by upward displacement; then, while still inverted, put the mouth of the test-tube into water. Explain the rise of the water. (5) How might NH4Cl be obtained from the NH4OH in the Woulff bottles? (6) Test the liquid in each bottle with red litmus paper. (7) Add some from the first bottle to 5 or 10 cc. of a solution of FeSO4 or FeCl2, and look for a ppt.

Experiment 60.--Into a test-tube put 10 cc. of a solution of ferrous sulphate, FeSO4. Into another put 10 cc. of sodium sulphate solution, Na2SO4. Add a little NH4OH to each. Notice a ppt. in the one case but none in the other. If solutions of these two compounds were mixed, the metals Fe and Na could be separated by the addition of NH4OH, similar to the separation of Ag and Cu by HCl. Try the experiment.

Experiment 61.--Dissolve 3 g. sodium carbonate, Na2CO3, in 10 or 15 cc. H2O in an evapourating-dish, and bring it to the boiling-point. Then add to this a mixture of 1 or 2 g. calcium hydrate, Ca(OH)2, in 5 or 10cc. H2O. It will not dissolve. Boil the whole for five minutes. Then pour off the liquid which holds NaOH in solution. Evaporate if desired. This is the usual mode of preparing NaOH.

Experiment 62.--Put 20 cc. of H2O in a receiver. With the forceps take a piece of Na, not larger than half a pea, from the naphtha in which it is kept, drop it into the H2O, and at once cover the receiver loosely with paper or cardboard. Watch the action, as the Na decomposes H2O. HOH + Na = NaOH + H. If the water be hot the action is so rapid that enough heat is produced to set the H on fire. That the gas is H can be shown by putting the Na under the mouth of a small inverted test-tube, filled with cold water, in a water-pan. Na rises to the top, and the test-tube fills with H, which can be tested. NaOH dissolves in the water.102. Properties.

Experiment 63.--(1) Test with red litmus paper the solutions obtained in the last two experiments. (2) To 5cc.of alum solution, K2A12(SO4)4, add 2cc.of the liquid, and notice the color and form of the ppt.

Experiment 64.--Drop a small piece of K into a receiver of H2O, as in Experiment 62. The K must be very small, and the experiment should not be watched at too close a range. The receiver should not be covered with glass, but with paper. The H burns, uniting with O of the air. The purple color is imparted by the burning, or oxidation of small particles of K. Write the equation for the combustion of each.

Experiment 65.--Saturate some unslaked lime with water, in an evapourating-dish, and look for the results stated above, leaving it as long as may be necessary.

Experiment 66
.--Put into a flask, holding 200cc, lOg of ammonium nitrate, NH4NO3; heat it over wire gauze or asbestus in an iron plate, having a delivery-tube connected with a large test-tube, which is held in a receiver of water, and from this test-tube, another delivery-tube passing into a pneumatic trough, so as to collect the gas over water (Fig. 30). Have all the bearings tight. The reaction is NH4NO3 = 2H2O + N2O. The test-tube is for collecting the H2O. Note the color of the liquid in the test-tube; taste a drop, and test it with litmus. If the flask is heated too fast, some NO is formed, and this taking O from the air makes NO2, which liquefies and gives an acid reaction and a red color. Some NH4NO3 is also liable to be carried over.

Experiment 67.--Test the gas in the receiver with a burning stick and a glowing one, and compare the combustion with that in O. N20may also be tested with S and P, if desired. N is set free in each case. Write the reactions. Nitrogen monoxide or protoxide, the nitrous oxide of dentists, when inhaled, produces insensibility to pain,-- anaesthesia,-- and, if continued, death from suffocation. Birds die in half a minute from breathing it. Mixed with one-fourth O, and inhaled for a minute or two, it produces intoxication and laughter, and hence is called laughing gas. As made in Experiment 66, it contains Cl and NO, as impurities, and should not be breathed.

Experiment 68
.--Into a test-tube or receiver put 5g Cu turnings, add 5 cc. H2O and 5 cc. HNO3. Collect the gas like H, over water. 3Cu + 8HNO3 = ? What two products will be left in the generator? Notice the color of the liquid. This color is characteristic of Cu salts. Notice also the red fumes of NO2.

