262 Mr . Cavendish’s Experiments on the 
method ufed for introducing air into the bent tube, was 
that defcribed in the laft paragraph of p. 373. in that 
Paper, by means of the apparatus reprefented in fig. 3. or 
the refervoir, as I fhall call it. The foap-lees, like thofe 
of my own experiments, were prepared from fait of tartar, 
and were of fuch ftrength as to yield ^ of their weight 
of nitre when faturated with nitrous acid. The dephlo- 
gifticated air was prepared from turbith mineral, and feemed 
by the nitrous tell to contain about T * T part of phlogiflicated 
air. v 
On December 6, 1787, in the prefence of Sir Joseph 
Banks, Dr. Blagden, Dr. Dollfuss, Dr. Fordyce, Dr. 
J. Hunter, and Mr. Macie, the materials were put toge- 
ther. The quantity of foap-lees, introduced into the bent 
tube, was 180 meafures, each of which contained one grain 
of quickfilver ; and, as the bore of the tube was rather more 
than one-third of an inch in diameter, it formed a column of 
five or fix-tenths of an inch in length, which, by the intro- 
duction of the air, was divided into two parts, one refting on 
the quickfilver in one leg of the tube, and the other on that in 
the other leg. The dephlogifticated air was mixed with one- 
third part of its bulk of atmofpheric air of the room in a fepa- 
rate jar, and the refervoir was filled with the mixture ; and 
fronv thence Mr. Gilpin, as occafion required, forced air into 
the bent tube, to fupply the place of that abforbed by means 
of the elettric fpark. 
From what has been faid, it appears, that the mixture em- 
ployed contained a lefs proportion of common air than that 
ufed in either of my experiments. This made it neceffary for 
Mr. Gilpin now and then to introduce fome common air by 
4 means 
