relating to Air and Water , 29 y 
air, and alfo the addition of weight gained by the iron, are 
much more eafily afcertained in thefe experiments than the 
quantity of water expended in them, on account of the great 
length of the veffels 11 fed in the procefs, and the different quan- 
tities that may perhaps be retained in the worm of the tub, 
though I did not fail to ufe all the precautions that I could think 
of to guard againft any variation on thefe accounts. 
Of the many experiments which I made with iron y I fhall 
content myfelf with reciting the following refults. With the 
addition of 267 grains to a quantity of iron, and the lofs of 
33 6 grains of water, I procured 840 ounce meafures of in- 
flammable air ; and with the addition of 140 grains to another 
quantity of iron, and the confumption of 253 grains of water, 
I got 420 ounce meafures of air *. 
The inflammable air produced in this manner is of the 
lighted: kind, and free from that very ojf'enfive fmell which is 
generally occafioned by the rapid folution of metals in oil of 
vitriol, and it is extricated in as little time in this way as it is 
poffible to do it by any mode of folution. On this account it 
occurred to me, that it muft be by much the cheapefl method 
that has yet been ufed of filling balloons with the lighted: inflam- 
mable air. For this purpofe it will be proper to make ufe of 
caft-iron cylinders of a confiderable length, and about three or 
four inches, or perhaps more, in diameter. Though the iron 
tube itfelf will contribute to the production of air, and there- 
fore may become unfit for the purpofe in time ; yet, for any 
* If the perfect accuracy of the former of thefe experiments may be depended 
on (and it may always be prefumed, that thofe in which little water is expended 
are preferable to thofe in which more is confumed) the water that neceflarily enters 
into this kind of inflammable air is about equal in weight to the phlogffton that is 
in it. But I propofe to give more particular attention to this fubjeri:. 
Vol. LXXV. 
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