Dr. Turner on the Composition of Chloride of Barium. 181 



mistry, lead to the detection of errors that had escaped notice, 

 and which vitiate many analyses previously regarded without 

 suspicion. An instance of this kind I shall have occasion to 

 notice in the present communication. 



The foregoing reflections have been more immediately eli- 

 cited by circumstances connected with Dr. Thomson's "First 

 Principles of Chemistry." The celebrated author of that work 

 has attempted to ascertain the equivalents of all elementary 

 substances; and as the result of his labours, has inferred the 

 truth of an ingenious conjecture, suggested some years ago by 

 Dr. Prout, that the weights of the atoms of bodies are simple 

 multiples of the atomic weight of hydrogen. (Annals of Phi- 

 losophy, vol. vi. p. 321.) This hypothesis is of so much im- 

 portance if true, and may give rise to so much error if false, 

 that its accuracy cannot too soon be put to the test of a minute 

 experimental inquiry. The only chemists who to my know- 

 ledge have objected on experimental grounds to Dr. Thom- 

 son's support of this hypothesis, are Dr. Ure and Berzelius; 

 but unfortunately both these gentlemen have written on the 

 subject with such acrimony, and assumed a tone so unusual in 

 scientific controversy, as in a great degree to have destroyed 

 that confidence which their well-founded reputation for saga- 

 city and skill would otherwise inspire. The uncertainty in 

 which this question is still involved, has induced me to inves- 

 tigate it; and the essay which the Royal Society do me the 

 honour to hear this evening, may be viewed as the commence- 

 ment of a series of essays designed for the elucidation of the 

 same subject. As I shall have occasion on individual points 

 to differ repeatedly from Dr. Thomson, I embrace this oppor- 

 tunity to declare, that in considering his statements with the 

 freedom required for eliciting truth, I bear towards him no 

 other personal feelings than those of kindness for civility re- 

 ceived at his hands, and of respect for a man who has devoted 

 his life zealously and successfully to the promotion of science. 

 The object of the present essay is to determine the compo- 

 sition of chloride of barium. The frequent employment of 

 this compound in chemical experiments renders an exact 

 knowledge of its constitution peculiarly important; and it has 

 been used so extensively by Dr. Thomson as a medium of ana- 

 lysis, that an examination of it will afford an excellent criterion 

 of the accuracy of his researches. Dr. Thomson has employed 

 chloride of barium in ascertaining the equivalent of sulphuric 

 acid, and of not less than thirteen metals and their protoxides ; 

 so that if his examination of this substance is inexact, the error 

 will probably affect a large portion of his treatise. Dr. Thom- 

 son has been led by his observations to adopt 36 as the equi- 

 valent 



