Ifif PHILOSOPHICAL TRANSACTIONS. [annO 1/85. 



Having made these previous trials, I introduced into the tube a little soap-lees, 

 and then let up some dephlogisticated and common air, mixed in the above-men- 

 tioned proportions, which rising to the top of the tube m, divided the soap-lees 

 into its two legs. As fast as the air was diminished by the electric spark, I con- 

 tinued adding more of the same kind, till no further diminution took place : after 

 which a little pure dephlogisticated air, and after that a little common air, were 

 added, in order to see whether the cessation of diminution was not owing to some 

 imperfection in the proportion of the two kinds of air to each other ; but without 

 effect.* The soap-lees being then poured out of the tube, and separated from 

 the quicksilver, seemed to be perfectly neutralized, as they did not at all dis- 

 colour paper tinged with the juice of blue flowers. Being evaporated to dryness, 

 they left a small quantity of salt, which was evidently nitre, as appeared by the 

 manner in which paper, impregnated with a solution of it, burned. 



For more satisfaction, I tried this experiment over again on a larger scale. 

 About 5 times the former quantity of soap-lees were now let up into a tube of a 

 larger bore; and a mixture of dephlogisticated and common air, in the same pro- 

 portions as before, being introduced by the apparatus represented in fig. 6, the 

 spark was continued till no more air could be made to disappear. The liquoi*, 

 when poured out of the tube, smelled evidently of phlogisticated nitrous acid, and 

 being evaporated to dryness, yielded 1^ gr. of salt, which is pretty exactly equal 

 in weight to the nitre which that quantity of soap-lees would have afforded if 

 saturated with nitrous acid. This salt was found, by the manner in which paper 

 dipped into a solution of it burned, to be true nitre. It appeared, by the test of 

 terra ponderosa salita, to contain not more vitriolic acid than the soap-lees them- 

 selves contained, which was excessively little ; and there is no reason to think that 

 any other acid entered into it, except the nitrous. 



A circumstance however occurred, which at first seemed to show that this salt 

 contained some marine acid ; namely, an evident precipitation took place when a 

 solution of silver was added to some of it dissolved in water ; though the soap-lees 

 used in its formation were perfectly free from marine acid, and though, to pre- 

 vent all danger of any precipitate being formed by an excess of alkali in it, some 

 purified nitrous acid had been added to it, previous to the addition of the solution 

 of silver. On consideration however I suspected that this precipitation might 



• From what follows it appears, that the reason why the air ceased to diminish was, that as the 

 soap-lees were then become neutralized, no alkali remained to absorb the acid formed by the opera- 

 tion, and in consequence scarce any air was turned into acid. The spark however was not continued 

 long enough after the apparent cessation of diminution, to determine with certainty, whether it was 

 only that the diminution went on remarkably slower than before, or that it was almost come to a 

 stand, and could not have been carried much fiirther, though I had persisted in passing the sparks.— • 

 Orig. 



