44S Preparations and Compositions. Part III.

i

I ■

h

These processes, which are essentially the same, are intend-ed to furnish a substitute for the black oxide of quicksilver, onwhich the efficacy of the mercurials most frequently employed,and most certainly useful, depends. In these, the mercury isoxidized by trituration, in contact with the atmosphere; butthe operation is both so tedious and troublesome, that it is of-ten imperfectly performed, or assisted bj r improper means.

In the processes we are now explaining, it was supposed,that, as ammonia has a stronger affinity for nitric acid thanoxide of mercury has, it would separate oxide of mercury fromits solution in nitric acid ; and, therefore, that the precipitateobtained was oxide of mercury, similar to that formed by tri-turation. But, since the nature of the triple metallic salts hasbeen better understood, this has been discovered to be an er-ror. The grey precipitate which is formed may, generallyspeaking, be called a subnitrate of mercury and ammonia;for it consists of oxide of mercury and ammonia, not saturatedwith nitric acid; but, even to ocular inspection, it does notseem to be homogeneous; and, when it is digested in aceticacid, it is partially dissolved, and the residuum acquires a verypale, or almost white colour. The portion dissolved seems tobe black oxide, and the white residuum to be pure subnitrateof mercury and ammonia, which, according to Fourcroy,crystallizes in brilliant polyhedral crystals, without smell, ofan extremely styptic taste, scarcely soluble in water •, is de-composed by heat, by the sulphuric and muriatic acids, andby lime, potass and soda ; and consists of 68/20 oxide ofmercury, 10 of ammonia, and 15.80 of nitric acid. Ac-cording to these observations, this preparation ought not tobe called the grey oxide of mercury, and is not identical withthe black oxide of mercury prepared by trituration. If, how-ever, it answered the same purposes, the identity would be oflittle consequence; but, from its never having been introducedinto general use, although so much more easily prepared, \remay presume that it is not equal in point of efficacy.

Black oxide of mercury may, however, be obtained, accord-ing to the direction of Saunders, now adopted by the Londoncollege, by tritmaring with lime-water, and subsequent edul-coration, the sublimed submuriate of mercury, or rather theprecipitated submuriate, as proposed by Gottling ; and thatthe decomposition may be more easy and complete, I maysuggest, that for this preparation the latter submuriate shouldnot be dried, but should be triturated with the lime-water assoon as it is edulcorated. This simple black oxide certainlymerits a fair trial.