Experiment 69
.--Test the gas with a burning stick, admitting as little air as possible. Test it with burning S. NO is not a supporter of C and S combustion. Put a small bit of P in a deflagrating-spoon, and when it is vigorously burning, lower it into the gas. It should continue to burn. State the reaction. What combustion will NO support? Note that NO is half N, while N2O is two-thirds N, and account for the difference in supporting combustion.

Experiment 70
.--Lift from the water-pan a receiver of NO, and note the colored fumes. They are NO2, or N2O4, nitrogen tetroxide. NO + O = NO2. Is NO combustible? What is the source of O in the experiment?OXIDES OF NITROGEN.

Experiment 71
.--Put into a test-tube 1 g. of starch and 1 cc. of HNO3. Heat the mixture for a minute. The red fumes are N2O3 and NO2. Nitrogen pentoxide, N2O5, is an unimportant solid. United with water it forms HNO3. N2O5 + H2O = 2HNO3.

Experiment 72
.--Put into a flask, of 200 cc., 5 g. of oxalic acid crystals, H2C2O4, and 25 cc. H2SO4. Have the delivery-tube pass into a solution of NaOH in a Woulff bottle (Fig. 31), and collect the gas over water. Heat the flask slowly, and avoid inhaling the gas.

Experiment 73.--Remove a receiver of the gas, and try to light the latter with a splinter. Is it combustible, or a supporter of (C) combustion? What is the color of the flame? When the combustion ceases, shake up a little lime water with the gas left in the receiver. What gas has been formed by the combustion, as shown by the test?

Experiment 74.--Put into a test-tube, or a bottle with a delivery-tube and a thistle-tube, 10 or 20 g. CaCO3, marble in lumps; add as many cubic centimeters of H2O, and half as much HCl, and collect the gas by downward displacement (Fig. 39). Add more acid as needed. CaCO3 + 2 HCl = CaCl2 + H2CO3. H2CO3 = H2O + CO2. H2CO3 is a very weak compound, and at once breaks up. By some, its existence as a compound is doubted.

Experiment 75.--(1) Put a burning and a glowing stick into the test-tube or bottle. (2) Hold the end of the delivery-tube directly against the flame of a small burning stick. Does the gas support combustion? (3) Pour a receiver of the gas over a candle flame. What does this show of the weight of the gas? (4) Pass a little CO2 into some H2O (Fig. 32), and test it with litmus. Give the reaction for the solution of CO2 in H2O.

Experiment 76.--Put into a test-tube 51 cc. of clear Ca(OH)2 solution, i.e. lime water; insert in this the end of a delivery-tube from a CO2 generator (Fig. 32). Notice any ppt. formed. It is CaCO3. Let the action continue until the ppt. disappears and the liquid is clear. Then remove the delivery-tube, boil the clear liquid for a minute, and notice whether the ppt. reappears.

Experiment 77.--(1) Put a little lime water into a test-tube, and blow into it through a piece of glass tubing. Any turbidity shows what? (2) Burn a candle for a few minutes in a receiver of air, then take out the candle and shake up lime water with the gas. (3) Expose some lime water in an evapourating-dish to the air for some time.

Experiment 78
.--Scrape off the oxide from the surface of a piece of phosphorus 2 cm long, put it into a wide-mouthed bottle, half cover the P with water, cover the bottle with a glass, and leave it for half an hour or more.

Experiment 79.--Remove the glass cover, smell the gas, and hold in it some wet iodo-starch paper. Look for any blue color. Iodine has been set free, according to the reaction, 2 KI + 03= K20 + O2 + I2, and has imparted a blue color to the starch, and ordinary oxygen has been formed.

Experiment 80.--Provide a glass tube 40 or 50 cm long and 3 or 4 cm in diameter. Fit to each end a cork with two perforations, through one of which a long tube passes the entire length of the larger tube (Fig. 32a). Connect one end of this with a flask of water arranged for heating; pass the other end into an open receptacle for collecting the distilled water. Into the other perforations lead short tubes,-- the one for water to flow into the large tube from a jet; the other, for the same to flow out. This condenses the steam by circulating cold water around it. The apparatus is called a Liebig's condenser. Put water into the flask, boil it, and notice the condensed liquid. It is comparatively pure water; for most of the substances in solution have a higher boiling-point than water, and are left behind when it is vaporized.

