VOL. LXXVIII.] PHILOSOPHICAL TKANSACTIONS. 455 



remaining in the tube, when Mr. Gilpin left off working, was 600 measures; 

 but at the time the produce was examined, it was reduced to about 120, so much 

 having been absorbed without the help of any electrification, which is a still more 

 remarkable instance of spontaneous absorption than what occurred in the former 

 experiment. A few days after the experiment began, a black film was formed in 

 one of the legs, which I suppose must have been a mercurial ethiops; but whe- 

 ther owing to some small degree of foulness in the mercury or tube, or to any 

 other cause, I cannot tell. This foulness seemed not to increase; but on March 

 10, when the air absorbed was about 3200, a whitish sediment began to appear 

 on the surface of the mercury. - 



On March IQ, the produce was examined in the presence of Dr. Blagden, Dr. 

 Dollfuss, Dr. Fordyce, Dr. Heberden, Dr. J. Hunter, Mr. Macie, and Dr. 

 Watson. The mixed air forced into the bent tube from the reservoir was 6650 

 measures, besides which Mr. Gilpin had at different times introduced 630 of 

 common air, which makes in all 7280, containing 4570 of dephlogisticated, and 

 2710 of common air. The soap-lees were evaporated to dryness as before. The 

 residuum weighed 2 gr., but there were 2 or 3 globules of mercury mixed with it, 

 which might very likely weigh -f gr. This being dissolved in a small quantity of 

 water, the following experiments vi'ere made with it. It did not at all discolour 

 paper tinged with blue flowers. Slips of paper were dipped into it, and dried; 

 and, by way of comparison, other slips of paper were dipped into a solution both 

 of common nitre and phlogisticated nitre, and also dried. The former burnt in 

 the same manner, and with as strong marks of deflagration, as the latter. It 

 had a strong taste of nitre, but left also a slight metallic taste on the tongue. It 

 did not give any white colour to a piece of clean copper put into it. 



In order to see whether the whitish sediment, which was before said to be 

 formed in the bent tube, contained any mercury, the remainder of this solution 

 was diluted with some more distilled water, and suffered to stand till the white 

 sediment had subsided. The clear liquor being then poured off, the remainder, 

 containing the sediment, which seemed to amount only to a very small quantity, 

 was put on a piece of bright copper, and dried on it; a piece of clean gold was 

 then laid over it, and both were exposed to heat. Both metals acquired a whitish 

 colour, especially the gold, but which was very indeterminate. In order to dis- 

 cover how nice a test of alcalinity the paper tinged with blue flowers was, a satu- 

 rated solution of common nitre was mixed with -^-^ of its bulk of the soap-lees; 

 and this mixture was found to turn the paper evidently green; so that, as the so- 

 lution of nitre contains about twice as much alkali as the soap-lees, it appears, 

 that if the residuum had wanted only -^^s- part of being saturated, it would have 

 discoloured the paper. 



From the foregoing trials it appears, that the mixture of dephlogisticated and 



