452 PHILOSOPHICAL TRANSACTIONS. [aNNO I788. 



were prepared from salt of tartar, and were of such strength as to yield -^ of 

 their weight of nitre when saturated with nitrous acid. The dephlogisticated air 

 was prepared from turbith mineral, and seemed by the nitrous test to contain 

 about -yV part of phlogisticated air. 



On Dec. 6, 1787, in the presence of Sir Joseph Banks, Dr. Blagden, Dr. 

 Dollfuss, Dr. Fordyce, Dr. J. Hunter, and Mr. Macie, the materials were put 

 together. The quantity of soap-lees, introduced into the bent tube, was 180 

 measures, each of which contained 1 gr. of quicksilver; and, as the bore of the 

 tube was rather more than -f of an inch in diameter, it formed a column of 5 or 

 6 tenths of an inch in length, which, by the introduction of the air, was divided 

 into 2 parts, one resting on the quicksilver in one leg of the tube, and the other . 

 on that in the other leg. The dephlogisticated air was mixed with ^ part of its 

 bulk of atmospheric air of the room in a separate jar, and the reservoir was filled 

 with the mixture; and from it Mr. Gilpin, as occasion required, forced air into 

 the bent tube, to supply the place of that absorbed by means of the electric 

 spark. Hence it appears, that the mixture employed contained a less proportion 

 of common air than that used in either of my experiments. This made it neces- 

 sary for Mr. Gilpin now and then to introduce some common air by means of the 

 bent tube, whenever from the slowness of the absorption he thought there was 

 too small a proportion of phlogisticated air in the tube. My reason for this 

 manner of proceeding was, that as my first experiment seemed to show, that the 

 dephlogisticated air ought to be in a rather greater proportion to the phlogisticated 

 than the latter did, I was somewhat uncertain as to the proper quantities, and 

 doubted whether I could proportion them in such manner as that it should not 

 be necessary, during the course of the experiment, to add either dephlogisticated 

 or common air. I therefore mixed the airs in such proportion, that I was sure 

 there could be no occasion to add the former; since it was much easier, as well 

 as more unexceptionable, to add common air than dephlogisticated. 



On Dec. 24, as the air in the reservoir was almost all used, this apparatus was 

 again filled in the presence of most of the above-mentioned gentlemen, with a 

 mixture of the same dephlogisticated air and common air, in the same propor- 

 tions as before; and the same thing was repeated on Jan. IQ. On Jan. 23, the 

 bent tube was, by accident, raised out of one of the glasses of mercury into which 

 it was inverted, by which it was filled with air, and a good deal of the soap-lees 

 were lost; there was enough however remaining for examination. 



On Jan. 28, and 29, the produce of this experiment was examined in the pre- 

 sence of Sir Joseph Banks, Dr. Blagden, Dr. Dollfuss, Dr. Fordyce, Dr. He- 

 berden, Dr. J. Hunter, Mr. Macie, and Dr. Watson. It appeared that 9290 

 measures of the mixed air had been forced into the bent tube from the reservoir.* 



* The method of ascertaining the quantity of air forced in was by weighing the reservoir, as men- 

 tioned in the above-mentioned paper, p. 374. — Orig. 