Experiment 81.--Test the purity of distilled water by slowly evaporating a few drops on Pt foil in a room free from dust. There should be no spot or residue left on the foil.

Experiment 82.--Examine a candle flame, holding a dark object behind it. Note three distinct portions: (1) a colorless interior about the wick, (2) a yellow light-giving portion beyond that, (3) a thin blue envelope outside of all, and scarcely discernible. Hold a small stick across the flame so that it may lie in all three parts, and observe that no combustion takes place in the inner portion.

Experiment 83.--Examine a Bunsen burner. Unscrew the top, and note the orifices for the admission of gas and of air. Make a drawing. Replace the parts; then light the gas at the top, opening the air-holes at the base. Notice that the flame burns with very little color. Try to distinguish the three parts, as in the candle flame. These parts can best be seen by allowing direct sunlight to fall on the flame and observing its shadow on a white ground. Make a drawing of the flame. Hold across it a Pt wire and note at what part the wire glows most. Also press down on the flame for an instant with a cardboard or piece of paper; remove before it takes fire, and notice the charred circle. Put the end of a match into the blue cone, and note that it does not burn. Put the end of a Pt wire into this blue cone, and observe that it glows when near the top of the cone. What do these experiments show? Ascertain whether this inner portion contains a combustible material, by holding in it one end of a small delivery-tube, and trying to ignite any gas escaping at the other end. It should burn. This shows that no combustion takes place in the interior of the flame, because sufficient free O is not present. Next, close the air-holes, and note that the flame is yellow and gives much light. From this we infer the presence of solid particles in an incandescent state. But these could not come from the air. They must be C particles which have been set free from the C and H compounds of the gas, just as in the candle flame. The smoke that rises proves this. Hold an evapourating-dish in the flame and collect some C. Try the same with the air-holes open. 144. Light and Heat of Flame.--Which of the two flames is hotter, the one with the air-holes open, or that with them closed? Evidently the former; for air is drawn in and mixes with the gas as it rises in the tube, and, on reaching the flame at the top, the two are well mingled, and the gaseous compounds of C and H burn at so high a temperature that solid C is not freed; hence there is little light. On closing the air-holes, no O can reach the flame except from the outside, and the heat is much less intense.

Experiment 84.--Light a Bunsen flame, with the basal orifices open, and hold over it a fine wire gauze. Notice that the flame does not rise above the gauze. Extinguish the light, and try to ignite the gas above the gauze, holding the latter within 5 or 6 cm of the burner tube. Notice that it does not burn below the gauze

Experiment 85.--Fit a cork with two holes in it to the large end of a lamp chimney. Through each hole pass a short piece of tubing, and connect one of these with a rubber tube leading to a gas-jet. Pass a metallic tube, long enough to reach the top of the chimney, through the other, so that it will move easily up and down. Turn on the gas, and light it at the top of the chimney. Hold the end of the tube passing through the cork in the flame for a minute, then draw it down to the middle of the chimney (Fig. 37, a) and finally slowly remove it (b). Note that O from the air is burning in the gas. Which is the supporter, and which the combustible in this case? O will burn equally well in an atmosphere of H, as can be shown by experiment.

Explosive Mixture of Gases.
Experiment 86
.--Slowly turn down the burning gas of a Bunsen lamp, having the orifices open, and notice that it suddenly explodes and goes out at the top, but now burns at the base. As the gas was gradually turned off, more air became mixed with it, until there was the right proportion of each gas for an explosion. Figure 38 shows the same thing. Light the gas at the top a, when the tube c covers the jet b. Then gradually raise the tube c. At a certain place there is the same explosion as with the lamp.

