This phenomenon (of turning the paste of iodide of potassium blue) takes place in the same manner whether the point emit positive or negative electricity; it is also perfectly immaterial of what substance the point is made, if only an emission of electricity occurs, thus refuting the view of those earlier physicists who maintained that the odor was owing to metallic particles carried off by the issuing electricity.

On holding a platinum or gold plate before the point while the machine is turned, the plate has imparted to it negative galvanic polarization, which can be demonstrated in the following manner:

Fig. 83.

Connect the two mercury cups a and b, Fig. 83, with the wire ends of a multiplier. Into the cup a dip a copper wire, to the other end of which a platinum plate p is fastened, the plate having been first soldered with gold to a platinum wire, and this to the copper wire at n. This platinum plate hangs in a glass vessel containing water slightly acidified.

After having exposed a perfectly similar platinum plate for a time to the electricity issuing from a point, immerse it also in the water of the glass vessel, and as soon as the copper wire of the second plate is immersed into the cup of mercury b, a considerable

n

divergence of the galvanometer needle takes place, and in a direction which indicates that the platinum plate which had been exposed to ozone behaves negatively toward the other; that is, the deflection is in the same direction which would have been indicated had a zinc wire been placed in a, a copper wire in b, and these wires then immersed in the liquid of the glass vessel. This current, however, is only

transient.

The whole subject of galvanic polarization we will discuss in another place; it is only mentioned here as one of the effects which accompany the emission of electricity from points.

All these reactions disappear when sulphuretted hydrogen, ammonia, olefiant gas, &c., are diffused in the air of the room where the experiment is made.

If the emitting point be raised by the flame of a spirit lamp to a red heat, and the machine put in operation immediately after the removal of the lamp, all the above described phenomena, which had accompanied the escape of electricity, disappear; that is, the electrical odor is no longer perceived, the iodine preparation does not turn blue, platinum or gold plates are not polarized. All the phenomena reappear, however, gradually, as the point cools.

In order to make the experiment distinct, with reference to the odor, it must be made with wires of one of the precious metals, because the easily oxidable metals diffuse a peculiar smell simply by being heated. Very thin wires are not suitable for this experiment; but as thick

* See report for 1855, p. 377.

ones may not always be at hand, it will do to use a thin platinum wire having its end fused into a small knob about one line in diameter.

§ 96. Electrical odor in the electrolysis of water.-The electrical odor appears not only on the escape of electricity from points, but also in the electrolytic decomposition of water, where we find it accompanied by the same reaction and effects which were considered in the preceding paragraph.

On closer investigation it appears that electrical odor manifests itself at the positive pole, where oxygen is given off; for on collecting the gases resulting from the decomposition of water separately, the odor in question was perceived only in that vessel which contained the oxygen, no trace of it being found in the one containing the hydrogen. The gases when obtained together have the electrical odor.

On suspending a paper covered with the paste of iodide of potassium in oxygen, or in the mixed gases to which the ozone odor has been imparted by electrolysis, the paper turns blue. A platinum plate exposed for a time to the action of this, gas indicates the same electro-negative polarization as though it had been acted on by the

electrical brush.

Chemically pure oxygen gas produces none of these effects; it has not the odor, does not turn the iodide paste blue, and is not in the condition to polarize a platinum plate negatively.

The gas obtained by electrolytic decomposition produces, in all these cases, the same effects as the air which issues from a strongly electrified point.

§ 97. Production of ozone in the chemical way.-The so-called electrical odor can be produced by purely chemical means without any aid from electricity. A piece of phosphorus made perfectly dry by blotting paper, so that it has a clean surface, emits a peculiar alliaceous odor. Placing such a piece of phosphorus in a jar of air, the vapor of phosphorus will in the cold soon diffuse itself through the whole jar. A platinum plate being then suspended in the jar a short time it will be polarized positively.

The polarization of the platinum plate is to be ascribed to the phosphoric vapor diffused in the jar, but the odor very probably is due to the phosphoric acid, which is formed by the partial oxidation of the phosphorus vapor.

