Ofi Sal Nitrum and Nitro- Aerial Spirit 83 



■nitre, no mean supply of air is required, but that so 

 much should be imprisoned in a small piece of nitre is 

 very unlikely, especially as it is only such air as is 

 possessed of a very high degree of elasticity that is 

 suitable for the production of flame. But these points 

 will be still further established by the following experi- 

 ment. 



For instance, let spirit of nitre and also salt of tartar, 

 or any other fixed salt dissolved in a small quantity of 

 distilled water, be placed in separate glass vessels and 

 •enclosed in another sufl5ciently large glass vessel from 

 which the air is afterwards exhausted, as far as possible, 

 by means of an air-pump (indeed in the experiment 

 made by me the air was almost entirely pumped out). 

 When this is done, if any aerial or elastic substance 

 be present mixed with the aforesaid liquids, it will 

 escape in the form of bubbles when the pressure of 

 the ambient air is withdrawn. When the bubbles, if 

 there be any, no longer escape from the liquids (for it 

 is to be observed that from nearly every liquid when 

 in a place void of air small bubbles are wont to rise) 

 let the aforesaid liquids be mixed, and an intense 

 effervescence will immediately be produced. Let 

 everything remain in this condition until the action 

 has entirely ceased, and then, lastly, let the mixture be 

 removed and evaporated at a mild heat to the dryness 

 of salt, and so at the bottom of the glass we shall find 

 nitre generated in an airless place, which in accordance 

 with the nature of nitre will, if placed on a burning 

 coal burst into flame ; and yet it is by no means to be 

 supposed that air is present in nitre produced in this 

 way. Further, if nitre itself dissolved in distilled water 

 be put in a place empty of air, air in the form of 

 bubbles scarcely escapes at all from the solution — 

 •certainly in a less degree than from common water — 