Experiment 87
.--Put into a test-tube 5 g. of fine granular MnO2 and 10 cc. HCl. Apply heat carefully, and collect the gas by downward displacement in a receiver loosely covered with paper (Fig. 39). Add more HCl if needed. Have a good draft of air, and do not inhale the gas. If you have accidentally breathed it, inhale alcohol vapor from a handkerchief; alcohol has great affinity for Cl. Note the color of the gas, and compare its weight with that of air. If preferred, a flask may be used for a generator instead of a test-tube Cl can be obtained directly from NaCl by adding H2SO4 (which produces HCl) and MnO2. 2 NaCl + 2 H2SO4 + MnO2 = MnSO4 + Na2SO4 + 2 H2O + 2 Cl. Try the experiment, using a test-tube and adding water.

Cl from Bleaching-Powder.
Experiment 88
.--Put a few grams of bleaching- powder into a small beaker, and set this into a larger one. Cover the latter with pasteboard or paper, through which passes a thistle-tube reaching into the small beaker (Fig. 40). Pour through the tube a little H2SO4 dilated with its volume of H2O.

Chlorine Water.--A solution of Cl in water is often useful, and may be made as follows:--
Experiment 89
.--To 3 or 4 crystals of KClO3 add a few drops of HCl. Heat a minute, and when the gas begins to disengage, pour in 10 cc. H2O, which dissolves the gas. 2 KClO3 + 4 HCl = 2 KCl + Cl2O4 + 2 H2O + 2 Cl.

Bleaching Properties.
Experiment 90
.--Put into a receiver of Cl, preferably before generating it, two pieces of Turkey red cloth, one wet, the other dry; a small piece of printed paper and a written one; also a red rose or a green leaf, each wet. Note from which the color is discharged. If it is not discharged from all, put a little H2O into the receiver, shake it well, and state what ones are bleached.

Experiment 91.--(1) Add 5 cc. of Cl water to 5 cc. of indigo solution. (2) Treat in the same way 5 cc. K2Cr2O7 (potassium dichromate) solution, and record the results. Indigo, writing-ink, and Turkey red or madder, are vegetable pigments; printer's ink contains C, and K2Cr2O7 is a mineral pigment. State what coloring matters Cl will bleach.

Disinfecting Power.
Experiment 92
.--Pass a little H2S gas from a generator into a test-tube containing Cl water. Look for a deposit of S. Notice that the odor of H2S disappears. H2S + 2 Cl = 2 HCl + S.

A Supporter of Combustion.
Experiment 93
.--Sprinkle into a receiver of Cl a very little fine powder or filings of Cu, As, or Sb, and notice the combustion. Observe that here is a case of combustion in which O does not take part. Chlorides of the metals are of course formed. Write the reactions. See whether Cl will support the combustion of paper or of a stick of wood.

Experiment 94.--Warm 2 or 3 cc. of oil of turpentine (C1OH16) in an evaporating-dish; dip a piece of tissue paper into it, and very quickly thrust this into a receiver of Cl. It should take fire and deposit carbon. C1OH16 + 16 Cl = ? Test the moisture on the sides of the receiver with litmus. Clean the receiver with a little petroleum.

Experiment 95.--Prepare a H generator with a lamp-tube bent as in Figure 41. Light the H, observing the cautions in Experiment 23, and when well burning, lower the flame into a receiver of Cl. Observe the change of color which the flame undergoes as it comes in contact with Cl. Give the reaction for the burning. Test with litmus any moisture on the sides of the receiver. A mixture of Cl and H, in direct sunlight combines with explosive violence; whereas in diffused sunlight it combines slowly, and in darkness it does not combine. From these experiments state the chief properties of Cl, and what combustion it will support.

Experiment 96.--Pulverize 2 or 3 g. KBr, and mix it with about the same bulk of MnO2. After putting this into a t.t, add as much H2SO4, mix them together by shaking, attach a delivery-tube, and conduct the end of it into a test-tube that is immersed in a bottle of cold water. Slowly heat the contents of the test-tube, and notice the color of the escaping vapor, and any liquid that condenses in the receiver. Avoid inhaling the fumes, or getting them into the eyes.

Experiment 97.--Try the bleaching action of Br vapor as in the case of Cl. Bleach a piece of litmus paper, and try to restore the color with NH4OH. Explain its bleaching and disinfecting action. Try the combustibility of As, Sb, and Cu.

