128 All Address to Chemists. [fiiu. 



Chemical proportions begin to be more generally studied ; but 

 chemists are not agreed about the laws which regulate them. One 

 party waits the opinion of those whom they consider as authorities ; 

 and these last appear to suspend their judgment, because the 

 opinion requires to be verified by experiments, tlie number and 

 difficulty of which is revolting to their minds. Let me be per- 

 mitted to point out here, what in my opinion ought to be the 

 principal object of their examination. 



Chemical proportions depend upon two cardinal points : 1. The 

 proportions in which the elementary atoms unite. 2. The propor- 

 tions in which the compound atoms combine. The first of these is 

 a necessary consequence of the atomic theory ; and as the number 

 of combinations which it includes is very limited, almost the whole 

 of them have been examined, without finding a single exception to 

 the law. Hence this point is very generally admitted. The case 

 is very different with the second point. It includes an almost in- 

 finite number of compounds, varying in their elements as to the 

 number of compound atoms which they contain. I have examined 

 a great number of these substances, and as they are for the most 

 part composed of oxides, I paid particular attention to the oxygen 

 which they contain. The laws which I considered myself as en- 

 titled to establish from tliese experiments are well known. 



The first cardinal point being established we must endeavour to 

 establish or refute the second. If the accuracy of my experiments 

 be admitted, I think their number is such that the second point 

 also may be considered as verified. If this accuracy be not ad- 

 mitted, it is obviously necessary to repeat my experiments, and 

 produce other analogous ones. My experiments have informed me 

 how very difficult and even painful this kind of labour is ; but it is 

 absolutely necessary. 1 know of only two chemists who have 

 hhherto occupied themselves with this examination, namely, 

 Mr. Vogel, of Bayreuth ; and Dr. Thomson, of London. The 

 first undertook the analysis of a set of double salts, mostly con- 

 taining vvater of crystallization ; that is to say, composed of three 

 or four oxides. The results which he obtained corresponded witli 

 the law. Dr. Thomson has in a theoretic dissertation gone over a 

 great number of saline combinations. He inclines to admit the 

 law. 



This law is of much more importance than may be supposed at 

 first. It deserves therefore the most careful and impartial exami- 

 nation. Were it not for this law, no combination composed of 

 several oxides could be calculated, nor any analysis verified in a 

 decisive manner for the theory. For it is clear, that if there be 

 combinations expressible, for example, by 2 A O' + 4 B O'^ 

 + 7CO +5HO;orif nature were to allow us to change 

 the numbers in the formulas in any manner whatever, in sucli a case, 

 all idea of determinate proportions would disappear, in proportion 

 as these combinations became more complicated. 



It is likewise by means of the law concerning the combination 



