VOL. LXXVIII.] PHILOSOPHICAL TRANSACTIONS. 457 



experiment the bulk of the phlogisticated air was 12-rV that of the soap-lees. In 

 my first experiment^it was 1 1-fV, and in my last 10-i\- 



As many persons seem to have supposed that the diminution of the air in 

 these experiments is much quicker than it really is, though I do not know any 

 thing in my paper which should lead to suppose that it was not very slow, it may 

 be proper to say something on this head. As the quickness of the diminution 

 depends so much on the power of the electrical machine, I can only speak as to 

 what happens with the machine used in these experiments. This was one of 

 Mr. Nairne's patent machines, the cylinder of which is 124- inches long, and 7 

 in diameter. A conductor of 5 feet long, and 6 inches in diameter, was adapted 

 to it, and the ball which received the spark was placed at 2 or 3 inches from 

 another ball, fixed to the end of the conductor. Now, when the machine 

 worked well, Mr. Gilpin supposes he got about 2 or 300 sparks a minute, and 

 the diminution of the air during the half hour which he continued working at a 

 time, varied in general from 40 to 1 20 measures, but was usually greatest when 

 there was most air in the tube, provided the quantity was not so great as to pre- 

 vent the spark from passing readily. 



The only persons I know of, who have endeavoured to repeat this experiment, 

 are, M. Van Marum, assisted by M. Pacts Van Trootswyk; M. Lavoisier, in 

 conjunction with M. Hassenfratz; and M. Monge. I am not acquainted with 

 the method which the 3 latter gentlemen employed, and am at a loss to conceive 

 what could prevent such able philosophers from succeeding, except want of 

 patience. But M. Van Marum, in his Premiere Continuation des Experiences, 

 faites par le moyen de la Machine electrique Teylerienne, p. 182, has described 

 the method employed by him and M. Van Trootswyk. They used a glass tube, 

 the upper end of which was stopped by cork, through •which an iron wire was 

 passed, and secured by cement, and the lower end was immersed into mercury; 

 so that the electric spark passed from the iron wire to the soap-lees. After so 

 much of a mixture of 5 parts of dephlogisticated and 3 of common air as was 

 equal to 21 times the bulk of the soap-lees* was absorbed, some paper was 

 moistened with the alkali, which by its burning appeared to contain nitre, but 

 showed that the alkali was not near saturated. The experiment was then conti- 

 nued with the same soap-lees till more of the air, equal to 06 times the bulk of 

 the soap-lees, was absorbed, which is near double the quantity required to satu- 

 rate them ; but yet the diminution went on as fast as ever. It was then tried, by 

 the burning of paper dipped into them, how nearly they were saturated; but they 

 still seemed far from being so. 



The circumstance of using the iron wire appears evidently objectionable, on 

 account of the danger of the iron wire being calcined. by the electric spark, and 



• This is rather more than half of that requisite to saturate the soap-lees.— Orig. 

 VOL. XVI. / 3 N 



