On Sal Niiruni and Nitro- Aerial Spirit 115 



not be all pumped out. Therefore if the volume of 

 the whole glass be measured by means of water put 

 into it drop by drop, and compared with the space in 

 the narrower glass which the residual air had filled^ 

 the extent to which the said air had expanded will be 

 ascertained. For by as much as the one space exceeds 

 the other, so much was the expansion of that air. 

 And from many repetitions of the experiment, I have 

 ascertained that air of that kind expands to more 

 than two hundred times its volume ; and indeed if it 

 had been relieved from the pressure of the surround- 

 ing water, it would have expanded about twice as 

 much. Nor will common air, when treated in the 

 same manner, expand more ; but it must be observed 

 that in making experiments of this kind, every pre- 

 caution must be taken that the airs, whose elastic 

 powers are to be compared with one another, are 

 pressed by an equal weight of the surrounding water, 

 and also that the pressure of the surrounding air be 

 diminished to an equal extent in every experiment, 

 by pumping. 



I note here in passing that I made an experiment 

 in a similar way, to find whether the air in which an 

 animal or a lamp had expired, possessed elastic force 

 in an equal degree with unimpaired air, and, in fact, it 

 appears to me to expand no less than any other air, as 

 was previously said. But in order that experiments 

 of this kind may be made, it is sometimes necessary 

 that the air whose elastic force is to be investigated 

 should be drawn off from the glass which contains it, 

 and transferred to the glass first described, and this 

 can be done in the following manner. Let a glass, 

 not too large, be submerged in the water in which 

 the glass is which contains the air to be drawn off, so 

 that it is filled with water ; then let this glass be 