Preparation of I.
Experiment 98
.--Put into a test-tube 2 or 3 g. of powdered KI mixed with an equal bulk of MnO2, add H2SO4 enough to cover well, shake together, complete the apparatus as for making Br, and heat. Notice the color of the vapor, and any sublimate. The direct product of the solidification of a vapor is called a sublimate. The process is sublimation. Observe any crystals formed. Write the reaction, and compare the process with that for making Br and Cl. Compare the vapor density of I with that of Br and of Cl. With that of air. What vapor is heavier than I? What acid and what base are represented by KI?

Experiment 99.--(1) Put a crystal of I in the palm of the hand and watch it for a minute. (2) Put 2 or 3 crystals into a test-tube, and warm it, meanwhile holding a stirring-rod half-way down the tube. Notice the vapor, also a sublimate on the sides of the test-tube and rod. (3) Add to 2 or 3 crystals in a test-tube 5 cc. of alcohol, C2H5OH; warm it, and see whether a solution is formed. If so, add 5 cc. H2O and look for a ppt. of I. Does this show that I is not at all soluble in H2O, or not so soluble as in alcohol?

Starch Solution and Iodine Test.
Experiment 100
.--Pulverize a gram or two of starch, put it into an evaporating-dish, add 4 or 5 drops of water, and mix; then heat to the boiling-point 10 cc. H2O in a test-tube, and pour it over the starch, stirring it meanwhile. (1) Dip into this starch paste a piece of paper, hold it in the vapor of I, and look for a change of color. (2) Pour a drop of the starch paste into a clean test-tube, and add a drop or two of the solution of I in alcohol. Add 5 cc. H2O, note the color, then boil, and finally cool. (3) The presence of starch in a potato or apple can be shown by putting a drop of I solution in alcohol on a slice of either, and observing the color. (4) Try to dissolve a few crystals of I in 5 cc. H2O by boiling. If it does not disappear, see whether any has dissolved, by touching a drop of the water to starch paste. This should show that I is slightly soluble in water.

Iodo-Starch Paper.
Experiment 101
.--Add to some starch paste that contains no I 5 cc. of a solution of KI, and stir the mixture. Why is it not colored blue? Dip into this several strips of paper, dry them, and save for use. This paper is called iodo-starch paper, and is used as a test for ozone, chlorine, etc. Bring a piece of it in contact with the vapor of chlorine, bromine, or ozone, and notice the blue color.

Experiment 102.--Add a few drops of chlorine water to 2cc. of the starch and KI solution in 10 cc. H2O. This should show the same effect as the previous experiment.

Experiment 103.--To a solution of 2 g. of sodium sulphide,, Na2S2 in 10 cc. H2O add 3 or 4cc. HCl, and look for a ppt. Filter, and examine the residue. It is lac sulphur, or milk of sulphur.

Crystals from Fusion.
Experiment 104
.--In a beaker of 25 or 50 cc. capacity put 20 g. brimstone. Place this over a flame with asbestos paper interposed, and melt it slowly. Note the color of the liquid, then let it cool, watching for crystals. When partly solidified pour the liquid portion into an evapo- rating-dish of water, and observe the crystals of S forming in the beaker (Fig. 42). The hard mass may be separated from the glass by a little HNO3 and a thin knife-blade, or by CS2.

Experiment 105
.--Place in a test-tube 15g of brimstone, then heat slowly till it melts. Notice the thin amber-colored liquid. The temperature is now a little above 100 degrees. As the heat increases, notice that it grows darker till it becomes black and so viscid that it cannot be poured out. It is now above 200 degrees. Still heat, and observe that it changes to a slightly lighter color, and is again a thin liquid. At this time it is above 300 degrees. Now pour a little into an evaporating dish containing water. Examine this, noticing that it can be stretched like rubber. Leave it in the water till it becomes hard. Continue heating thebrimstone in the test-tube till it boils at about 450 degrees, and note the color of the escaping vapor. Just above this point it takes fire. Cool the test-tube, holding it in the light meantime, and look for a sublimate of S on the sides.

Experiment 106
.--Place in an evaporating-dish a gram of powdered brimstone, and add 5cc, CS2, carbon disulphide. Stir, and see whether S is dissolved. Put this in a draft of air, and note the evaporation of the liquid CS2, and the deposit of S crystals. These crystals are different in form from those resulting from cooling from fusion.

