558 I'HILOSOPHICAL TRANSACTIONS. [anNO 178Q. 



the vapour of the acid excluded about V^ of the quantity. Having sealed the 

 tube hermetically, I shut it up in a gun barrel, in the manner above mentioned, 

 and exposed it to a boiling heat for several hours, and then opening it under water, 

 there came out of it 2.03 ounces measures of air, very turbid and vi^hite; and 

 when examined, it appeared to be of the standard of 1.02, with 2 equal measures 

 of nitrous air; when with 1 measure of the same nitrous air the standard of the 

 common air was 1.07- 



In order to exclude all air from the contact of the acid, I made a quantity of 

 it to boil in the tube, and when the vapour had expelled all the air, I sealed it 

 hermetically, in the manner in which water hammers are made; and then ex- 

 posing it to heat, found that it acquired as high a colour as when air had been 

 confined along with it; so that it is evident, that air is not necessary to this effect. 

 When the tube was opened under water, a quantity of dephlogisticated air 

 rushed out, exceedingly white as before; but when I examined it, I found it to 

 be of the standard of only 0.66. When this impurity is considered, it will ap- 

 pear, that when much air is yielded in this process, some phlogisticated air may 

 have been imbibed, though, computing in the manner above mentioned, the 

 phlogisticated air after the process should be in greater quantity than was con- 

 tained in the tube before it, as was the case in the following experiment. In a 

 glass tube which, besides the acid, contained 1.13 oz. m. of common air, I ex- 

 posed colourless spirit of nitre to heat till it became of a deep orange colour; and 

 when it was opened under water, there came out of it 2.83 oz. m. of air exceed- 

 ingly turbid, of the standard of 0.66, with 2 equal quantities of nitrous air, 

 when that of the common air, with one equal quantity of nitrous air, was I.07. 

 Computing in the manner above mentioned, there was in the tube before the 

 process O.7477 oz. m. of phlogisticated air, and after the process 0.8792 oz. m. 

 But the dephlogisticated air, amounting to I.7 oz. m. being of the standard of 

 0.66, will be found to contain O.374 oz. m. of phlogisticated air, which being de- 

 ducted from 0.8792, there will remain only 0.5052 oz. m. which is considerably 

 less than 0.7477 oz. m. 



Having repeatedly observed, that the acid became coloured in consequence of 

 being exposed to heat in contact with any kind of air whatever, I exposed at the 

 same time, and in the same circumstances, 3 equal quantities of the same colour- 

 less spirit of nitre, in 3 nearly equal tubes, one containing dephlogisticated, an- 

 other phlogisticated, and a 3d inflammable air; that, if there should be any 

 difference in the colouring of the acid in these cases, it might be the more easily 

 perceived. But though I gave all the attention that I could, I did not perceive 

 that there was any difference, except what arose from some of the tubes being 

 placed a little nearer the fire than the rest; and, by changing their places, the 

 colour was at length the very same in them all. 



As the spirit of nitre can be rendered smoking, or phlogisticated, by the mere 



