502 Rev.W.V. Harcourt on Lord Brougham's statements 



repeated, with a small variation of circumstances, and with 

 almost the same result." He takes no notice of the distinc- 

 tion established in Cavendish's paper between "fixed air," 

 and M common air in which candles have burnt or which has 

 passed through the fire;" and so entirely does he misunder- 

 stand, or disregard, Cavendish's intimation of the relative 

 levity of the latter when purified from fixed air by caustic 

 potash, as to "conclude, after making several trials, that the 

 air in which candles have burned " (without having been sub- 

 jected to such purification) "is rather lighter than common 

 air*'" whilst with regard to the lost air, which the paper 

 communicated to him described as " absorbed by the fumes of 

 the burning charcoal" he represents Cavendish as having 

 ascribed that loss to the " destruction of common air." 



Though Priestley however here proves himself not to have 

 been, as you imagine, the discoverer of nitrogen, this indi- 

 stinct, but fruitful, experimenter gave in the same document 

 three original and pregnant notifications ; for he announced 

 in it — 1. the effect of vegetables in restoring the respirable 

 quality of the air ; 2. the application of the known absorbing 

 power of nitrous gas, as a test of that respirable quality; 

 3. his observation that candles burn with an enlarged flame 

 in the gas produced by the distillation of nitre f. This ob- 

 servation it is from which those who call him the discoverer 

 of oxygen should date the discovery: for he knew as much 

 of the gas from nitre in 1772 as of that from minium in 1774- ; 

 and it was the application of nitrous gas here stated, which 

 led, in 1780, in the hands of Cavendish, to the first accurate 

 analysis of the atmosphere, and in 1781 to the solution of the 

 great problem — what becomes of the air lost in the combustion 

 of hydrogen gas ? 



In scientific value doubtless there can be no comparison 

 between the experimental inductions of Cavendish, or La- 



* " I could not find any considerable difference in the specific gravity of 

 the air in which candles or brimstone had burnt out. I am satisfied how- 

 ever that it is not heavier than common air, which must have been munifest 

 if so great a diminution of the quantity had been owing, as Dr. Hales and 

 others supposed, to the elasticity of the whole mass being impaired. After 

 making several trials for this purpose I concluded that air thus diminished 

 in bulk is rather lighter than common air." — Phil. Trans. 1772, p. 164. 



f " All the kinds of factitious air on which I have yet made the experi- 

 ment are highly noxious, except that which is extracted from saltpetre or 

 alum ; but in this even a candle burned just as in common air. In one quan- 

 tity which I got from saltpetre a candle not only burned, but the flame was 

 increased, and something was heard like a hissing, similar to the decrepita- 

 tion of nitre in an open fire ; this experiment was made when the air was 

 fresh made, and while it contained some particles of nitre which it would 

 probably have deposited afterwards." — Phil. Trans. 1772, p. 245. 



