vn] of the Seventeenth Century. 189 



For every combustion there is needed on the one hand 

 sulphureous (combustible) material, and on the other hand 

 igneo-aereal particles. Now there are no sulphureous par- 

 ticles in nitre, hence nitre will not burn by itself. But nitre 

 as just stated when mixed with sulphureous particles burns 

 most readily, even without the access of air. 



He conclu'des that the aereal part of nitre is nothing else 

 than the igneo-aereal particles of which he has been speaking 

 as essential to combustion ; these particles exist, not in the sal 

 alkali part of the nitre, but in the spiritus acidus part ; and he 

 enters into an explanation why the whole nitre, spiritus acid 

 and sal alkali together, is better suited for burning than the 

 spiritus acidus itself, though this really contains the elements 

 essential to combustion. 



It is obvious from the above that Mayow, by his nitro-aereal 

 or igneo-aereal salt or spirit meant nothing less than that which 

 we for a hundred years or more have been calling oxygen. And 

 he thus, with clear insight, sums up the conditions necessary for 

 combustion to take place : 



" Concerning fire (combustion) it must be noted that for the 

 "ignition of this it is necessary that igneo-aereal particles 

 " should either preexist in the thing to be burnt or should be 

 "supplied from the air. Gunpowder is very easily burnt by 

 " itself by reason of the igneo-aereal particles existing in it. 

 " Vegetables are burnt partly by means of the igneo-aereal 

 11 particles existing in them, partly by help of those brought to 

 " them from the air. Purified sulphureous matter on the con- 

 " trary can be burnt only with the help of igneo-aereal particles 

 " brought to it by the air." 



He also recognized that in combustion the igneo-aereal 

 particles enter into combination with the substance burnt. 

 In the course of this discussion on burning he makes the 

 following very remarkable reflection. He was writing in 1668. 

 Many years afterwards in 1697 Stahl as I have said introduced 

 the phlogiston theory. The essence of that theory was the view 

 that when a combustible body, a phlogisticated body, underwent 

 combustion, phlogiston departed from it; the body suffered a 

 loss, it became dephlogisticated. The world had to wait for 



