56 OXYGEN AND HYDROGEN GASES. 



grains of the neutral sulphate of zinc 

 were dissolved in distilled water, and precipitated 

 by a solution of carbonate of soda. The pre- 

 cipitate was separated from the liquid by means 

 of a double filter, consisting of two pieces of 

 unsized and well washed printing paper, made 

 previously of the same weight. The carbonate 

 of zinc on the filter was washed with distilled 

 water, till the liquid which passed through 

 ceased to render muriate of barytes muddy. 

 The filter was suspended in a linen bag above 

 the sand bath, in a temperature of 85, till 

 it was apparently dry ; and it was finally 

 left for some time in a temperature of about 

 ^12. It was afterwards weighed by placing 

 the two filters in opposite scales, and adding 

 weights till the two scales were exactly coun- 

 terpoised. The weight of the carbonate of zinc 

 was exactly 8 grains. It was put into a pla- 

 tinum crucible, which was covered with a lid, 

 and exposed for half an hour to a red heat, 

 There now remained 5*%5 grains of oxide of 

 zinc. 



Thus it appears, that 18*125 grains of sul- 

 phate of zinc, in crystals, contain 5*25 grains 

 of oxide of zinc. It is still easier to prove that 

 the sulphuric acid contained in this quantity of 

 the salt weighs precisely 5 grains. 



But it will be necessary to state, in the first 

 place, that when 15-5 grains of crystallized 



