LECTURE IV.] HISTORY OF CHEMISTRY. 65 



quantities of two bases equivalent which are neutralised by the 

 same quantity of acid, and those quantities of metal equivalent 

 which mutually precipitate each other (and therefore unite with 

 the same weight of oxygen), but that also, in his determinations, 

 he extends far beyond these limits, without, it would appear, 

 ever clearly perceiving that he falls into exactly the same error 

 that he points out to Dalton. I go further, even, and assert 

 that the uncertainty was increased by him, since he first 

 employed the equivalent in the sense of the atom, and thereby 

 attached to it the vague signification which remained connected 

 with it ; and so it was this very paper which principally led 

 chemists to the fusion of the two conceptions, and thereby to 

 the tacit and inaccurate assumption that the atoms were 

 equivalent, an error which gave rise to great confusion. 



I shall here give an example of Wollaston's determinations, 

 so that the reader may obtain at least an idea of his method, 

 and may satisfy himself as to the accuracy of my opinion. 

 Wollaston sets out from the equivalent of oxygen, which he 

 assumes = 10; from this he determines the equivalent of 

 hydrogen to be 1.3, clearly because 1.3 parts of hydrogen 

 (according to the estimations of the period) unite with 10 parts 

 of oxygen to form water; thus equivalent quantities are, with 

 Wollaston, the quantities in which substances combine. But 

 how, we may ask, does he proceed in the cases of substances 

 that combine in more than one proportion in the case of 

 carbon, for example? Does he recognise several equivalents^ 

 here ? The answer is, no, he never appears to think that such 

 a thing can be possible. He adopts the equivalent of carbon 

 as 7.5, determining it from that of carbonic anhydride, which, 

 according to him, is 27.5. He does not give any reason, 

 however, for choosing the latter number, and we are left to 

 find it out for ourselves. We might suppose that Wollaston 

 regarded as the equivalent that quantity of carbonic acid which 

 saturates a quantity of a base containing 10 parts of oxygen, 

 whereby he would necessarily have adhered to the view stated 

 above, that the combining weight is identical with the equiva- 

 lent. He is obliged, however, as a consequence from his own 



E 



