292 Dl(: Tl/liNER ON CHLORIDE OF BARIUM. 



Stances 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 Philosophy, vol. vi. p. 321.) This hypothesis is of so 

 much importance 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 knowledge have objected on experimental 

 grounds to Dr. Thomson's support of this hypothesis, are Dr. Ure and Ber- 

 zELius ; 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 sagacity and skill would otherwise inspire. The uncertainty in 

 which this question is still involved, has induced me to investigate it ; and the 

 essay which the Royal Society do me the honour to hear this evening, may be 

 viewed as the commencement 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 opportunity 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 

 received 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 composition of chloride 

 of barium. The frequent employment of this compound in chemical experi- 

 ments renders an exact knowledge of its constitution peculiarly important ; 

 and it has been used so extensively by Dr. Thomson as a medium of analysis, 

 that an examination of it will afford an excellent criterion of the accuracy of 

 his researches. Dr. Thomson has employed chloride of barium in ascer- 

 taining 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. Thomson 

 has been led by his observations to adopt 36 as the equivalent of chlorine, 

 70 as that of barium, and 78 as that of baryta. The equivalent of chloride 



