6 The Hon. Sir Charles Parsons [Jan. 23, 



a high temperature may be very violent if suddenly released by the 

 melting of the pole pieces; also some endothermic compounds have 

 been formed which swelled the container and allowed the contents to 



pe. 



My experiments confirmed the conclusion at which Threlfall had 

 independently arrived, thai under pressures up to 100 tons per square 

 inch, and very intense heating by electrical current, graphite is not 

 materially changed. But modifications in the experiments were 

 made, and other methods adopted, as will be explained, which in 

 some respects carried the investigation to still higher pressures and 

 temperatures; these however lead to the same conclusion. 



This evening 1 propose to deal to some extent with the practical 

 or engineering side of the subject, and to review the limits of pressure 

 and temperature which are artificially attainable, and to make some 

 comparison between them and the pressures and temperatures occur- 

 ring in nature. 



When the blade of a knife is pressed strongly against another 

 blade so as to make a dent in each, the pressure on the boundary 

 surface of the metal at the notch will have averaged from 800 to 

 350 tons per square inch, according to the hardness of temper of the 

 Bteel. The pressures on the knife edges of a weighing machine 

 when fully loaded are also of the same order. 



When a needle is broken, or a piece of piano wire is strained to 

 the point of breaking, the maximum tension on the metal will be at 

 at the rate of 150 tons per square inch. 



On the other hand, the pressures that occur in the chambers of 

 large guns do not usually exceed 20 tons per square inch, and the 

 tensile stress on the plates of a ship in heavy weather should not 

 exceed 8 tons per square inch. 



From these simple instances some idea is gathered of the limita- 

 tion- imposed by materials and dimensions upon apparatus for 

 experimenting at high pressures because of the practical difficulty 

 of hardening and tempering steel in large masses. 



When dealing with small amounts of material in each experiment 

 the dimensions allow of the container and the ram being made of 

 tungsten steel, which is a material that can be hardened and tempered 

 throughout, and not only superficially as in the case of ordinary carbon 

 steel. Th<' material is hard and strong, but not brittle, and it retains 

 these qualities up to moderate temperatures, such as 600 0., to a much 

 greater extent than any other steel. Fig. 1 shows a container or die 

 the bore is \ ! 2 inches in diameter, and it may he used for a limited 

 number of times for a pressure of 200 tons per square inch. It will 

 however eventually crack if this pressure is many times repeated, the 

 cracks usually beginning near the bottom of the die. 



For still higher pressures it is better to use a double re-entrant 

 container (Fig. '1). witu two rams, J inch in diameter ; both the con- 

 tainer and the rams are made of hardened and tempered tungsten steel, 



