436 Mr. Anderson [April 9, 



WEEKLY EVENING MEETING, 



Friday, April 9, 1886. 



Sir William Bowman, Bart. LL.D. F.R.S. Vice-President, 

 in the Chair. 



William Anderson, Esq. M. Inst. C.E. 3LB.L 



On New Applications of the Meclianical Properties of Cork to the Arts. 



It would seem difficult to discover any new properties in a substance 

 so familiar as cork, and yet it jDossesses qualities which distinguish it 

 from all other solid or liquid bodies, namely, its power of altering 

 its volume in a very marked degree in consequence of change of 

 pressure. All liquids and solids are capable of cubical compression, or 

 extension, but to a very small extent ; thus water is reduced in volume 

 by only one two-thousandth part by the pressure of one atmosphere. 

 Liquid carbonic acid yields to pressure much more than any other 

 fluid, but still the rate is very small. Solid substances, with the 

 exception of cork, offer equally obstinate resistance to change of bulk, 

 even indiarubber, which most people would suj^pose capable of very 

 considerable change of volume, we shall find is really very rigid. 



I have here an apparatus for applying pressure by means of a 

 lever. I place a piece of solid indiarubber under the plate 

 and you see that I can compress it considerably by a very light 

 pressure of my finger. I slip this same piece of indiarubber into a 

 brass tube, which it fits closely, and now you see that I am unable to 

 compress it by any force which I can bring to bear, I even hammer 

 the lever with a mallet and the blow falls as it would on a stone. 

 Tlie reason of this phenomenon is, that, in the first place, with the 

 indiarubber free, it spread out laterally while being compressed 

 longitudinally, and consequently the volume was hardly altered at all ; 

 in the second case, the strong brass tube prevented all lateral exten- 

 sion, and because indiarubber is incapable of appreciable cubical com- 

 pression, its length only could not be sensibly altered by pressure. 



Extension, in like manner, does not alter the volume of indiarubber. 

 In this glass tube is a piece of solid round rubber which nearly fills 

 the bore. The lower end of the rubber is fixed in the bottom of the 

 tube and the upper end is connected by a fine cord to a small wind- 

 lass, by turning which I can stretch the rubber. I fill the tube to 

 the brim with water and throw an image of it on to the screen. If 

 stretching the rubber either increases or diminishes its volume, the 

 water in the tube will either overflow or shrink in it. I now stretch 

 the rubber to about 3 inches, or one-third of its original length, but 

 you cannot see any ai^preciable movement in the water-level, hence 

 the volume of the rubber has not changed. 



