1 1 8 Sir B e n j am i n Thompson ’s Experiments 
plant, inftead of being removed, were rather confirmed by the 
refill t of the experiments of which I have given an account in 
the foregoing letter ; and however difpofed I was to adopt the 
beautiful theory of the purification of the atmofphere by the 
vegetable kingdom, 1 was not whiling to admit a fa£t which 
has been brought in fupport of it, till it fhould appear to me 
to have been demon ftrated by the moft decifive experiments. 
That the frefh leaves of certain vegetables, expofed in water 
to the aflion of the fun’s rays, caufe a certain quantity of 
pure air to be produced, is a fact which has been put beyond 
all doubt ; but it does not appear t© me to be by any means fo 
clearly proved, that this air is “ elaborated in the plant by the 
“ powers of vegetation “ phlogifticated or fixed air being 
“ firft abforbed or imbibed by the plant as food, and the dephlo- 
gifticated air being rejefted as an excrement :” for, befides 
that many other fubftances, and in which no elaboration, or 
circulation, can poffibly be fufpefted to take place, caufe the 
water in which they are expofed to the aflion of light to yield 
dephlogifticated air as well as plants, and even in much greater 
quantities, and of a more eminent quality, the circumflances 
of the leaves of a vegetable, which, accuftomed to grow in air, 
are feparated from-its Item, and confined in water, are fo un- 
natural, that I cannot conceive, that they can perform the 
fame functions in fuch different fituations. 
Among many fadls which have been brought in fupport of 
the received opinion of the elaboration of the air in the veffels 
of the plants in the experiments in queftion, there is one upon 
which great ftrefs has been laid, which, I think, requires fur- 
ther examination. 
The frefh healthy leaves of vegetables, feparated from the 
plant, and expofed in water to the aflion of the fun’s rays, 
5 appear, 
