82 On Hydrate of Chlorine. [1823. 



were first instructed by Sir Humphry Davy, in his admirable 

 researches 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 tempera- 

 ture of 40 Fahr. 



M. Thenard, in his ' Traite 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 intro- 

 ducing 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 octahedra, 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 ; 



