78 HISTORICAL INTRODUCTION TO CHEMISTRY CHAP. 



air is subject to from a mixture of iron filings and brim- 

 stone, made into a paste with water. This mixture, as I 

 have already observed, diminishes common air between 

 one-fifth and one-fourth, but has no such effect upon any 

 kind of air that has been diminished, and rendered noxious 

 by any other process ; but when it is put to a quantity of 

 nitrous air, it diminishes it so much, that no more than 

 one-fourth of the original quantity will be left." 



" Nitrous air thus diminished has not so strong a smell 

 as nitrous air itself, but smells like common air in which 

 the same mixture has stood" {Experiments on Air, 1774, 

 I. 118-119). 



Priestley was astonished to find that an agent which he 

 had employed previously to remove all the goodness from 

 common air, had actually converted the inert nitrous air 

 into a DIMINISHED NITROUS AIR " with properties which, 

 at the time of my first publication on this subject, I 

 should not have hesitated to pronounce impossible, viz. 

 air in which a candle burns quite naturally and freely, and 

 which is yet in the highest degree noxious to animals, 

 insomuch that they die the moment they are put into it " 

 (ibid., p. 215). 



As " diminished nitrous air " is soluble in cold water, it 

 was best prepared over mercury ; the gas was then almost 

 like oxygen in its power of supporting combustion. On 

 the other hand, long contact with iron over water destroyed 

 this property, the diminished nitrous air being either 

 absorbed or wholly deoxidised. Priestley found that : 



" A candle burned with an enlarged flame ... in nitrous 

 air, which had been in contact with iron in quicksilver, 

 about six months. 



" Water being admitted to the remainder of this air, it 

 began to be absorbed as usual. 



" Nitrous air, which had been confined above a year in 

 contact with iron, standing in water, was, in all respects like 

 phlogisticated common air : it neither diminished common 



