Oil Sal Nitrum and Nitro-Aerial Spirit 9 



food. For since there is more room for receiving the 

 smoke in the empty glass than in the glass that is full 

 of air, the lamp would go out in the latter sooner than 

 in the former, if its extinction were due to the smoke. 

 Besides, no sulphureous matter, if placed in a glass 

 from which the air has been pumped, can be kindled 

 either by ignited charcoal or iron, or by the solar rays 

 collected by means of a burning-glass ; so that there 

 can be no doubt whatever that certain aerial particles 

 are quite indispensable to the production of fire, and, 

 indeed, it is our opinion that these are mainly instru- 

 mental in the production of fire, and that the shape 

 of the flame is mainly dependent upon these, 

 thrown into extremely brisk motion, as will be ex- 

 plained at greater length below. But it is not to be 

 supposed that the air itself, but only that its more 

 active and subtle part is the igneo-aerial food, since a 

 lamp enclosed in a glass goes out when there is still 

 an ample enough supply of air in it, for neither is it 

 to be believed that the particles of air which existed 

 in the said glass are annihilated by the burning of the 

 lamp, nor yet that they are dissipated, since they are 

 unable to penetrate the glass. Further, it is impos- 

 sible that these igneo-aerial particles are any perfect 

 nitre, as is generally supposed — for it was already 

 pointed out that not the very nitre as a whole, but 

 only a certain part of it, resides in the air. 



In the second place, it would be reasonable to suppose 

 that the igneous particles of air necessary to the support 

 of all flame reside in sal nitrum and constitute its more 

 active and fiery part, for it is to be noted that nitre 

 mixed with sulphur deflagrates readily enough in a 

 glass which does not contain air, and also under water, 

 as will be established by the following experiment ; 

 for let gunpowder, very finely ground, be made 