Experiment 107.-Test its bleaching power by burning S under a receiver under which a wet rose or a green leaf is also placed.

Experiment 108.--Put a gram of ferrous sulphide (FeS) into a test-tube fitted with a delivery-tube, as in Figure 32. Add 10cc. H2O and 5cc. H2SO4. H2S is formed. Write the equation, omitting H2O. What is left in solution?

Experiment 109.-(1) Take the odor of the escaping gas. (2) Pour into a test-tube 5cc.solution AgNO3, and place the end of the delivery-tube from a H2S generator into the solution and note the color of the ppt. What is the ppt.? Write the equation. (3) Experiment in the same way with Pb(NO3)2 solution. Write the equation. (4) Let some H2S bubble into a test-tube of clean water. To see whether H2S is soluble in H2O, put a few drops of the water on a silver coin. Ag2S is formed. Describe, and write the equation. Do the same with a copper coin. (5) Put a drop of lead acetate solution, Pb(C2H3O2)2, on a piece of unglazed paper, and hold this before the delivery-tube from which H2S is escap- ing. PbS is formed. Write the equation. This is the characteristic test of H2S.

Combustion of H2S
Experiment 110
.--Attach a philosopher's lamp tube to the H2S generator, and, observing the same precautions as with H, light the gas. What two products must be formed? State the reaction. The color of the flame. Compute the molecular weight and the vapor density of H2S. 194. Uses. -Hydrogen sulphide or sulphuretted hydrogen, H2S, is employed chiefly as a reagent in the chemical laboratory. It forms sulphides with many of the metals, as shown in the last experiment. These are precipitated from solution, and may be separated from other metals which are not so precipitated, as was found in the case of HCl and NH4OH. The subjoined experiment will illustrate this. Suppose we wished to separate Pb from Ba, having salts of the two mixed together, as Pb(NO3)2 and Ba(NO3)2.

H2S an Analyzer of Metals.
Experiment 111
.--Pass Some H2S gas in to 5cc.solution Ba(NO3)2. No ppt. is formed. Do the same with Pb(NO3)2 solution. A ppt. appears. Now mix 5cc.of each of these solutions in a test-tube and pass the gas from a H2S generator into the liquid. What is precipitated, and what is unchanged? When fully saturated with the gas, as indicated by the smell, filter. Which metal is on the filter and which is in the filtrate? Other reagents, as Na2CO3 solution, would precipitate the latter.

Experiment 112. -Put 1 or 2 pieces of P into an evaporating- dish, and pour over them 5 or 10cc.CS2 carbon disulphide. This will be enough for a class. When dissolved, dip pieces of unglazed paper into it, and hold these in the air, looking for any combustion as they dry. The P is finely divided in solution, which accounts for its more ready combustion then. Notice that the paper is not destroyed. This is an example of so-called "spontaneous combustion." The burning- point of P, the combustible, in air, the supporter, is about 60 degrees.

Combustion under Water.
Experiment 113
. -Put a piece of P in a test-tube which rests in a receiver, add a few crystals KClO3 and 5cc. H2O. Now pour in through a thistle-tube 1cc.or more of H2SO4. Look for any flame. H2SO4 acts very strongly on KClO3. What is set free? From this fact explain the combustion in water.

Experiment 114.--Put into a 20cc.flask 1 g. P and 50cc.saturated solution NaOH or KOH. Connect with the p.t. by a long delivery-tube, as in Figure 44, the end of which must be kept under water. Pour 3 or 4cc.of ether into the flask, to drive out the air. It is necessary to exclude all air, as a dangerously explosive mixture is formed with it. Heat the mixture, and as the gas passes over and into the air, it takes fire spontaneously, and rings of smoke successively rise. It will do no harm if, on taking away the lamp, the water is drawn back into the flask; but in that case the flask should be slightly lifted to prevent breakage by the sudden rush of water. On no account let the air be drawn over. The experiment has no practical value, but is an interesting illustration of the spontaneous combustion of PH3 and of vortex rings. What are the products of the combustion? An admixture of another compound of P and H causes the combustion.

