in Derwent Lake, Kesnick. 69 
[ Note, by Mr. Dalton}. Being at Keswick in 1816, Mr. 
Otley and I procured an apparatus for collecting a quantity 
of the inflammable gas generated in the floating island, then 
sunk two or three feet below the surface of the lake. We an- 
chored a boat over the island, and with a long piked staff 
penetrated to the depth of a foot or more below the surface 
of the island. Each time the pike was withdrawn, a gush 
of air ascended in large bubbles, to the amount of a pint, 
more or less; part of which we caught by a bottle and fun- 
nel, without suffering it to come in contact with the atmo- 
sphere. This gas I found afterwards to consist of equal parts 
carburetted hydrogen and azotic gasses with about 6 per 
cent. of carbonicacid. The carburetted hydrogen was such 
that 1 part required 2 of oxygen for its complete combustion 
by. electricity. It seems most probable that this gas is ge- 
nerated by the decomposition of vegetable matter in con- 
tact with water; two atoms of carbone decompose two of 
water and form at the same instant an atom of carburetted 
hydrogen and one of carbonic acid. The carbonic acid, be- 
ing absorbable by water, is mostly dispersed, and the other 
gas collects in small bubbles in the spongy texture of the 
soil till it is disturbed, when the bubbles unite and ascend 
inabody. The azotic gasis probably from the atmosphere 
by means of the water. The almost total absence of oxy- 
gen gas from such mixtures is remarkable. 
Mr. Otley has, I apprehend, suggested the only plausible 
cause that can be assigned for the rising and sinking of the 
island. The generation and temporary adhesion of such 
immense quantities of elastic fluid, must have great influence 
upon the sp. gr. of any mass; and when the mass happens 
to be nearly of the same sp, gr. as water and immersed in it, 
it will sink or swim according as the adhering volume of air 
is less or more, just as a cork loaded with lead floating i in 
water does, in the common experiment in pneumatics. 
