1839.] 



On Chemical Tests, 



341 



sulphate of cadmium, sulphate of copper, sulphate of silver; it does not 

 precipitate nitrate of cobalt, sulphate of manganese. 



Sulphuret of silver does not precipitate acetate of lead, nitrate of co- 

 balt, sesquichloride of iron, sulphate of cadmium, sulphate of copper, 

 sulphate of manganese, nitrate of nickel. 



It will be observed on examination that sulphuret of manganese de- 

 composes all the solutions of metallic oxides tried, while the sulphuret 

 of silver did not decompose any one whatever ; it results from these 

 facts that if silver has the strongest and manganese the weakest affi- 

 nity for sulphur, all the other metals are intermediate as to these, and 

 arranged according to their degrees of affinity for sulphur ; they stand 

 thus : silver, copper, lead, cadmium, iron, nickel, cobalt, manganese. 



The metals are here so arranged that any one of them in state of 

 sulphuret does not act upon a solution of the metals following: thus 

 for example, the sulphuret of nickel precipitates the salts of silver, 

 copper, lead, cadmium and iron, but effects no change in those of cobalt 

 and manganese. 



There is only one exception, it is that the sulphuret of iron precipi- 

 tates the nitrate of lead, whilst the sesquichloride and pernitrate of 

 iron are only partially precipitated by the sulphuret of lead. London 

 and Ed. Journal, V age 138. 1838. 



Sulphurets, may be detected, some by fire which drives off the sul- 

 phur : and those soluble in water, by being treated with muriatic or 

 sulphuric acid, which disengages sulphuretted hydrogen, and if the 

 solution be not too dilute, effervescence occurs. This gas may be known 

 by its smell, or by its tarnishing silver. Or the sulphuret may be pul- 

 verized and digested with strong nitric acid ; this converts the sulphur 

 into sulphuric acid, which may be detected by a solution of barytes, 

 or of lead. 



118. TAN, or tannin is employed for detecting animal gelatine, or 

 jelly, with which it forms an elastic adhesive mass, that soon dries in 

 the open air, and becomes converted into a brittle resinous-like sub- 

 stance, insoluble in water, and capable of resisting a great number of 

 chemical re-agents. It resembles overtanned leather. Tan also acts 

 on albumen, but the precipitate does not take place immediately 

 with gelatine an immediate precipitate occurs. A solution of tan may 

 be made by pouring hot water on bruised gall-nuts, or oak-bark, cate- 

 chu, &c, and allowing the infusion to stand some time, filtering it when 

 it becomes cold. 



a. If corrosive sublimate does not act on the liquid under exami- 

 nation the absence of albumen may be inferred with certainty. Then 



