On Chemical Equivalents. 103 



called an atom and an half to an atom. Yet the Daltonian 

 commentator, on the second occasion, counts one volume an 

 atom of hydrogen, and on the first, two volumes an atom. 



We should steer clear of all these gratuitous assumptions and 

 contradictions, by making a single volume of hydrogen represent 

 its atom, or prime equivalent. " There is an advantage," «avs 

 Dr. Prout, " in considering the volume of hydrogen equal to tiie 

 atom, as in this case, the specific gravities of most, or perhaps 

 all elementary substances (hydrogen being one) will either ex- 

 actly coincide witls, or be some multiple of, the weights of their 

 atoms ; whereas, if we make the volume of oxygen unity, the 

 weiglits of the atoms of most elementary substances, except oxy- 

 gen, will be douI)le that of their specific gravities, with respect 

 to hydrogen. The assumption of the volume of hy-drogen be- 

 ing equal to the atom, will also enable us to find more readily, 

 the specific gravities of bodies in their gaseous state, (either with 

 respect to hvdrogeji, or atmospheric air,) by means of Dr. Woi- 

 lastoti's logomctric scale. 



'^ If the views we have ventured to advance be correct, we mav 

 almost consider the tt^wt*] l»'a^ of the anc-ieiits to be realized in 

 hydrogen; an opinion, by the by, not altogether new. If wc 

 actually consider this to be the case, and fuither consider the 

 specific gravities of bodies, in their gaseous state, to represent 

 the number of volumes condensed into one; or in other words, 

 the number of the absolute weight of a single volume of the first 

 matter (TroMrrj uXrj) which they co'itain, which is extremely pro- 

 bable ; multiples in weight must always indicate nniltiples in 

 volume, and vice versa ; and the specific gravities or absolute 

 weights of all bodies in a gaseous state, must be multiples of the 

 specific gravity, or absolute weight of the first matter, (-Trgwrr, 

 5x>i), because all bodies in a gaseous state, which unite with one 

 aiiHtlser, unite with reference to their volume." 



From these ingenious oliservations, we i)erceive the singular 

 felicity of juduement, with which vSir H. Davy made choice of 

 the single volume of hydrogen, for the unit of primary combina- 

 tion, in his Elements of Chemical Philosopliy. 



Mr. Dalton's prelections on the atomic theory, and Dr. 

 Thomson's commentary, had excited but a feeble sensation in 

 the chemical world. That part oi' his system which treated on 

 caloric, was blended with so much mere hypothesis, tl.at chemists 

 transferred a portion of the scepticism thus created, to his col- 

 lacion of primary and niultijjie combinalitins. It was Dr. VV'ol- 

 laston who first decided public opinion in favour of the doctrine 

 of multiple proportions, by his elegant paper on super-aeid and 

 sub-acid salts, iiincrtcd in the Philosuj)hical Transactions for 



I SOS. 



