154 Dr. Pearson’s Experiments and Observations 
times during the process, that combustion had been excited 
several times before ; not only in the present experiment, but 
perhaps in the former ones, without observing it I con- 
ceived that a gradual combustion also, very probably, took 
place in this process, by the kindling of bubbles of gaz in their 
ascent through the water. I now perceived that the discharges 
ought to be produced more slowly, or the tubes to be wider, to 
allow the bubbles to pass quite through the water, in order to 
avoid the accension of gaz during the process. My calculation 
also, that 35 to 40000 discharges were requisite to produce one 
cubical inch of gaz from water, containing its usual quantity 
of common air, was rendered much more vague by this accen- 
sion, so often liable to be occasioned. 
To the gaz which remained in the tube in this experiment 
was added an equal bulk of nitrous gaz; the mixture dimi- 
nished to 1,5; and on adding to the residue half its bulk of 
oxygen gaz, and passing through it the electrical spark, no 
accension or diminution of bulk was produced. Hence all the 
hydrogen gaz and oxygen gaz, produced by the decomposition 
of the water, had been burnt during the process ; the oxj'gen 
gaz thus detected being considered to be only that expelled 
from the water. 
Experiment iv. By means of electrical discharges, with 
the apparatus used in the preceding experiment, I obtained 
gaz from New River water ; letting it up into a reservoir as 
soon as about ^ of a cubic inch was produced, till I had 
collected { of a cubic inch. To this was added an equal 
bulk of nitrous gaz; on which the mixture diminished to 1,2 ; 
and on the addition of a little more nitrous gaz, no further di- 
minution took place. To this residue half its bulk of oxygen 
