454 PHILOSOPHICAL TRANSACTIONS. [anNO 1788. 



absorbed at that time was only 4830 measures, which is much less than what 

 seems requisite to saturate the alkali, and as the diminution immediately went on 

 again on adding more common air, it seems not likely that the soap-lees were 

 saturated at that time. 



On Jan. 10, Mr. Gilpin observed a small quantity of whitish sediment on the 

 surface of the mercury; which seems to show that the soap-lees were then satu- 

 rated, and that the acid was beginning to corrode the mercury. The quantity of 

 air absorbed was also 6840 measures, which is about as much as I expected would 

 be required. However, as I was persuaded, from the event of my own experi- 

 ments, that the diminution would either entirely cease', or go on very slowly, as 

 soon as the soap-lees were saturated; and as I was unwilling to stop the experi- 

 ments before that happened, I thought it best to continue the electrification. 

 On the same morning Mr. Gilpin found, that about 120 measures of the air in 

 the bent tube had been spontaneously absorbed during the night, the quantity 

 therein being so much less than it was the preceding evening, though the elec- 

 trical machine had not been worked, or any thing done to it during the interme- 

 diate time. The reason of this in all probability is, that as the acid was then 

 corroding the mercury, the soap-lees became impregnated with nitrous air, which 

 during the night united to the dephlogisticated air, and caused the diminution. 



Though in reality the event of this experiment was such as to establish the 

 truth of my position, that the mixture of dephlogisticated and phlogisticated air 

 is converted by the electric spark into nitrous acid, as fully as if the experiment 

 had been stopped in proper time; yet, as the event was in some measure different 

 from that of my own experiments, and might afford room for cavil, I was de- 

 sirous of having it repeated; and as Mr. Gilpin was so obliging as to undertake 

 it again, the materials were, on Feb. 11, put together for a fresh experiment, in 

 the presence of most of the above-mentioned gentlemen. The soap-lees em- 

 ployed were the same as before, but 183 measures were now introduced. The 

 dephlogisticated air was different, the former parcel being all used. It was pre- 

 pared, like the former, from turbith mineral, but was rather purer, as it seemed 

 to contain only -^v of phlogisticated air. The proportion in which it was mixed 

 with common air was that of 22 to 10; so that a greater proportion of common 

 air was now used, in consequence of which it was not necessary for Mr. Gilpin 

 to introduce common air so often. 



On Feb. 1Q, the reservoir was again filled with air of the same kind, in pre- 

 sence of some of the same gentlemen. As it was found by the last experiment 

 that we must not depend on the saturation of the soap-lees being made known 

 by any alteration in the rate of diminution, the process was stopped as soon as 

 the air absorbed was such as from my own experiments I judged sufficient to 

 neutralize the soap-lees. This was effected on the 15th of March. The air 



