192 Miscellaneous Lttelligence. 



Ox. Zinc 51.5 



Silica, 39.2 



Water, 6.4 



Ox. iron, .2 



97.3 

 The best inferences I can draw from these experiments are, 

 that the first of these substances is a compound of 



One atom of zinc, and 



One atom of sulphur, 

 with a mixture of arsenic and oxide of iron, which bears no 

 relative proportion, and may therefore be considered as extra- 

 neous ; and the second is a quaternary compound of 



One atom oxide of zinc. 



One atom of water, and 



Two atoms of silica, 

 and may therefore be considered as a hydrated bisilicate of 

 zinc. 



In the above statement of the atomic constitution of these 

 substances, I have considered the weight of the atom of zinc as 

 33, and that of its oxide as 41, but I by no means consider 

 these numbers as correct, for 1 have endeavoured during my 

 experiments on these minerals to determine the true weight of 

 the atom of zinc, but have never been able to obtain two re- 

 sults that agree nearer than 4 or 5 parts in 100, but if I took 

 the average of six or seven operations they give me as a mean 

 result 31.943. I conceive the difficulty to arise from the ten- 

 dency which zinc has to form triple salts with the alkalies, more 

 particularly with potash and ammonia, which renders the mode 

 of obtaining cadmium, recommended in a former Number of 

 your Journal, rather fallacious, unless great care is taken to use 

 none of the substances in excess, and I am not sure even then 

 whether it may be implicitly relied on, — at least it will not 

 succeed in my hands : for if to a solution of nitrate of zinc 1 

 add ammonia in excess to dissolve the oxide, and subsequently 

 a solution of potash, oxide of zinc will precipitate, (and so would 

 cadmium, if any was present) ; if the oxide of zinc is separated, 

 and the clear solution boiled, a triple salt will form, which is a 



