PREFACE. XV11 



and consequently, that 17 grains of sulphate of zinc do 

 not contain so much as 5 grains of sulphuric acid. 



I have been in the habit, ever since the atomic numbers 

 given in the present work were determined, to calculate 

 the experiments of other chemists by substituting for the 

 data which they employed, the more correct data which I 

 myself possessed, and I have frequently found that the 

 experiments, when so calculated, came much nearer the 

 truth than the experimenters themselves were aware of. 

 This was remarkably the case with respect to Mr. Fara- 

 day's experiments to determine the constituents of the 

 chlorides of carbon, for a knowledge of which we are 

 indebted to that very ingenious and accurate chemist. 

 The imperfect data which he employed has given his 

 experiments the appearance of greater inaccuracy than 

 the truth : for when the specific gravities and atomic 

 numbers given in the following pages are substituted for 

 those which he used, his experiments almost coincide 

 with the theoretic quantities. 



In this country, the atomic weights which I here pre- 

 sent to the public, have been already very generally 

 adopted, so far as they are known. But on the continent, 

 the numbers and tables of Berzelius are in common use. 

 Berzelius' numbers are in general very near approxima- 

 tions to the truth ; though I am persuaded that in very 

 few instances he has actually reached it. His tables 



VOL. I. b 



