less opaque, and in the course of half or three-quarters of an hour vanishes altogether. As the cloud thus disappears, water is deposited upon the sides of the bottle, at first as a mere dew, but afterwards accumulating in droplets, which finally flow together to the bottom of When the air in the bottle has become clear, no antozone can be detected in it.

the vessel.

It thus appears that antozone has the property of taking up water in such a manner that the water assumes the peculiar physical conditions of a cloud or mist. While the antozone lasts the cloud is permanent; but the antozone is soon transformed into ordinary oxygen, and as fast as this change occurs the water of the cloud is deposited in droplets.

By passing the antozone mist through tubes filled with desiccating substances, such as chloride of calcium (Appendix, § 15), the water may be removed, and transparent antozonized air obtained, capable of again producing a mist on being brought in contact with water. Many strong saline solutions likewise deprive antozone of water; hence the non-appearance of the cloud when electrized air is passed through a strong solution of iodide of potassium; the cloud does appear, however, when the solution is sufficiently dilute.

It has been proved by experiment that electrized air can support or carry nearly twice as much moisture as ordinary air or oxygen at the same temperature, and that this air is much more difficult to dry than the gases with which chemists usually have to deal. This explains how it happened that, before the discovery of the cloud-forming property of antozone, so many observers had been led to consider ozone an oxide of hydrogen. One experimenter would pass recently electrized air through an ordinary drying-tube, such as long experience had shown to be capable of drying common air perfectly, and would then heat the gas; by this treatment both the ozone and the antozone would be changed to ordinary oxygen, and the water which had been carried through the drying-tube by the antozone would be made visible. The remarkable capacity of antozone for moisture being unknown, the water thus obtained was naturally enough supposed to have been derived from some compound of hydrogen and oxygen other than water, and capable of passing unabsorbed through the drying-tube. Other chemists, performing, as they supposed, the same experiment, but in reality operating upon air less recently electrized, and so containing no antozone, were, of course, unable

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to obtain any water at the point where it had been observed by their predecessors; hence arose a series of controversies which have only recently been composed.

180. As has been already mentioned, antozone, like ozone, is formed in all processes of oxidation and combustion. During combustion most of the ozone produced enters into combination with the substance burned, while the antozone is left free, or enters into combination with water to form peroxide of hydrogen. When the combustion is slow or smouldering, antozone appears in large quantities, and in presence of moisture forms the characteristic mist or cloud. Tobacco-smoke, the gray smoke of chimneys and of gunpowder, and all such smokes are antozone clouds, facts which support the idea that all clouds, fogs, and mists are caused by the presence of antozone in the atmosphere.

The oxidation of phosphorus affords a ready method of exhibiting the antozone cloud. During the oxidation of phosphorus in moist air, white fumes are formed, which were long a great puzzle to chemists. Whether the phosphorus be allowed to oxidize slowly, as in Exp. 75, or burned rapidly, as in Exp. 13, there is always produced a white mist of very considerable permanence, which remains long after the oxides of phosphorus, which are also formed, have been taken up and removed by the water. This mist is the antozone cloud; it is nothing but water held suspended by antozone.

In the rapid combustion of phosphorus, little or no ozone is left free; all of it seems to unite directly with the phosphorus; but much more antozone is produced when the combustion is rapid than when it is slow. The formation of antozone in this connexion explains the fact already alluded to (Exp. 13), that phosphorus burning with flame, in a confined volume of air, does not wholly exhaust the latter of oxygen. ine phosphorus cannot combine with antozone, but only with ozone; hence, when no oxygen other than that in the form of antozone remains, the combustion must cease.

During the burning of a jet of hydrogen under a bell-glass through which a stream of air is drawn, antozone is formed, as is proved by passing the issuing stream through water; the antozone cloud is produced without difficulty, and peroxide of hydrogen appears as a product. The formation of the antozone mist, and of peroxide of hydrogen, may be observed with any other flame if care be taken that the air which streams over the flame be not too strongly heated. A high temperature destroys the antozone as fast as it is formed.

152

ANTOZONE OXIDIZES WATER.

181. Besides its power of forming clouds or mists with water, which is interesting rather as a physical than as a chemical fact, antozone, particularly when newly formed, also unites with water chemically, the substance called peroxide of hydrogen (see § 61), whose composition is expressed by the formula H,O,, being the result of the combination.

A simple method of exhibiting the formation of peroxide of hydrogen by the action of antozone upon water, is to place a short, narrow tube, containing concentrated sulphuric acid, within a bottle 2 or 3 c.m. in width, furnished with a ground-glass stopper, and filled with water nearly to the top of the tube. Small portions of peroxide of barium are now added, at intervals, to the sulphuric acid in the tube, elevation of temperature being avoided as far as possible; the stopper should be replaced in the bottle after each addition of the peroxide. Most of the oxygen evolved in this process appears, however, to be in the ordinary inactive state, and the solution of peroxide of hydrogen obtained is consequently extremely dilute. A better method of procedure is to pass a current of carbonic acid gas into a mixture of water and peroxide of barium,

In this way a highly concentrated solution of the peroxide can be obtained.