Experiment 115.--Draw out into two parts in the Bunsen flame a piece of glass tubing 20cm long and 1 or 2cm in diameter. Into the end of one of the ignition tubes thus formed, when it is cool, put one-fourth of a gram of arsenic trioxide, As2O3, using paper to transfer it. Now put into the tube a piece of charcoal, and press it down to within 2 or 3cm of the AS2O3 (Fig. 45). Next heat the coal red-hot, and then at once heat the As203. Continue this process till you see a metallic sublimate- metallic mirror-on the tube above the coal. Break the tube and examine the sublimate. It is As. Heat vaporizes the As2O;3.

Tests.-Experiments 115 and 116 are used as tests for the presence of arsenic.
Experiment 116.--Prepare a H generator, - a flask with a thistle- tube and a philosopher's lamp tube (Fig. 46), put in some granulated Zn, water, and HCl. Test the purity of the escaping gas (Experiment 23), and when pure, light the jet of H. H is now burning in air. To be sure that there is no As in the ingredients used, hold the inside of a porcelain evaporating-dish directly against the flame for a minute. If no silvery-white mirror is found, the chemicals are free from As. Then pour through the thistle-tube, while the lamp is still burning, 1cc.solution of AS2O3 in HCl or H2O a bit of As2O3 not larger than a grain of wheat in 10 cc. HCl. See whether the color of the flame changes; then hold the evaporating-dish once more in the flame, and notice a metallic deposit of As. Set away the apparatus under the hood and leave the light burning. This experiment must not be performed unless all the cautions are observed, since the gas in the flask (AsH3) is the most poisonous known, and a single bubble of it inhaled is said to have killed the discoverer. By confining the gas inside the flask there is no danger. Instead of using As2O3 solution, a little Paris green, wall paper suspected of containing arsenic, green silk, or green paper labels, etc., may be soaked in HCl, and tested.

Formation of SiO2 from Sodium Silicate.
Experiment 117
.--To 5cc.Na4SiO4 in au evaporating-dish add 5cc. HCl. Describe the effect. Pour away any extra HCl. Heat the residue gently, above a flame, till it becomes white, then cool it and add water. In a few minutes taste a drop of the water, then pour it off, leaving the residue. Crush a little in the fingers, and compare it with white sand, SiO2.

Experiment 118.--Put into a test-tube 10cc. H2O and 2 or 3 g. NaOH. Note its easy solubility. Test with litmus. Will it neutralize any acids?

Experiment 119.--Pulverize and mix intimately 4 g. KNO3, l/2 g. S, 1/2 g. charcoal. Pile the mixture on a brick, and apply a lighted match. The adhering product can be removed by soaking in water.

Experiment 120.--With forceps hold a short strip of Mg ribbon in a flame. Note the brilliancy of the light, and give the reaction. Examine and name the product.

Experiment 121.--Burn a strip of Zn foil, and note the color of the flame and of the product. State the reaction. The red color of zincite is supposed to be imparted by Mn present in the compound.

Experiment 122.--Dissolve 2 g. of iron filings in diluted HCl. Filter or pour off the clear liquid, divide it into two parts, and add NH4OH to one part till a ppt. occurs. Notice the greenish color of Fe(OH)2. Oxidize the other part by adding a few drops of HNO3 and boiling a minute. Now add NH4OH, and observe the reddish color of the ppt., Fe2(OH)6.

Experiment 123.--Dissolve a few iron filings in dilute H2SO4, and slowly evaporate for a few minutes.

Experiment 124.--To 5cc. of water in a clean delivery-tube add the same volume of H2SO4, not C.P.; shake, and notice any fine powder suspended. PbSO4, being insoluble in water, is precipitated. What is the test for Pb? See Experiment 109.

Experiment 125.--Put a small fragment of Pb on a piece of charcoal, and blow the oxidizing flame against it for some time with a mouth blow-pipe. Note the color of the coating on the coal. PbO has formed.

Experiment 126.--Dissolve a small piece of lead in dilute HNO3. Pour off the solution into a test-tube and add HCl or other soluble chloride. Pb(NO3)2 + 2 HCl = ? What is the insoluble product?

