68o 



NATURE 



[February 19, 1920 



The material is hard and strong, but not brittle, and 

 it retains these qualities up to moderate temperatures,^ 

 such as 600° C, to a much greater extent than any 

 other steel. 



In one form of container or die the bore is \\ in. 

 in diameter, and it may be 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 tlie die. 



For still higher pressures it is better to use a 

 double re-entrant container with two rams J in. in 

 diameter. Both the container and the rams are made 

 of hardened and tempered tungsten steel, and are 

 rendered fiuid and gastight by mild steel cups on the 

 ends of the rams. 



If the charge occupies only a short length of the 

 bore, as shown, the barrel of the container where the 

 charge lies is supported by the shear strength of the 

 metal above and below the zone of pressure in addi- 

 tion to its own strength as a tube. Under these 

 conditions it is as strong as or stronger than the crush- 

 ing strength of the rams, and pressures of 300 tons 

 per square inch may be repeated several times without 

 cracking. 



In a container of this form seven grains of ful- 

 minate of mercury have been placed, embedded in 

 graphite, and the pressure increased very gradualljf 

 until it reached 230 tons per square inch (under this 

 treatment fulminate does not usually detonate). The 

 die was then heated by gas to more than 180° C, the 

 temperature of detonation. After two failures of the 

 experiment, owing to the leakage of the steel cups, 

 the third was successful, and no gas escaped and the 

 container was uninjured. The graphite was some- 

 what caked, but otherwise unaltered. Graphite mixed 

 with sodium nitrate and fulminate was also exploded 

 under the same conditions. Graphite with 15 per 

 cent, of potassium chlorate detonated when 200 tons 

 per square inch had been reached. 



Many other reactions were tested in a similar 

 manner in larger dies under pressures of from 40 to 

 200 tons. The action of concentrated sulphuric acid 

 on sugar was accelerated by a pressure of 50 tons, 

 but, on the whole, these experiments in dies failed 

 to produce any interesting results. 



Unfortunately, the heating of the die with its 

 charge cannot be carried much above 500° C. 

 without serious weakening of the steel and com- 

 pelling a reduction of pressure. The electrical 

 heating of the charge in such small dies, while 

 keeping the die cool, presents great difficulties in 

 electrical insulation on so small a scale to withstand 

 intense pressure, but I think that it might be 

 accomplished in certain instances. 



It has been suggested, with the object of reachinc 

 higher pressures, that a small die might be bodilv 

 immersed in a large container. Doubtless it could 

 be arranjTfed, but it would be verv cumbersome to 

 work with, and would only add about 100 tons per 

 square inch to the maximum pressure. 



A better plan would be to follow the principle of 

 the usual capped armour-piercing projectile, and to 

 reinforce the rams and ends of the container bv 

 tightly fitting copper or bronze rings around the necks 

 of the rams, keeping the parallel part of the noses 

 as short as possible. 



When in operation the copper rings will be flattened 

 and squeezed against the necks and shoulders of the 

 rams, and also against the ends of the container, and 

 by this means the parts that ordinarily would have 

 to bear the maximum stress will have part of this 

 stress transferred to other parts not so heavily 

 stressed, and, consequently, the maximum pressure in 

 NO. 2625, VOL. 104] 



the container can by this means be raised consider- 

 ably, perhaps to 450 tons per square inch. 



In carrying out experiments on larger samples of 

 material and in applying electrical heating to the 

 charge, the container becomes too large to permit of 

 its being made of hardened steel ; therefore, nickel- 



"hin presspahn 

 insuIation 



4 



I 



vuLCxNizco nsRE RiNa 



Fig. 1. — Chiefly for liquids. 



steel is used, as for the barrels of guns. It is heat- 

 treated by quenching in oil from a high temperature 

 after rough machining. Containers (Figs, i and 2) 

 with the thickness of wall equal to the diameter of 

 the bore will stand an internal pressure of 40 tons 

 per square inch repeated almost indefinitely without 

 serious enlargement of the bore, but 100 tons neces- 



ASBESTOS 

 5 MICA LINCR 



PRESSPAHN 

 IN&ULATON ■ 



vulcanized 

 Fibre ring 



Fig 2.— For melting carbon. 



sitates reboring and the fitting of new packing to 

 the ram after each experiment. 



Fig. I shows the arrangement for electrically heat- 

 ing conductors immersed in fluids under high pres- 

 sure. The packing of the ram is a cup leather- 

 backed by a cup of brass; the leather first takes the 

 pressure, and the lip of the brass cup is thereby 



