1825.] Method of analyzing Sulphate of Zinc, 369 



with a few drops of hydrosulphuret of ammonia, and the mixture 

 left to digest for 24 hours in a very moderate heat. On exa- 

 mining the flask containing this mixture next day, I observed 

 a deposition of a few dark coloured flocks ; the supernatant 

 liquid was drawn off with a syphon, and the flask again filled 

 with distilled water. Next day the liquid was again drawn off 

 and fresh distilled water poured in ; this process was repeated 

 till the water drawn off had become pure ; the precipitate was 

 now dried and exposed to a red heat in a glass capsule ; in 

 this state it weighed 0*9 grain : it had a yellow coloui', was 

 tasteless and fixed in the fire. Being digested in nitromu- 

 riatic acid it slowly dissolved, leaving a portion of sulphur. 

 The solution was precipitated white by muriate of barytes, 

 and in white gelatinous flocks by prussiate of potash. Hence 

 it consisted of sulphuric acid and oxide of zinc. From this it 

 is obvious, that the yellow matter was sulphuret of zinc ; and 

 it must have contained the equivalent of 0*65 grains of oxide 

 of zinc. 



(8.) If we collect all the oxide of zinc obtained in these 

 difterent processes, we shall find them as follows : 



(jrains. 



From the carbonate 20*37 



Thrown down by boiling 4*54 



Obtained bjr evaporating to dryness. 0*431 



From the silicate of zinc 0*22 



From the sulphuret of zinc 0*65 



Total 26-211 



Now 26*211 divided by 5, gives 5*245 for the quantity of 

 oxide of zinc contained in 18*125 grains of sulphate of zinc. 



According to this determination, the atomic weight of oxide 

 of zinc is 5*245 ; this, I am persuaded, is about --gL^th part 

 below the truth ; I believe that in the preceding analysis I 

 lost 0*039 grain of oxide of zinc, which constituted about -g-fy 

 part of the whole. The loss I conceive to be owing to th& 

 want of a substance capable of precipitating the whole of the 

 oxide of zinc from its solution in sulphuric acid. Carbonate of 

 soda does not throw it down completely ; and I can affirm from 

 experiments made with care, that hydrosulphuret of ammonia 

 likewise acts imperfectly. 



My experiments, though numerous, never gave me more 

 oxide of ziric from 18*1 25 of sulphate than 5*245 grains of oxide 

 of zinc. But this quantity I can always get when I take the 

 requisite pains. 



5. I have detailed rather minutely my mode of determining 

 the water and oxide in sulphate of zinc ; but it will not be 

 necessary to describe with equal minuteness the method fol-* 



}f€iu SerieSf vol. x. 2 b 



