[ 1 S I ] 
creafed in weight 40A grains. Therefore the air 
prelTed out of the bladder weighs 40 f grains lefs than an 
equal quantity of common air : but the quantity of air 
prelTed out of the bladder mud; be nearly the fame as 
that which was forced into it, i. e. 80 ounce meafures : 
confequently 80 ounce meafures of this fort of inflam- 
mable air weigh 40T grains lefs than an equal bulk of 
common air. The three other forts of inflammable air 
were then tried in the fame way, in the fame bladder, 
immediately one after the other. In the trial with the 
air from zinc by fpirit of fait, the bladder increafed 
407 grains on forcing out the air. In the trial with the 
air from iron, it increafed 414 grains, and in that with 
the air from tin, it increafed 41 grains. The heat of 
the air, when this experiment was made, was 50°; 
the barometer flood at 294 inches. 
There feems no reafon to imagine, from thefe 
experiments, that there is any difference in point of fpe- 
cific gravity between thefe four forts of inflammable 
air 5 as the fmall difference obferved in thefe trials is 
in all probability lefs than what may arife from the 
unavoidable errors of the experiment. Taking a 
medium therefore of the different trials, 80 ounce mea- 
fures of inflammable air weigh4i grains lefs than an 
equal bulk of common air.' Therefore, if the denfity 
of common air, at the time when this experiment 
was tried, was 8co times lefs than that of water, 
which, I imagine, muff be near thS truth inflam- 
'* Mr. Hawkfbee, whofe determination is ufuallv followed as 
the mod exadt, makes air to be more than 850 times lighter than 
water ; vid. Hawkfbee’s experiments, p. 94, or Cotes’s Hydro- 
ftatics, p. 159. But his method of trying the experiment muft in 
all probability make it appear lighter than it really is. for 
m able 
