52 SfXTH REPORT — 1836. 



The author assigns reasons for adopting 16 as the atomic weight of 

 oxj'gen, when that of hydrogen is taken = 1. 



It is seen that the calculated specific gravity exceeds that found by 

 experiment in three of the ten compounds even when carbon is 12 ; in 

 all cases there is an excess when 12:^ is used; and except in naphthaline 

 the defect is always much less than the excess, which gives the prefer- 

 ence to 12 for the atomic weight of carbon. 



The author next proceeds to deduce from the theory important facts 

 which are already known to chemists as ultimate results of their expe- 

 riments. These are embodied in eight propositions with corollaries, of 

 which the last is here given. 



Prop. 8. Taking each elementary atom as representative of a volume, 

 then in all strictly chemical combinations, that is, whenever there is a 

 condensation, the resulting volume is always, without exception, either 

 one or two volumes exactly. Since after combination the volume is 

 diminished, the centre of some atom, or those of several atoms, have 

 penetrated the atmospherule of some other (prop. 3 and cors.) 



1 . When the atmospherule of one atom or single group is penetrated 

 by the centres of all the others, the result is a single group, (def. 1 .) and 

 consequently (prop. 3, cor. 1) the result will be one volume exactly. 



2. When the atmospherule is not penetrated by all the centres of 

 the others, then one or more of the atoms will be brought by their mu- 

 tual actions to the interval between the two remaining atoms, or single 

 groups, which combine, and thus situated, will (prop. 3, cor. 3) supply 

 the effect of the aethereal matter, which it displaces ; hence the whole 

 will form a double group, and (same cor.) will become two volumes 

 exactly. 



3. When one atom or single group combines with a double group, 

 the centres of the combining atoms will penetrate the atmospherule of 

 the double group, otherwise there would be only cohesive combination ; 

 hence the compound will continue a double group, and form two volumes 

 (prop. 3, cor. 3), except when the mutual actions bring all tlie centres 

 within the sphere of repulsion of one of them, thus constituting one 

 volume (prop. 3, cor. 1). Hence still we shall have either a single or 

 double group, and it is, from this, evident that no other case can occur ; 

 therefore the resulting volume will be always exactly one or two, how- 

 ever many volumes combine. 



Cor. This prop, embraces, simplifies, and extends the theory of 

 volumes. 



Having deduced this remarkable law from theoiy, it became import- 

 ant to know if such an unexpected result be true in fact or not. To 

 determine this point Mr. Exlej'' carefully examined all the compound 

 gases and vapours, whose specific gravities had been obtained by expe- 

 riment, as far as he could find them in the best authors. These, to the 

 amount of fifty-seven, are inserted in the following table. The specific 

 gi-avities are calculated according to this law, from the atomic weights 

 as given by Dr. Thompson, doubling some of his numbers to correspond 

 with oxygen 16, and in every instance they agree within the allowable 

 liuaits of unavoidable errors in experiments of that kind, except in boro- 



