1886.] on New Applications of the Mechanical Properties of Cork. 445 



which were necessary to compress the cork to the corresjDonding 

 volume. Thus to reduce the volume to one-half, required a pressure 

 of 250 pounds per square inch. At 1000 pounds per square inch the 

 volume was reduced to 44 per cent., the yielding then became very 

 little, showing that the solid parts of the cells had nearly come 

 together, and this corroborates Mr. Ogston's determination, that the 

 gaseous part of cork constitutes 53 per cent, of its bulk. The 

 engineer, in dealing with a compressible substance, requires to know 

 not only the pressure which a given change of volume produces, but 

 also the work which has to be expended in producing the change of 

 volume. The work is calculated by multiplying the decrease of 

 volume by the mean pressure per unit of area which produced it. 

 The ordinates of the dotted curve on the diagram with the corre- 

 sponding scale of foot pounds on the right-hand side are drawn equal 

 to the work done in compressing a cubic foot of cork to the several 

 volumes marked on the base line. I have not been able to find 

 an equation to the pressure curve, it seems to be quite irregular, and 

 hence the only way of calculating the effects of any given change of 

 volume is to measure the ordinates of the curve constructed by actual 

 experiment. As may be supposed the pressures indicated by ex- 

 periment are not nearly so regular and steady as corresponding 

 experiments in a gas would be, and the actual form of the curves 

 will depend on the quality of the cork experimented on. 



The last point of importance in this inquiry relates to the 

 permanence of elasticity in cork. 



So far as preservation of elasticity during years of compression 

 is concerned, we have the evidence of wine corks to show that a 

 considerable range of elasticity is retained for a very long time. 

 With respect to cork subjected to repeated compression and exten- 

 sion, I have very little evidence to offer beyond this, that cork which 

 had been compressed and released in water many thousand times, 

 had not changed its molecular structure in the least, and had con- 

 tinued perfectly serviceable. Cork which has been kept under a 

 pressure of three atmospheres for many weeks appears to have shrunk 

 to from 80 to 85 per cent, of its original volume. 



I will conclude this lecture by bringing under your notice two 

 novel applications of cork to the arts. 



Before the lecture-table stands a water-raising apparatus called 

 a hydraulic ram. The structure of the machine is shown by a diagram 

 on the wall, Eig. 4. The ram consists of an inclined pipe A, which 

 leads the water from a reservoir into a chamber B, which terminates in 

 a valve C, opening inwards. Branching up from the chamber is a 

 passage leading to a valve D, opening outwards and communicating 

 with a regulating vessel E, which is usually filled with air, but which 

 I prefer to fill with cork and water. Immediately beyond the inner 

 valve, is inserted a delivery pipe F, which is laid to the spot to which 

 the water has to be pumped, in this case to the fountain jet in the 

 middle of this pan. 



