2 7 ° Messrs. Allen and Pepys on the 
We soon found that oxygene gas, even when secured in 
bottles with ground glass stoppers, was not always to be de- 
pended upon, but was sensibly deteriorated by keeping; and 
therefore in all our experiments we made the gas within an 
hour or two of the time of using it, and always from the hy- 
peroxygenised muriate of potash. Its degree of purity was 
constantly ascertained by the eudiometer before every experi- 
ment, and was generally determined in about 10 minutes. The 
solution employed was that recommended by Professor Davy ; 
namely, the solution of green sulphate of iron saturated with 
nitrous gas ;* and whenever the diminution had arrived at 
its maximum, and the gas began to increase in volume, we 
substituted a simple solution of the green sulphate of iron 
for that saturated with nitrous gas, and always had the most 
satisfactory results ; for the simple sulphate absorbs any 
nitrous gas which may have escaped from the saturated solu- 
tion, and the residuum in this case enables us to ascertain ex- 
actly the quantity of oxygene contained in the gas. 
We determined to make our first experiment with charcoal, 
and as Morozzo and Rouppe had ascertained the absorbing 
properties of this substance, and as our results must obviously 
be influenced by it, our attention was directed to this point, the 
following quantities of different kinds of wood, sawed into slips 
J T of an inch were weighed. 
White Fir, 300 grains. 
Lignum Vitas, 800 
Box - - 400 
Beech - - 500 
English Oak, 250 
Mahogany - 200 
* This solution absorbs oxygene much more rapidly in warm weather than in cold. 
