190 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



I could let up any quantity of soap-lees, or any other liquor 

 which I wanted to be in contact with the air." 



" The bore of the tube M used in most of the following 

 experiments was about one-tenth of an inch ; and the 

 length of the column of air, occupying the upper part of the 

 tube, was in general from i J to f of an inch." 



" When the electric spark was made to pass through 

 common air, included between short columns of a solution 

 of litmus, the solution acquired a red colour, and the air 

 was diminished, conformably to what was observed by 

 Dr. Priestley." 



" When lime-water was used insteadof the solution of litmus, 

 and the spark was continued till the air could be no further 

 diminished, not the least cloud could be perceived in the 

 lime-water : but the air was reduced to two-thirds of its 

 original bulk ; which is a greater diminution than it could 

 have suffered by mere phlogistication, as that is very little 

 more than one-fifth of the whole." 



" When the air is confined by soap-lees, the diminution 

 proceeds rather faster than when it is confined by lime- 

 water ; for which reason, as well as on account of their 

 containing so much more alkaline matter in proportion to 

 their bulk, soap-lees seemed better adapted for experiments 

 designed to investigate the nature of this acid, than lime- 

 water" (A.C.R. III. 39-43). 



Cavendish found that the diminution of volume on 

 sparking either azote or pure oxygen separately over soap- 

 lees was very small ; but when five parts of oxygen " were 

 mixed with three parts of common air, 1 almost the whole of 

 the air was made to disappear " (A.C.R. III. 44). The soap- 

 lees " being evaporated to dryness, yielded I T %- grains of salt, 

 which is pretty exactly equal in weight to the nitre which that 

 quantity of soap-lees would have afforded if saturated with 

 [nitric] acid. This salt was found, by the manner in which 

 paper dipped into a solution of it burned, to be true nitre " 



1 In this experiment 5 + (i x 3) = 5 ^ volumes of oxygen combined 

 with 1x3 = 2-2; volumes of azote, i.e. 7 volumes of oxygen combined 

 with 3 of azote. 



