Mr. G. F. Rodwell on the Theory of Phlogiston, 17 



never sufficiently applauded. The theory is propounded in 

 twelve propositions : the pith of it is given below in Hooke's own 

 words ; and it cannot be better preluded than by his assertion, 

 " This hypothesis I have endeavoured to raise from an infinity 

 of observations and experiments." 



"Firstly, that the air in which we live, move, and breathe, 

 and which encompasses very many, and cherishes most bodies 

 that it encompasses, that the air is the menstruum of all sulphu- 

 reous bodies." 



"Secondly, that this action it performs not until the body be 

 first sufficiently heated." 



"Thirdly, that this action of dissolution produces or generates 

 a very great heat, and that which we call/n?." 



"Fourthly, that this action is performed with so great a violence, 

 and does so minutely act, and rapidly agitate the smallest parts 

 of the combustible matter, that it produces in the diaphanous 

 medium of the air the action or pulse of light." 



"Fifthly, that the dissolution of sulphureous bodies is made 

 by a substance inherent and mixed with the air, that is like, if 

 not the very same with that which is fixed in saltpeter, will, I 

 think, readily be demonstrated." 



" Tenthly, that the dissolving parts of the air are but few .... 

 whereas saltpeter is a menstruum, when melted and red hot, that 

 abounds more with those dissolvent particles, and therefore as a 

 small quantity of it will dissolve a great sulphureous body, so 

 will the dissolution be very quick and violent." 



" Twelfthly, it seems reasonable to think that there is no such 

 thing as an element of fire that should attract or draw up the 

 flame, or toward which the flame should endeavour to ascend out 

 of a desire or appetite of uniting with that as its homogeneal 

 and primitive or generating element; but that that shining 

 transient body which we call flame is nothing else but a mixture 

 of air and volatile sulphureous parts of dissoluble or combustible 

 bodies, which are acting upon each other whilst they ascend; 

 that is, flame seems to be a mixture of air, and the combustible 

 volatile parts of any body, which parts the encompassing air does 

 dissolve or work upon." 



This theory was adopted by John Mayow*, who enlarged it 

 by a number of highly ingenious experiments which clearly 

 showed the part which air plays in combustion, together with 

 the compound nature of air. He further proved that one of the 

 constituents of the air is the supporter of life and combustion, 

 and the cause of putrefaction ; he also assumed it to be the 

 principle of acidity. These experiments were published many 

 years before Stahl wrote on phlogiston. 



* Born 1645, died 16/6. 



Phil. Mag. S. 4. Vol. 35. No. 234. Jan. 1868. C 



