WOI1I 



The Hon. Sir Charles Parsons [Jan. 23, 



When sinking the deeper portions of the shaft probably shields 



ild be necessary bo protect t he miners from the splinting of the 

 rock which is caused by the intense compressive stress which splits 

 off scales Prom the surface, sometimes with considerable violence. 



In l'.un the estimate of the time required to sink 12 miles was 

 eighty yearsand was based on the records at that time. With improved 

 machinery and methods the records have been so much lowered (at 

 the Crown mines 310 feet of a circular 20 feet die-shaft have been 

 sunk in a month) that an estimate of thirty years seems now to be 

 reasonable. 



ThrelfaU traced the gradual evolution of the theory of the effects 

 of temperature and pressure on the allotropic forms of various 

 substances, their critical temperatures and conditions of gaseous, 

 liquid and fluid states. He described his apparatus and experiments 

 designed to melt graphite under high pressure, his inference being, 

 that under pressures up to 100 tons per square inch carbon does not 

 follow the same law as many other substances, and does not crystallize 

 as diamond on cooling. 



An interesting discovery was made by Bridgeman in 1911 when 

 Btudying the compressibility of mercury. He found that it had a 

 remarkable power of penetrating steel containers, more especially 

 those made of hardened and tempered steel ; a power not possessed 

 by oil or water, and which caused them to burst at much lower 

 pressures than when they were charged with oil or water. The 

 phenomenon he attributed to the fact that mercury has the power of 

 dissolving small percentages of iron, and will amalgamate with it when 

 the surfaces are absolutely free from oxide. 



In 1912 Bridgeman published his remarkable researches on water 

 under pressures up to 20,000 atmospheres. He found that there are 

 four allotropic forms of ice besides ordinary ice, which are found 

 under various conditions of pressure and temperature with determinate 

 regions of stability. All these forms, except ordinary ice, are more 

 dense than water. One of these forms is remarkable as existing from 

 a temperature of 18 C. under a pressure of 4500 atmospheres up to 

 temperature of 07 C. under a pressure of 20,000 atmospheres. 



Recently a pressure of from 200 to 1000 atmospheres at a 

 temperature between 500 and Ton C. has been applied to compel 

 hydrogen to combine with nitrogen to form ammonia on a great 

 commercial scale ; a calylist being necessary to promote the com- 

 bination and to establish the equilibrium between the gases and 

 their product. This action is reversible as regards temperature 

 and pressure. On the other hand, iron just molten is an energetic 

 calylist in the transformation of diamond into graphite, but contrary 

 to expectations, as we shall see, no amount of pressure that has as 

 yet been applied appears to haw caused a reversal of this action. 



Moiv than thirty years ago. having suitable apparatus at hand, I 

 made a few experiments to try the effect of high pressures and 