If a little water be now introduced into the jar, (as much as will half cover the piece of phosphorus,) the phosphoric odor becomes weaker and weaker, and at length wholly disappears, and in its place a decided ozone odor will be perceived. At rather high temperatures the ozone smell appears very soon.

This odor is not to be distinguished from that produced in the electrical way, and it is accompanied by all the reactions and effects which characterize the agency of the electrical odor. A paper with the iodide paste on it becomes blue when suspended in the jar, and a platinum plate exposed to its action is polarized electro-negatively.

With the ozone obtained in the chemical way the reactions can be produced almost exactly in the same form as with a point emitting electricity. For this purpose a bottle of the capacity of several quarts

Fig. 84.

is filled with air containing ozone, and closed with a cork, (Fig. 84.) having two holes bored in it. Through one of the holes a tube passes nearly to the bottom, having a funnel at its upper end; through the other hole a tube passes, which merely goes through the cork, and above the cork is bent horizontally, ending in a tolerably fine opening; water being poured through the funnel in a regulated stream, the air containing the ozone is driven out through the point of the other tube. This point now behaves exactly like a metallic point from which an electrical brush issues. By holding the nose to it the electrical odor will be observed; the iodide paper held before it turns blue, and a platinum plate exposed to the jet is polarized electro-negatively.

We have seen above that all the effects of ozone disappear when the point emitting the brush is heated, in like manner all the re

actions of ozone disappear as soon as the horizontal part of the escape tube is strongly heated by a spirit lamp. The air which escapes from the opening of the hot tube has no longer any smell, it will not turn the iodide paper blue, nor polarize the platinum plate. But all these effects reappear on the cooling of the tube.

$ 98. Chemical nature of ozone.-Schönbein, the discoverer of ozone, has observed and investigated for years, with unwearied industry, the relations of this remarkable substance, and has found that it bears the greatest resemblance to the hyper oxides; he has finally come to the opinion that ozone is nothing else than a gaseous peroxide of hydrogen.*

Ozone is therefore formed by a further oxidation of the vapor of water contained in the air. Thus it is explained why water, or rather the vapor of water, is absolutely necessary to the formation of ozone. In perfectly dry air ozone cannot be obtained by means of phosphorus. Electricity prepares the vapor of the atmosphere to oxidize further

At the present time, however, the view of nearly all of the chemists who have studied this subject is different from that given by the author. It is now generally conceded that ozone is nothing but oxygen, but there are two different views in regard to its nature; according to one, ozone is simply oxygen thrown into a condition of activity by the instrumentality of electricity or other agents above named.

The other view considers ozone as formed of two or more equivalents of oxygen. If, as some hold, gaseous oxygen be o,, it could be easily shown that this double molecule undergoing decomposition, (even by reducing agents as phosphorus, the essential oils, &c.,) sets free 01, (oxygen in the nascent state,) which might unite with o, to form O'o,, similar in properties to S o,, (sulphurous acid,) sulphur and oxygen being elements capable of replacing each other to form analogous compounds as in the sulphurets and oxides.

We deem it moreover quite possible, in a measure, to reconcile the views of Schönbein with those last named, but this whole subject, being a purely chemical question, would be out of place in a report upon physical science, and has only been mentioned because the bare statement in the text might lead those not familiar with the matter into erroneous views. G. C. S.

and form ozone; in like manner phosphorus effects the combination of the vapor of water with oxygen, but, as yet, we are not able to tell how it is done.

Ozone is decomposed into its components, oxygen and hydrogen, by heat, as shown by the experiment noticed above.

De la Rive and Berzelius, indeed, regarded ozone as modified oxygen, and maintained that it could be produced by an electrical jet in dry oxygen, but this is contrary to all Schönbein's analogies. Schönbein presented the following experiment as the most striking proof of the presence of hydrogen in ozone: if air containing ozone be dried as perfectly as possible and then heated, it yields water on cooling to hydroscopic bodies over which it is passed. The ozone is decomposed by heat, and the vapor of water which it contained is set free.

