on the Origin of the Doctrine of Definite Proportions, &c. 407 
a foreigner should do me that justice which my fellow-subjects of 
Scotland so shamefully withhold. 
Much of what Dr. Murray advances in his chapter on Chemi- 
cal Affinities, but particularly what relates to the various modi- 
fications occasioned by the beautiful laws of definite proportions, 
is to be found jor the first time in my Comparative View, with 
the proportions also in which the gases unite in volumes. 
The modifications of attraction occasioned by the solvent 
power of water on saline substances, gums, sugars, &c. together 
with the power by which water dissolves gases, and the gases 
water, were introduced for the first time in the same work, and 
represented as a species of influence intermediate between che- 
mical attraction and that of aggregation or gravitation, but nearer 
the former than the two latter*. 
1 also introduced another modification of attraction with which 
chemists were not acquainted at the time ; viz. that dry oxygen 
will not unite to dry inflammable bodies in the common tempe- 
rature of the atmosphere, not even with iron, without the me- 
diation of water, or a sufficiency of moisture; and that under 
‘these circumstances it is the oxygen of the water that unites 
to the inflaminable bodies, while the oxygen of the gas unites to 
the hydrogen of the water in its nascent state, so as to repro- 
duce water ;—this fact was proved by experiments f. 
Chemistry derived considerable advantage by calculating the 
relative forces of bodies to oxygen one and one and one and two, 
&c.: instance, we should not be able to account for the different, 
phenomena produced by the action of concentrated sulphuric 
acid, dilute sulphuric acid, and sulphurous acid on iron and zine 
and other metals, without this knowledge. It enables us to ac- 
count upon incontrovertible principles, that during the solution 
of iron in dilute sulphuric acid, the atom of acid is completely 
decomposed, that is, deprived of the whole of its oxygen, by the 
superior attraction of the metal for that principle ; the attraction 
of the particles of tron being 7, that of the particle of sulphur 
to its two particles of oxygen sbeing 54!,: therefore the force, 
and consequently the velocity with which the oxygen moves to- 
wards the iron, leave the sulphur far behind in the state of ulti- 
mate division ; and being within the influence of atoms of water, 
it instantly deprives the hydrogen of its oxygen ; and the ‘ul- 
phurous acid formed in this way as instantaneously unites to the 
metallic oxide so as to constitute sulphate of iron. 
When sulphurous acid is poured on iron no decomposition of 
water can take place, because the particle of sulphur being only 
* Comparative View, pages 73, 74. + Ib. page 13, or Atomic 
Theory, pages 52, 53, 
Cce4 ‘ united 
