OF PNEUMATICS. 227 



the bulk of the apples themselves ; so that its pressure LECT 

 was equal to 11776 pounds, and in a cubic inch of oak, to ^x^^x 

 19860 pounds against their sides. So that if the air was 

 let loose at once in these substances, they would tear 

 every thing to pieces about them with a force superior to 

 that of gunpowder. Hence, in eating apples, it is well 

 that they part with the air by degrees, as they are 

 chewed, and ferment in the stomach, otherwise an apple 

 would be immediate death to him who eats it. 



The mixing of some substances with others will release 

 the air from them, all of a sudden, which may be at- 

 tended with very great danger. Of this we have a re- 

 markable instance in an experiment made by Dr. Slare; 

 who having put half a dram of oil of carraway seed 

 into one glass, and a dram of compound spirit of nitre 

 in another, covered them both on theair-puuip, with a 

 receiver, six inches wide, and eight inches deep, and then 

 exhausted the air, and continued pumping until all that 

 could possibly be got both out of the receiver, and out of 

 the two fluids was extricated, then, by a particular con- 

 trivance from the top of the receiver, he mixed the 

 fluids together ; upon which they produced such a pro- 

 digious quantity of air, as instantly blew up the receiver, 

 although it was pressed down by the atmosphere with 

 upwards of 400 pounds weight. 



N. B. In the 28th experiment, the cork must be 

 covered all over with a piece of thin wet bladder glued 

 to it, and not used until it be thoroughly dry. 



