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The delivery-tube of the bottle should be connected with a jar over the water-trough, in order that no chlorine may escape into the room. The chlorine water thus prepared may be put in the larger cylinder (No. 2), inverted in a soup-plate of water, and set in the sunshine.

6. ($ 2, Exp. 3.) Fill one of the jars (No. 3) with oxygen, and let it stand over the trough long enough to drain. Burn the hydrogen as it escapes from the generator (No. 11) through a glass tube bent at right angles and drawn out to a fine jet; and hold the jar of oxygen over the flame.

Glass tubing may be bent by heating it red-hot in the flame of the lamp. A tube may be drawn out to a fine jet by heating the middle red-hot, and then quickly pulling the ends apart. It may be cut by scratching it a little on one side with a threecornered file, and then bending it over the thumb-nails, held close together on the side opposite the scratch.

7. ($ 3, Exp. 1.) Fill chlorine tube (No. 12) with chlorine over the water-trough. Close the mouth while under water with the thumb, invert it, and insert the cork. Pour a little strong ammonia into the funnel, and let it drop slowly into the tube by means of the nipper-tap, to the depth of half an inch. Close the nipper-tap, and pour off the ammonia from the funnel; and then fill the funnel with water, and let it run into the tube, care being taken to keep water in the funnel all the time, so that no air may get into the tube.

In this and all other cases where chlorine is to be used, it will be best to prepare it beforehand, and keep it in a gas-bag till wanted. On its way from the generating flask to the gas-bag, it should be passed through a wash-bottle containing a small amount of water. The gas is washed to remove any muriatic acid which may be in it, and which would corrode the bag.

8. (§ 6, Exp. 1.) Fill the bent tube in the first place with water, close it with the thumb, and invert it over water. Then allow a little hydrogen to pass into it from the generator, and also some oxygen from a gas-bag which has been previously filled with this gas. With a little care, one can readily get the right proportions. The tube should not be more than twothirds full of the mixed gases, and a considerable excess of one

gas should be used, so that enough may be left for testing. After putting the gases into the tube, close it with the thumb, raise it from the water, and tip it so that the gases may pass into the closed arm; then pour out a little of the water, and again close it with the thumb. Connect the outer coating of a charged Leyden jar with one of the platinum loops, by means of a wire or chain, and bring the knob of the jar in contact with the other loop. After the spark has passed, again fill the open arm with water, close it with the thumb, and tip the tube so as to transfer the remaining gas to the open arm, and there test it.

9. ($ 10, Exp. 1.) As explosions sometimes occur in the manufacture of oxygen, care should be taken that the chemicals are pure; and it would be well to test each purchase by putting some of the potassic chlorate in an iron spoon and heating it over a spirit lamp until it is melted; then stir into it with an iron wire some of the black oxide of manganese; and if these materials are not good, an explosion will take place, and a whitish mass with red spots in it will be left in the spoon. If, however, the chemicals are pure, there will be no explosion, and the melted mixture will soon dry up, leaving a dark gray residuum. If the bubbles come over too violently, remove the lamp for a few minutes until they come more moderately.

A glass flask may be used; but as it is liable to break, a copper flask may perhaps be found cheaper in the long run, especially if one has to make oxygen often.

10. ($ 11, Exp. 1.) Use glass jar (No. 3). The charcoal may be fastened to a piece of wire and ignited in the flame of a lamp. It is well to have the other end of the wire attached to a copper or wooden disk, which serves to cover the jar while the charcoal is burning.

Lime-water may be made by putting a small quantity of slaked lime into a jar (No. 3) of water, stirring it thoroughly, and allowing it to settle. The clear liquid may then be poured off into a bottle, and kept for use.

II. ($ 11, Exp. 2.) Fill a jar (No. 3) with oxygen, and let it stand to drain. Put a piece of sulphur in the chalk cup (No. 16), ignite it by touching it with a red-hot wire, and invert a jar of oxygen quickly over it. The jar should be kept closed

with the plate until it is inverted, and brought just over the sulphur. The chalk cup should stand in a shallow dish of water, so that the mouth of the jar may dip under the water and prevent the SO2 from escaping into the room.

12. ($ 11, Exp. 3.) The phosphorus may be burnt in the same way as the sulphur. As phosphorus is a very inflammable substance, and as burns from it are very slow to heal, great caution must be exercised in using it. The sticks must always be cut under water, and it must be carefully dried, by pressing it between pieces of unsized paper, before it is burnt; else it will fly about in a very disagreeable and dangerous manner. It should always be lighted by touching it with a heated wire, never by holding it in the flame of a lamp.

13. (§ 11, Exp. 4.) The watch-spring should be either straightened out or formed into a spiral, and fastened to a disk of copper or wood, as above described. Water should be left in the bottom of the jar to the depth of two inches or so, that the melted globules of iron may not burn into the jar.