Another easy method of preparing peroxide of hydrogen is by the oxidation of amalgams of lead or zinc. In this case also, as in the preceding, the peroxide of hydrogen is probably formed by the union of antozone with water.

One hundred grammes of lead-amalgam, containing so much mercury that it shall be fluid at the ordinary temperature, is shaken in a bottle of the capacity of a litre, together with 200 c. c. of water, acidulated with 2 grms. of sulphuric acid; the water soon becomes milky from separation of sulphate of lead, and in the course of ten or twelve minutes contains enough peroxide of hydrogen to exhibit the characteristic reactions of this substance.

So, too, if pulverulent zinc-amalgam be loosely thrown into a glass funnel, with narrow throat, and a thin stream of water be allowed to flow through it in such manner that the metal may be at the same time acted upon by both air and water, the water will become charged with peroxide of hydrogen. By repeatedly pouring back the dilute solution of the peroxide upon the amalgam, it can be very considerably strengthened. In order to prepare the zinc-amalgam, equal weights of zinc-filings and of mercury are placed in a beaker glass, covered with

DIFFERENCES BETWEEN OZONE AND ANTOZONE.

153

water acidulated with sulphuric or chlorhydric acid, and thoroughly mixed by stirring with a glass rod; the acid is then poured away, and the last portions of it removed from the amalgam by washing with

water.

This power of antozone to oxidize water distinguishes it completely from ozone, which has little or no action upon water.

182. Peroxide of hydrogen, like peroxide of barium, is supposed to contain one atom of oxygen in the form of antozone; the peroxides of potassium, sodium, and strontium also are placed in the same category. They are all called antozonides.

183. Antozone can be distinguished from ozone by the following tests:

Strips of paper, charged with a solution of sulphate of manganese (Exp. 77), do not become brown when exposed to the action of antozone; on the contrary, manganese papers which have been browned by ozone are bleached by antozone. Guaiacum paper (Exp. 78) does not become blue in antozonized air. The yellow compound called ferrocyanide of potassium, which is converted into red ferricyanide of potassium by the action of ozone, is not changed by antozone. In the absence of acids, antozone has no action upon iodide of potassium.

The chemical behavior of antozone may be conveniently studied by resorting to its compound with water, the antozonide peroxide of hydrogen. If peroxide of hydrogen be brought in contact with an ozonide like peroxide of lead, for example, both of the peroxides will be reduced, and there will result water, protoxide of lead, and free ordinary oxygen. Whenever an antozonide is mixed with an ozonide, a similar reaction occurs; the two active varieties of oxygen disappear, and common oxygen is evolved; hence it has been assumed that ordinary inactive oxygen is a sort of compound, resulting from the union or neutralization of ozone with antozone. Several important tests for antozone are dependent upon this fact of the decomposition of antozonides by ozonides.

If a liquid suspected to contain peroxide of hydrogen be shaken in a test-tube with a small quantity of ether, the ether will dissolve the peroxide, and will finally collect upon the surface of the liquid; on adding to it a small drop of a solution of the ozonide chromic acid, or, what comes to the same thing, a drop of a solution of bichromate of potassium acidulated with sulphuric acid, the ethereal solution will become blue.

If a liquid containing peroxide of hydrogen be added to a dilute red solution of permanganate of potassium, this solution will be decolorized,

while common oxygen will be evolved; and in the same way the brown peroxide of lead and the red-colored salts of peroxide of iron are bleached by it.

Another exceedingly delicate and characteristic test for antozone, or rather for peroxide of hydrogen, the rationale of which has not yet been well made out, is the following:-If to a solution containing peroxide of hydrogen there are added a few drops of dilute starch-paste charged with iodide of potassium, and subsequently a very small quantity of a solution of copperas (protosulphate of iron), iodine will be set free, and the starch will become blue. The solution to be tested must be as nearly neutral as possible. The addition of an acid, instead of the copperas solution, will also bring about the same reaction, though less readily.

184. We have thus set forth whatever is best known concerning ozone and antozone, in spite of the details into which so full an exposition has necessarily descended, partly because the subject will evidently be one of primary importance, both theoretical and practical, in the near future, and partly from a desire to show the student how vague and uncertain the prospect is when once the narrow limits of established knowledge are past and the inquirer ventures out into the obscurity which perpetually separates the knowledge of to-day from that which shall be knowledge to-morrow, but also because of the impossibility, with so obscure a subject, of making such a just discrimination between salient and unimportant points as with a well-studied subject is both easy and desirable.

CHAPTER XIII.

SULPHUR.

185. Sulphur occurs somewhat abundantly in nature, both in the free state and in combination with other elements. Many ores of metals, for example, are sulphur compounds. It is a component of several abundant salts, such as the sulphates of calcium, barium, and sodium, and occurs in small proportion in