236 Mr. Brett*s Analysis of some 



haloid salt, viz. bicyanide of mercury, is constant, and pro- 

 bably plays the part of an electro-negative or acid element ; 

 whilst the other haloid salt, viz. a chloride, varies, and probably 

 is electro-positive or basic; a mode of regarding the consti- 

 tution of such salts propounded by Caillot. These salts are 

 remarkable for the silky lustre which they possess, and this 

 feature is more strongly marked in those which contain po- 

 tassium as an element than in any of the others, and is best 

 observed in crystals obtained from their alcoholic solutions. 



The Chloro-cyanide of Ammonium and Mercury, 



If we dissolve in water 1 3 parts by weight of sal-ammoniac 

 with 60 parts of bicyanide of mercury and evaporate the solu- 

 tion, we obtain after a time a salt, which crystallizes in flattened 

 quadrangular prisms, possessing a somewhat silky lustre when 

 dry: if a solution of the salt be evaporated to a small bulk, it 

 crystallizes upon cooling in small prisms of the same form as 

 those obtained by a more gradual evaporation. This salt un- 

 dergoes fusion by heat and is decomposed, ammonia and 

 hydrocyanic acid being evolved. Alcohol is capable of dis- 

 solving this salt. When simply mixed in the cold with the 

 mineral acids, it does not appear to suffer decomposition ; when 

 heated for some time with them its decomposition is effected. 



In order to ascertain its atomic constitution, which analogy 

 and the proportions used in its preparation would lead us to 

 regard as an atom of each of its ingredients, the following 

 plan was adopted. 



Ten grains of the salt carefully dried over a sand-bath 

 were dissolved, in water, and a current of sulphuretted hydro- 

 gen passed through the solution; the whole was then, after 

 being boiled for a short time, thrown upon a weighed filter, 

 and the latter with its contents well washed, the washings be- 

 ing added to the filtered fluid: the bisulphuret of mercury 

 thus obtained was black, and when dry weighed 7'3 grains 

 = 7*94 grains of bicyanide. The quantity of bisulphuret of 

 mercury, by calculation, assuming the salt to be compounded 

 of 1 atom of each of its ingredients, is 7*599 = 8*26 grains of 

 bicyanide. 



The filtered fluid with the washings was kept for some time 

 exposed to the temperature of boiling water in order to get rid 

 of sulphuretted hydrogen; it was then mixed with a slight ex- 

 cess of caustic potass ; the whole was then evaporated to dry- 

 ness, ignited, and redissolved in water; the aqueous solution 

 was then precipitated by nitrate of silver, rendered acid by 

 means of nitric acid. The precipitated chloride was washed, 

 dried, and fused; it weighed 4*5 grs. = 1*68 of chloride of 