Ozone is one of the most powerful means of producing oxidation which is known. Air containing ozone being passed for a long time over finely divided metallic silver, the latter is converted into peroxide of silver. The vapor of phosphorus is rapidly oxidized under the influence of ozone, and converted into phosphorous acid and phosphoric

acid.

The fact that the passage of the electrical spark through moist atmospheric air forms nitric acid was discovered by Cavendish, in the year 1785. Schönbein has proved that under like circumstances ozone also is always formed.

Since ozone can be produced in moist oxygen by the help of the electric spark, it is evident that the formation of ozone is independent of that of nitric acid. On the contrary, Schönbein has made it appear highly probable that the formation of nitric acid is not a direct effect of electricity, but a secondary effect produced by the oxidizing influence of ozone on the nitrogen of the atmosphere.

The formation of nitric acid by electricity may be shown in the simplest manner, by exposing, for a time, a paper moistened with a solution of carbonate of potash to a jet of electricity escaping from a wire; the carbonate, under these circumstances, is converted in part into nitrate of potash.

The ozone formed by means of phosphorus also produces nitric acid. The mixture of phosphorous and phosphoric acids, which forms in a receiver containing a piece of phosphorus, water, and atmospheric air, is absorbed by water. If this water be colored by a solution of indigo, the color of the latter is immediately destroyed, an effect which neither phosphorous nor phosphoric acid alone can produce. The decoloring is effected by a small quantity of nitric acid, which, formed under the influence of the ozone, is also dissolved in the water.

That it is actually nitric acid which is here in question is proved by shaking the water with milk of lime; insoluble salts of lime are formed with the phosphorous and phosphoric acids, while a nitrate of lime remains in solution.

Davy observed that traces of nitric acid appeared at the positive pole of a pile when a voltaic current passed through water containing air or nitrogen. Here, also, the formation of nitric acid is a secondary effect

of electricity. Ozone is first formed by the action of the current, and the ozone then oxidizes the nitrogen.

§ 99. Illumination of phosphorus produced by ozone.-It is well known that at low temperatures, slow combustion of phosphorus does not take place in air free from ozone, and there is therefore no illumination in the dark; this, however, appears as soon as ozone is brought into contact with the phosphorus. In a receiver containing ozonized air phosphorus shines at a very low temperature.

Schönbein has shown this very beautifully by presenting a stick of phosphorus, at a low temperature, to an electrical brush, which, in accordance with the above, determines the formation of ozone. manner in which the experiment was made is as follows: (Pog. Ann., lxviii, 38.)

The

A piece of phosphorus an inch long, having a clear surface, was placed on a board in conducting connexion with the earth, and the free end of a wire, connected with the conductor of an electrical machine, brought within a few lines of the phosphorus. At a temperature of -2° the phosphorus by itself did not shine in the dark; but when the machine was put in motion, so that an electrical brush played against the piece of phosphorus, a light flame at once issued from its whole length, and, like the tail of a comet, extended far beyond the piece of phosphorus. If the machine be stopped the illumination of the phosphorus ceases in a few seconds.

Schönbein obtained a very beautiful illumination by the following arrangement: A copper wire was coiled around a stick of phosphorus an inch long, so that the end of the wire extended about a line beyond the phosphorus, as shown in fig. 85. The

other end of the wire is connected with the conductor of an electrical machine. At a temperature below 0° the phosphorus did not shine at all in the greatest darkness;

Fig. 85.

but in turning the electrical machine, so that a strong brush appeared at the end of the coil, a luminous cone protruded from the middle of the brush, which attained a length varying from a few inches to some feet, according to circumstances. The longest cone obtained by Schönbein was 2 feet. With powerful machines such cones should be obtained of still greater length.

It may be assumed without hesitation that this luminous train is nothing else than the vapor of phosphorus in slow combustion. The luminous train vanishes with the electrical brush.