374 -^^^ Cavendish's 'Experiments on Air, 



thruftiijg down the tube ED a wooden cylinder of fuch a lize 

 as almoil; to fill up the whole bore, and by occailonally pouring 

 quickfilv-cr into the lame tube, to fupply the place of that 

 'puthed into the ball C. After the experiment was finiflied, the 

 apparatus was weighed again, wliich Ihewed exadly how much 

 air had been forced into the tube M during the whole experi- 

 ment ; it being equal in bulk to a quantity of quicklilver, whofe 

 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, w^as 

 in general from 1 1 to | of an inch. 



It is fcarcely ncceliary to inform any one ufed to e'le6lrlcal 

 experiments, that in order to force an electrical fpark through 

 the tube, it was neceilary, not to make a communication be- 

 tw^een the tube and the conductor, but to place an infulated ball 

 at fuch a diftance from the condudor 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 quicklilver in the 

 other glafs communicated with the ground, 



I now proceed to the experiments. 



When the ele£tric fpark was made to pafs through common 

 air, included between fliort 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 leafh 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 phlogiftication, as that is very little more than one- 

 fifth of the whole. The 



