Page:Experimental researches in chemistry and.djvu/97

82 first instructed by Sir Humphry Davy, in his admirableresearches into the nature of that substance, published in the Philosophical Transactions' for 1810–11, that the solid body obtained by cooling chlorine gas, was a compound with water; and that the dry gas could not be condensed at a temperature equal even to -40° Fahr., whilst on the contrary, moist gas, or a solution of chlorine in water, crystallized at the temperature of 40° F ahr.

M. Thénard, in his 'Traité de Chimie,' has described the deposition of the hydrate of chlorine by cold from an aqueous solution of the gas. It forms crystals of a bright yellow colour, which liquefy when their temperature is slightly raised, and in so doing give off abundance of gas.

This substance may be obtained well crystallized, by introducing into a clean bottle of the gas, a little water, but not sufficient to convert the whole into hydrate, and then placing the bottle in a situation the temperature of which is about or below freezing, for a few days: and I have constantly found the crystals better formed in the dark than in the light. The hydrate is produced in a crust or in dendritical crystals; but being left to itself, will in a few days sublime from one part of the bottle to another in the manner of camphor, and form brilliant and comparatively large crystals. These are of a bright yellow colour, and sometimes. though rarely, are delicate prismatic needles extending from half an inch to two inches into the atmosphere of the bottle: generally they are of shorter forms, and when most perfect and simple, have appeared to me to be acute flattened octahedral, the three axes of the octahedron having different dimensions.

Though a solution of chlorine deposits the hydrate when cooled, yet a portion remains in solution, and the crystals also dissolve slowly in water. It is therefore soluble, though not so much so as chlorine gas. When a solution of chlorine is cooled gradually till the whole is frozen, there is a perfect separation of the hydrate of chlorine from the rest of the water, or rather from the ice; for crystals of ice, formed in a solution of chlorine, when washed in pure water, and then dissolved, do not trouble nitrate of silver.

I neglected to ascertain the specific gravity of the crystals whilst the weather was cold and they were readily obtainable;