HIGH-PRESSURE PHYSICS — BRIDGMAN 



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proportionate share in supporting the pressure. In practice it turns 

 out that the limit for heavy cylinders of the best heat-treated steels 

 is about 15,000 atmospheres; this may be increased for brief operations 

 to 20,000 or more. Still higher pressures can perhaps be achieved 

 by shrinking hoops onto the vessel, as in a well-known method of gun 

 construction, but even with such vessels the upper limit yet reached, 

 in some experiments by Newitt, is in the neighborhood of 30,000 atmos- 

 pheres. While the pressure vessel is reaching its limit the piston also 

 is reaching its limit, the upper limit for the compressive strength of 

 any steel now available being also in the neighborhood of 30,000 

 atmospheres. 



Figure 2. — Simple method of giving external support to a pressure vessel by using the 

 thrust on the piston, which produces internal pressure to push the whole vessel into a 

 supporting conical sleeve. 



To reach higher pressures, a radical change in design is necessary. 

 For the piston, however, it is sufficient to change the material of 

 which it is made to carboloy, which has a compressive strength more 

 than twice that of the best steels. Carboloy is a product of powder 

 metallurgy, and is a sintered aggregate of tungsten carbide cemented 

 with a small amount of cobalt as binder. To obtain greater strength in 

 the pressure vessels more elaborate methods are necessary. In all my 

 experiments it has involved giving the pressure vessel some sort of ex- 

 ternal support to counteract the effect of the internal pressure. The 

 simplest way of doing this is to make the vessel conical on the outside 

 surface and to push the entire pressure vessel into a conical supporting 

 sleeve as internal pressure increases. The vessel may be pushed into its 

 sleeve in various ways. The simplest is to let the thrust that drives 

 the piston drive the vessel also into its sleeve ; a method of doing this 



