444 



Mr. Anderson 



[April 9, 



and pressure be then applied, minute bubbles will be found to collect 

 on the surface, and their formation will go on for many hours. 



On the other hand, if cork be subjected to pressure from all sides, 

 such as operates when it is immersed in water under pressure, then 

 the cells are supported in all directions, the air in them is reduced in 

 volume, and there is no tendency to escape in one direction more than 

 another. An indiarubber bag, such as this, distended by air, bursts, 

 as you see, if pressed between two surfaces, but if an indiarubber cell 

 be placed in a glass tube and subjected to hydraulic pressure, it is 

 merely shrivelled up, the strain on its walls is actually reduced. 



To take advantage of the peculiar properties of cork in mechanical 

 applications, it is necessary to determine accurately the law of its 

 resistance to compression, and for this purpose I instituted a series of 

 experiments of this kind. Into a strong iron vessel of 5J gallons 

 capacity I introduced a quantity of cork, and filled the interstices full 

 of water, carefully getting out all the air. I then proceeded to 

 pump in water, until definite pressures up to 1000 pounds per square 

 inch had been reached, and, at every 100 pounds, the weight of water 



Fig. 3. 



'^^ Volume of Cork. 



pumpecl in was determined. In this way, after many repetitions, I 

 obtained the decrease of volume, due to any given increase of pressure. 

 The observations have been plotted into the form of a curve. Fig. 3, 

 which you see on the diagram on the wall. The base-line reiDresents a 

 cylinder containing one cubic foot of cork divided by the vertical 

 lines into ten parts ; the black horizontal lines according to the scale 

 on the loft hand represent the pressures in pounds per square inch 



