Chemical History of Mercury. 295 



the facility with which it oxidizes and acidifies its elements, is re- 

 markable ; and it deserves notice, that when the black prolosulphu- 

 ret of mercury (obtained by precipitation from the protonitrate by 

 sulphuretted hydrogen) is boiled with that acid, that it is speedily 

 decomposed and entirely converted into nitrate of mercury, and not 

 a particle of cinnabar is separated, which probably would be the 

 case if M. Guibourt's view of its composition were correct. 



§ III. Of the Chlorides of Mercury. 



It is now universally admitted, that calomel and corrosive subli- 

 mate are chlorides of mercury ; that calomel, or the protochloride, 

 consists of one proportional of mercury se 200, and one of chlorine 

 = 36 ; and that corrosive sublimate, or the perchloride, consists of 

 one proportional of mercury = 200, and two of chlorine = 72 : the 

 equivalent or representative number therefore of the former, is 236, 

 and of the latter 272. 



In some inquiries connected with the preparation of calomel 

 upon the large scale, conducted in the laboratories at Apothecaries' 

 Hall, Mr. Hennell has discovered several curious and important 

 facts respecting the chlorides of mercury, more especially in 

 relation to the triple compounds formed by corrosive sublimate 

 with other chlorides. He has ascertained that certain chlorides 

 which appear to have no action upon calomel at common tempera- 

 tures, decompose it at a boiling heat, to a greater or less extent, 

 and resolve it into corrosive sublimate and metallic mercury*. 



This action he has particularly investigated in respect to common 

 salt and muriate of ammonia, those being the substances usually 

 employed for the purpose of washing calomel, under the idea of 



• Since writing tlie above, the following note has been received from 

 Mr. Hennell : — 



" I had repeatedly noticed a bluish tint which calomel acquires when washed 

 in a boiling solution of muriate of ammonia, as directed by the London 

 Pharmacopoeia, to remove corrosive sublimate. To ascertain the cause, I 

 boiled 100 grains of pure calomel in a solution of muriate of ammonia, con- 

 taining 100 grains of the salt. The change of colour in a few minutes was 

 very evident. The solution, when tested, contained corrosive sublimate. The 