14. ($ 12, Exp. 1.) Ozone may be most easily prepared by pouring a little ether into a jar (No. 3), and then when the air in the jar has become saturated with the vapor of ether, stirring the air with a glass rod heated nearly to redness.

15. ($ 20, Exp. 1.) In making hydrogen, use the hydrogen generator (No. 11).

16. ($ 21, Exp. 1.) Mix the gases in the gas-bag, letting each gas pass in separately. The quantities can be estimated nearly enough by the eye. Fasten an ordinary clay tobacco-pipe to the gas-bag, hold the mouth of the pipe in soap-suds, and press out the mixed gases in a gentle stream. For obvious reasons, the nipper-tap should be closed before the bubbles are lighted.

17. ($ 28, Exp. 1.) Fill the bottle generator (No. 6) onethird full with strong ammonia, and connect the large tube with a rubber bag filled with chlorine. Connect the delivery-tube with the wash-bottle (No. 17), and the delivery-tube of the washbottle with the larger cylinder (No. 2). Force the chlorine through the apparatus by compressing the bag. Care must be taken not to force an excess of chlorine through the ammonia,

lest the very explosive nitric chloride (page 28) be formed. There is little danger, however, if sirong ammonia is used.

18. ($ 30, Exp. 1.) Use the bottle generator (No. 6). First pour in water enough to cover the bits of copper (brass or nickel will do as well), and then pour in gradually strong nitric acid. The gas is very poisonous, and should not be allowed to escape into the room.

19. ($ 30, Exp. 2.) The management of the experiment is the same as in the burning of phosphorus in oxygen (12).

20. ($ 30, Exp. 3.) The gases may be mixed in a gas-bag. It is not necessary that the proportions should be exact.

21. ($ 33, Exp. 1.) Use nitric-oxide bell and jar (No. 18). Fill the bell with oxygen, and the jar with nitric

Fig. 36. oxide. The jar should be closed with a plate and set on the table, and the bell of oxygen set on the plate covering the jar (Figure 36). When the experiment is to be tried, the plate should be drawn out, and the mouths of the bell and jar allowed to come together.

22. ($ 36, Exp. 1.) Use tubulated retort (No. 20). Only a small quantity of the ammonic nitrate need be used. The retort must not be heated too much, lest gas should come off with explosive violence.

23. ($ 37, Exp. 1.) Gases, like ammonia and muriatic acid, which are absorbed by water, must be collected over mercury.

For the experiments of this book we think a mercury-trough a needless luxury. An evaporating dish of Berlin porcelain answers every purpose. One five inches in diameter is large enough to use with the cylinders mentioned above. It should be set in a shallow dish of strong glass or earthen ware, to prevent loss of mercury in case of accident. It should then be filled nearly full of mercury. The cylinder to be used is next filled with mercury to the brim. The ground-glass cover is then placed on the mouth of the cylinder and held firmly with the right hand, the cylinder inverted, and its mouth plunged beneath the mercury in the evaporating dish. It is well to put the cylin

over.

der in a strong dish when you are filling and inverting it, to save any mercury which may be spilled. After the cylinder is filled and inverted over the mercury in the dish, the plate is slipped from its mouth, and the cylinder is securely fastened in the clamp of a retort-stand, so that its mouth is held about for & of an inch above the bottom of the dish.

To fill the cylinder with ammonia gas, a little aqua ammonia is put into a flask provided with a delivery-tube, and gently boiled. To the delivery-tube is attached a piece of rubber tubing to connect it with the cylinder. A short piece of glass tubing with its end slightly turned up must be fastened to the end of the rubber tube, so that the gas may be introduced into the cylinder through the mercury. On first boiling the aqua ammonia, a large amoụnt of air passes over from the flask. The ammonia gas must not be collected until this has all passed

To determine when this has taken place, put the glass tube at the end of the rubber tube into a vessel of water; when heat is first applied to the flask, bubbles of gas will rise from the end of the tube through the water as long as any air comes

When the air is all over, the ammonia gas is absorbed by the water as fast as it comes over, and no bubbles rise to the surface. After the air ceases to come over, plunge the end of the glass tube into the mercury, and introduce it under the mouth of the cylinder. The gas will rise into the jar and displace the mercury.

When the cylinder is filled with ammonia, close it with a glass plate, and remove it to a vessel of water; then open the mouth of the jar under the water (Figure 37).

24. (§ 43, Exp. 1.) The oxalic acid may be heated with sulphuric acid in a flask, and the solution of soda put in a wash-bottle.

25. ($ 45, Exp. 1.) In both experiments, the sulphur should be heated cautiously, that it may not

over.

Fig. 37

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