( 68 ) 



In 1761 he succeeded that erudite and wandering scholar, Dr. J. Aiken, 

 as teacher of languages in the Dissenting academy at Warrington, 

 where he remained for six years, and where he wrote his History of 

 Elect ri rit ii, aided by the friendly help of Franklin in respect of books — 

 a work which first brought him into notice amongst scientific men. 

 He became a Fellow of the Royal Society in 1766. In 1767 he 

 returned to Leeds, where he began his studies in pneumatic chemistry, 

 incited thereto " by living in the immediate vicinity of a brewery." It 

 would seem that the " latitude " of his views determined the Board 

 of Longitude in their decision — prompted perhaps thereto by certain 

 ecclesiastics — not to acquiesce in an arrangement whereby it was 

 agreed he should accompany Captain Cook on his second voyage. 

 Another change, and then he moved to Birmingham. 



Theology and politics for a time engaged his attention. The 

 French Revolution was in progress, Priestley's political opinions led 

 to this result, that, in a riot in 1791, " his house was burned down, and 

 he narrowly escaped with his life." He fled to London and ultimately 

 set out for America, where he died in 1804. 



Priestley's experiments on respiration begin with air infected by 

 animal respiration, and his attempts to restore it to a state of purity. 

 Here is the story in Priestley's own words : — 



" Experiments and Observations on Different Kinds of Air, by Joseph Priestley, 

 LL.D., F.R.S. — Of the restoration of air in which a candle has burned out, by vegetation. 



" It is well known that a flame cannot subsist long without change of air, so that 

 the common air is necessary to it, except in the case of substances into the composition 

 of which nitre enters; for these will burn in vacuo, in fixed air, and even under water, 

 as is evident in some rockets, which are made for this purpose. It is generally said, that 

 an ordinary candle consumes, as it is called, about a gallon in a minute. Considering 

 this amazing consumption of air, by fires of all kinds, volcanoes, <fec, it becomes a great 

 object of philosophical inquiry, to ascertain what change is made in the constitution of 

 the air by flame, and to discover what provision there is in nature for remedying the 

 injury which the atmosphere receives by this means. 



" Though this experiment failed, I have been so happy, as by accident to have hit 

 upon a method of restoring air, which has been injured by the burning of candles, and 

 to have discovered at least one of the restoratives which nature employs for this purpose. 

 It is vegetation. This restoration of vitiated air, I conjecture, is effected by plants 

 imbibing the phlogistic matter with which it is overloaded by the burning of inflammable 

 bodies. But whether there be any foundation for this conjecture or not, the fact is, I 

 think, indisputable. I shall introduce the account of my experiments on this subject, by 

 reciting some of the observations which I made on the growing of plants in confined air, 

 which led to this discovery." 



"One might have imagined that, since common air is necessary to vegetable as well 

 as animal life, both plants and animals had affected it in the same manner, and I own I 

 had that expectation when I first put a sprig of mint into a glass jar, standing inverted 

 in a vessel of water ; but when it had continued growing for some months, I found that 

 the air would neither extinguish a candle, nor was it at all inconvenient to a mouse 

 which I put in. The plant was not affected any otherwise than was the necessary 

 consequence of its confined situation, for plants growing in several other kinds of air 

 were all affected in the very same manner." 