Experiment 127.--Add to a solution of Pb(C2H3O2)2 some H2SO4. Give the reaction and the explanation.

Experiment 128.--Put 5 cc. AgNO3 solution in each of three test-tube To the first add 3 cc. HCl, to the second 3cc.NaCl solution, and to the third 3 cc. KBr solution. Write the reaction for each case, and notice that the first two give the same ppt., as in fact any soluble chloride would. Filter the second and third, on separate filter papers, and expose half the residue to direct sunlight, observing the change of color by occasionally stirring. Solar rays reduce AgCl and AgBr, it is thought, to Ag2Cl and Ag2Br. Try to dissolve the other half in Na2S2O3, sodium thiosulphate solution. This experiment illustrates the main facts of photography.

Experiment 129.--Put into a test-tube 20 g. of cannel coal in fine pieces. Heat, and collect the gas over H2O. Test its combustibility. Notice any impurities, such as tar, adhering to the sides of the test-tube, or of the receiver after combustion. Try to ignite a piece of cannel coal by holding it in a Bunsen flame. Is it the C which burns, or the hydrocarbons? Distil some wood shavings in a small ignition-tube, and light the escaping gas.

Experiment 130.--Introduce 20 cc.of molasses into a flask of 200 cc, fill it with water to the neck, and put in half a cake of yeast. Fit to this a delivery-tube, and pass the end of it into a test-tube holding a clear solution of lime water. Leave in a warm place for two or three days. Then look for a turbidity in the lime water, and account for it. See whether the liquid in the flask is sweet. The sugar should be changed to alcohol and CO2. This is fermented liquor; it contains a small percentage of alcohol.

Distilled Liquor.
Experiment 131
.--Attach the flask used in the last experiment to the apparatus for distilling water (Fig. 32), and distil not more than one-fifth of the liquid, leaving the rest in the flask. The greater part of the alcohol will pass over. To obtain it all, at least half of the liquid must be distilled; what passes over towards the last is mostly water. Taste and smell the distillate. Put some into an evapourating-dish and touch a lighted match to it. If it does not burn, redistil half of the distillate and try to ignite the product. Try the combustibility of commercial alcohol; of Jamaica ginger, or of any other liquid known to contain alcohol.

Effect on the System.
Experiment 132
.--Put a little of the white of egg into an evapourating-dish or a beaker; cover it with strong alcohol and note the effect. Strong alcohol has the same coagulating action on the brain and on the tissues generally, when taken into the system, absorbing water from them, hardening them, and contracting them in bulk.

Affinity for Water.
Experiment 133
.--To show the contraction in mixing alcohol and water, measure exactly 5cc.of alcohol and 5cc.of water. Pour them together, and presently measure the mixture. The volume is diminished. A strip of parchment soaked in water till it is limp, then dipped into strong alcohol, becomes again stiff, owing to the attraction of alcohol for water.

Experiment 134.--Weigh accurately, using delicate balances, 5 g. KClO3, and mix with the crystals 1 or 2 g. of pure powdered MnO2. Put the mixture into a test-tube with a tight-fitting cork and delivery-tube, and invert over the water-pan, to collect the gas, a flask of at least one and a half liters' capacity, filled with water. Apply heat, and, without rejecting any of the gas, collect it as long as any will separate. Then press the flask down into the water till the level in the flask is the same as that outside, and remove the flask, leaving in the bottom all the water that is not displaced. Weigh the flask with the water it contains; then completely fill it with water and weigh again. Subtract the first weight from the second, and the result will evidently be the weight of water that occupies the same volume as the O collected.

Experiment 135.--Weigh 5g, or less of sheet or granulated Zn, and put it into a small flask provided with a thistle-tube and a delivery-tube. Cover the Zn with water, and introduce through the thistle-tube measured quantities of HCl, a few cubic centimeters at a time. Collect the H over water in large flasks, observing the same directions as in removing O. Weigh the water, compute the volume of the gas, reduce it to the standard, and obtain the weight, as before. Should any Zn or other solid substance be left, pour off the water or filter it, weigh the dry residue, and deduct its weight from that of the Zn originally taken.

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