[ * 5 ° ] 
could be fare of. Some more of each of the above 
parcels of air were then mixed with common air, in the 
proportion of 7 parts of inflammable air to 34 of 
common air, and tried in the fame way as before. 
They each of them went off with a gentle bounce, 
and burnt fame time in the bottle, without my being 
able to perceive any difference between them. 
In order to avoid being hurt, in cafe the bottle 
fhould burfl by the explofion, I have commonly, 
in making thefe fort of experiments, made life 
of an apparatus contrived in fuch manner, that, by 
pulling a firing, 1 drew the flame of a lamp over the 
mouth of the bottle, and at the fame time pulled off 
the cap, while I flood out of the reach of danger. I 
believe, however, that this precaution is not very necef- 
fary ; as I have never known a bottle to burff in any of 
the trials I have made. 
The fpeciflc gravity of each of the above-mentioned 
forts of inflammable air, except the faff, was tried in 
the following manner. A bladder holding about 100 
ounce meaiures was fllledwith inflammable air, in the 
manner reprefented in Fig. 3. and the air preffed out 
again as perfectly as poflible. By this means the 
Imall quantity of air remaining in the bladder was 
almoft intirely of the inflammable kind. 80 ounce 
meafares of the inflammable air, produced from zinc 
by the vitriolic acid, were then forced into the bladder 
in the fame manner : after which, the pewter pipe was 
taken out of the wooden cap of the bladder, the 
orifice of the cap flopt up with a bit of lute, and the 
bladder weighed. A hole was then made in the lute, 
the air preffed out as perfe&ly as poflible, and the 
bladder weighed again. It was found to have in- 
creafed 
