374 Afr. Cavendish’s Experiments on Air. 
thruftiiig down the tube ED a wooden cylinder of fuch a fiz! ( 
as almoft to fill up the whole bore, and by occafionally pouring 
quickfilver into the fame tube, to fupply the place of that 
puflied into the ball C. After the experiment was finilhed, the 
apparatus was weighed again, which (hewed exactly how much 
air had been forced into the tube M during the. whole expen 
fnent ; it being equal in bulk to a quantity of quickfilver, whofi 
weight was equal to the increafe of weight of the apparatus. 
The bore of the tube M ufed in molt of the following ex- 
periments, was about one-tenth of an inch ; and the length of 
the column of air, occupying the upper part of the tube, was 
in general from i| to f of an inch. 
It is fcarcely neceflary to inform any one ufed to electrical 
experiments, that in order to force an electrical fpark through 
the tube, it was neceflary, not to make a communication be- 
tween the tube and the conductor, but to place an infulated ball 
at fuch a diftance from the conductor as to receive a fpark from 
it, and to make a communication between that ball and the 
quickfilver in one of the glafles, while the quickfilver in the 
other glafs communicated with the ground. 
I mow proceed to the experiments. 
When the eleCtric fpark was made to pafs through common 
air, included between (hort columns of a folution of litmus, 
the folution acquired a red colour, and the air was diminifhed, 
conformably to what was obferved by Dr. Priestley. 
When lime-water was ufed inftead of the folution of litmus, 
and the fpark was continued till the air could be no further di- 
minifhed, not the leafl: cloud could be perceived in the lime- 
water; but the air was reduced to two- thirds of its original 
bulk ; which is a greater diminution than it could have fuffered 
by mere phlogiflication, as that is very little more than one- 
fifth of the whole. The 
