1825.] Method of analyzing Sulphate of Zinc, 367' 



analyses added together gave me the quantity of oxide of zinc 

 in 181*25 grains (10 atoms) of sulphate of zinc. It will be 

 sufficient if I state here one of these two analyses. j. 



(2.) The salt was weighed in a small flask ; distilled watetr! 

 was poured into it, and it was placed on the sand bath till the 

 salt was dissolved. 90 grains (five atoms) of crystalHzed car- 

 bonate of soda, previously reduced to coarse powder, were 

 then put into the flask, and the flask was gently agitated till 

 the whole of this last salt had dissolved. This process was 

 usually over in about 10 minutes, and the temperature of the 

 liquid was about 70^. As the carbonate of soda dissolved^ 

 carbonate of zinc was deposited in white flocks ; this carbonate 

 was immediately collected by pouring the whole contents of 

 the flask upon a double filter. The carbonate of zinc was 

 washed with distilled water till the liquid that passed through 

 the filter ceased to produce any effect on muriate of barytes. 

 The object of this part of the experiment was to ascertain how 

 much carbonate of zinc would be precipitated from a cold 

 solution of five atoms of sulphate of zinc by five atoms of <iai«'> 

 bonate of soda. 



The carbonate of zinc thus obtained was dried upon the filter 

 in a temperature, which never much exceeded 212°. It was then 

 weighed by placing the balanced filters in the two opposite 

 scales of the balance ; the weight in different experiments 

 varied from 29*3 to 31*03 grains; as much of this carbonate as 

 possible was detached from the filter, and after being weighed 

 in a balanced platinum crucible of a very small size, was heated 

 to redness in the flame of a spirit lamp. From the loss of 

 weight sustained by the portion thus treated, it was easy to 

 infer how much the whole carbonate would have lost; there 

 remained 20*37 grains of oxide of zinc. There was scarcely 

 any difference in the amount of this weight in different experi- 

 ments, provided sufficient care had been taken not to vary the 

 previous steps of the process. 



(3.) The liquid which had passed through the filter together 

 with all the washings (properly concentrated) was put back 

 into the flask. It had the property of rendering cudbear paper 

 purple ; but after being boiled for about half an hour it was 

 capable of reddening vegetable blues. It was obvious from 

 this, that the whole of the soda had not united with the sul- 

 phuric acid of the sulphate of zinc ; but that this union was 

 effected by half an hour's boiling. During the boiling, an 

 additional precipitate fell, not in loose white flocks as th6 first 

 precipitate, but in a powder which was less white and much 

 heavier; for it fell much more rapidly to the bottom. The 

 liquid thus treated was thrown upon a double filter, and the 

 powder (6) remaining on the filter, was washed with distilled* 

 water till the liquid ceased to affect muriate of barytes. ' 



