that a solid is less compressible than a liquid, its lifting power does not 

 decrease with the depth of immersion, as is the case with light liquids : 

 on the contrary, at a depth, it would increase. One coukl contemplate 

 the use of lithium or paraffin wax. Lithium would certainly be ideal. 

 35*3 cu. ft. (a cubic metre) weighs 121 1 lb. (its specific gravity is only 

 0-55). In fresh water, 35-3 cu. ft. of lithium would suffice to carry 

 a weight of 992 lb. Unfortunately the production of this metal is very 

 limited. Before the last war, when I tried to procure some, one manu- 

 facturer offered me j oz. and another f oz ! Since then the production 

 of lithium has increased in the United States, but it is reserved for 

 researches in nuclear physics. 



In the end, the only solid which one could use was paraffin wax. 

 Its specific gravity is 0-9. In fresh water 35-3 cu. ft. of paraffin would 

 lift only a weight of 220 lb. and in sea water 264 to 287 lb. The 

 bathyscaphe would thus require a very voluminous float : its cost and 

 the difficulties of transport would be considerable. 



Hence we must give up solids and look for a suitable liquid. 



Petrol, a liquid of low specific gravity, fulfils the required con- 

 ditions. But what quality of petrol should be chosen ^ The lighter it is, 

 the more the size of the float can be reduced : but on the other hand, it 

 must not be too light, or it will be too volatile and too compressible. 

 The homogeneity of this petrol must be such that a partial evaporation 

 would not too much modify the density. After studying the problem, 

 the Esso Company furnished us (for the Trieste) with a quality which 

 gave entire satisfaction. It boils at between 140° F. and 176° F., which 

 proves a good homogeneity. At 32° F. its specific gravity is from o-68o 

 to 0-695 : at this temperature 35-3 cu. ft. of this petrol carries on the 

 surface in sea water a load of from 716 to 769 lb. 



To an extent less than gases, but more than solids and water, the 

 volume of petrol is a function of temperature and pressure. That is 

 also a fact that must be taken into account when the problem is to 

 build a bathyscaphe, by arranging, at the bottom of the float, a passage 

 which allows the sea water to enter and to leave freely to compensate 

 these variations: in this way the same pressure will always prevail 

 inside and outside the float, which will allow the float to be built of 

 relatively light metal sheeting. Let us here note the analogy with the 

 small envelope of dirigible balloons. 



The reader will perhaps wonder how we set about finding out how 

 the volume of the petrol varied under the effects of compression and 



[30] 



