DR. TURNER ON CHLORIDE OF BARIUM. 
292 
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 
hear 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 30 as the equivalent of chlorine, 
70 as that of barium, and /8 as that of baryta. The equivalent of chloride 
