VOL. LXXII.] PHILOSOPHICAL TRANSACTIONS. 255 



gradually applied and raised to the utmost, afford 83.87 cubic inches of nitrous 

 air. And as this nitrous air contains nearly the whole quantity of phlogiston 

 which iron will part with (it being more completely dephlogisticated by this acid 

 than by any other means) it follows, that 83.87 cubic inches of nitrous air con- 

 tain at least 5,42 gr. of phlogiston ; but it may reasonably be thought that the 

 whole quantity of phlogiston which iron will part with, is not expelled by the 

 vitriolic acid, and that nitrous acid may expel and take up more of it. To try 

 whether this was really so, I calcined a certain quantity of green vitriol, till its 

 ferruginous basis was quite insipid ; I then extracted from 64 gr. of this ochre 2 

 cubic inches of nitrous air, consequently 100 gr. of this ochre would give 3.12 

 cubic inches of nitrous air; and if 83.87 cubic inches of nitrous air contain 

 5.42 of phlogiston, then 3.12 cubic inches of this air contain 0.2 of a grain of 

 phlogiston; consequently, nitrous acid extracts from 100 gr. of iron, -^ of a 

 grain more phlogiston than the vitriolic acid does ; therefore 83.87 cubic inches 

 of nitrous air, containing nearly all the phlogiston which iron gives out, contain 

 5.62 gr. of phlogiston. Then 100 cubic inches of nitrous air contain 6.7 gr. of 

 phlogiston, and since 100 cubic inches of nitrous air weigh 39.9 gr. they must 

 also contain 33.2 gr. of nitrous acid. Also, 100 gr. of nitrous air contain 

 16.792 of phlogiston, and 83.208 of acid. 



When first I made these experiments I imagined, that the nitrous air thus 

 expelled contained all the phlogiston of the metals dissolved in the nitrous acid, 

 as this acid is well-known to dephlogisticate metals as perfectly as possible ; but 

 I soon observed, as did Dr. Priestley and Mr. Fontana, that the greater part of 

 this is air resorbed and detained in the solution, the acid and calx having, accord- 

 ing to the beautiful remark of Mr. Scheele, a greater attraction to phlogiston 

 than either separately ; yet that the calculation is nearly just, will appear clearly 

 in my next paper, by its coincidence with the quantity of phlogiston discovered 

 in lead by Dr. Priestley and that which is contained very evidently in regulus of 

 arsenic, silver, and quicksilver. 



Of the quantity of phlogiston infixed air. — Before I attempt to determine this 

 quantity, it will be necessary to prove that it contains any ; and for this purpose 

 minutely to examine its nature and origin. Dr. Priestley first discovered, that 

 in all processes, in which phlogiston is disengaged from any substance, as in 

 combustion, respiration, calcination of metals, putrefaction, decomposition of 

 nitrous air by respirable air, &c. fixed air is precipitated from the common or de- 

 phlogisticated air in which these processes are performed, and that these last airs 

 are diminished both in weight and bulk, and are afterwards less fit, or absolutely 

 unfit, for these processes, according to the quantity of phlogiston that was set 

 loose. These facts are admitted by all, let their systems be what they may. 

 However, Dr. Priestley thinks he has seen one exception to this general rule ; 



