31 
fresh plant put in its place, to try if it would imbibe 
,any more of the air, but it faded in four or five days ? 
and yet a fresh plant, put into the other vessel, whose 
air had been confined for the same time, lived nearly a 
month, or almost as long as another plant lived in 
newly confined air *. 
241. This great diminution of the air of the vessel 
in which the mint had grown, Dr Hales supposed to 
afford a proof that the leaves and stems of plants im- 
bibe elastic air ; but we now know that carbonic acid 
must have been formed, and afterwards attracted by 
the water over which the vessel was inverted. That 
the pure part of the air had, in a great measure, dis- 
appeared, may be inferred, also, from its incapacity 
to support a fresh plant that was placed in it, which 
the air, confined the same time in a similar vessel, 
was found able to do. Dr Hales himself, indeed, 
proved this fact by an analysis of the residual air; for 
he found, that, after being infected by the mint, so 
that a fresh plant would not grow in it, it suffered a 
farther diminution of four cubic inches, when a mix- 
ture of sulphur and iron-filings with water was placed 
in it. If, therefore, we consider the first diminution 
of the air by the plant to have been occasioned by the 
formation and attraction of seven cubic inches of car- 
bonic acid (which is one-seventh of the whole air 
employed), and add to it four cubic inches of oxygen 
gas, abstracted by the mixture of iron and sulphur, 
we shall have eleven cubic inches as the whole loss 
which the air suffered ; and i = T .i T , we now know 
Veg. Statics, vol. i. p. 32^, 1st edit. 
