410 On the Composition of Oxide of Zinc. [Db<v. 



the general result of the comparison, are particulars which ob- 

 viously belong to the consideration of the learned in this cele- 

 brated society} and they appear highly worthy of their attention 

 and their zeal. 



Article III. 



On the Composition of Oxide of Zinc. By Thomas Thomson, 



M.D. F.R.S. 



In the table of the proportions in which chemical bodies 

 unite, published in the Annals of Philosophy , vol. ii. p. 42, I 

 have stated that the oxide of zinc is composed of 100 metal + 

 23175 oxygerf. This number is the mean of experiments made 

 to determine the point by Berzelius, Davy, and myself. But as 

 the zinc of commerce, with which my experiments, and those 

 of Sir Humphry Davy, had been made, is always contaminated 

 with some lead, and not unfrequently also with copper, it is 

 obvious that experiments to determine the composition of the 

 oxide of zinc bv directly oxidating that metal cannot be perfectly 

 accurate, and will probably give the proportion of oxygen below 

 the truth. This consideration induced me to make a set of expe- 

 riments in a different way, and susceptible of greater accuracy, 

 in order to see how far the proportions which I had stated in the 

 table deviated from the truth. I shall here give the result of my 

 experiments for the satisfaction of my readers. 



1. The sulphuric acid which I had in my possession was of the 

 specific gravity 1 -83993, at the temperature of 60°. My first 

 object was to ascertain the proportions of real acid and water 

 contained in this liquid: 100*4 grains of the acid were diluted 

 with water, neutralized by a base, and precipitated by muriate 

 of barytes. The sulphate of barytes obtained was washed, dried, 

 and exposed to a red heat. It weighed 220*1 grains. The 

 experiment being repeated, the sulphate of barytes obtained 

 weighed 223*78 grains. A third experiment was made with 

 100*06 grains of the acid. The sulphate of barytes obtained 

 weighed 220*67 grains. These experiments were all made with 

 equal care; and the want of agreement between them must be 

 ascribed to the imperfection of our methods of experimenting, 

 and not to any want of attention on my part. If we consider 

 sulphate of barytes as composed of 100 acid +194 base, ac- 

 cording to the experiments of Berzelius, then the sulphuric acid 

 is composed 



