684 Prof. J. Joly on the Closure of Small 



The hydraulic press used was a Tangye Press, with Bourdon 

 gauge attached, and capable of affording a crushing for< e of 

 400 tons ; the water being pumped in by hand by two pumps, 

 a fast low-pressure pump and a slow high-pressure pump. 

 The crushing mortar is placed centrally on the platten of the 

 press, and this is up-lifted by the operation of the pumps till 

 the plunger of the mortar comes against the ceiling of the 

 press. Further pumping now forces down the plunger. 



In order to counteract the slow leakage of water around 

 the leather collar of the press, a very simple and effective 

 device was adopted. 



In the cellar beneath the laboratory a steel gas-cylinder of 

 the usual type, filled with compressed air, v as installed. 

 This was supported in an inverted position, i. e. nozzle 

 downwards, and a high-pressure copper pipe brought up 

 from it through the floor and tapped into the high-pressure 

 water-chamber of the press. A screw cone-in-cone stop- 

 cock served to open connexion between the tube and the 

 press. The action was as follows : — When the hydraulic 

 pressure had risen above a certain point, the stopcock was 

 opened and water from the press allowed to flow into the 

 gas-bottle, raising the pressure in the latter. The pumping 

 was then continued till the required pressure was attained. 

 If, now, the whole system was left to itself, any small leakage 

 of water was made good by water fed by air-pressure from 

 the bottle. In short, the air acts as a spring, storing energy 

 and replacing its loss by supplying water practically at the 

 original pressure. This acted very successfully. For months 

 the pressure was maintained constant with no loss detectable 

 by the manometer. The temperature in the cellar was very 

 uniform. 



In two of the experiments the rock hemispheres were 

 used without any cavity being formed in either of the hemi- 

 spheres. A cavity common to hoth was provided by the 

 device of inserting a thin steel washer between the hemi- 

 spheres : this washer having a central circular opening of 

 the same diameter as that of the cavity as formed in the 

 hemisphere. In this case care was taken to grind the washer 

 to a uniform thickness of about \ a millimetre. The washer 

 may be cemented between the hemispheres with hard Canada 

 balsam or used without cement. 



It will be evident that by ordering the experiments as 

 described above, directness and sensitiveness are the objects 

 in view. The sphere is the form of highest symmetry, and 

 the mathematical treatment of stress and strain in the deter- 

 mination of conditions of rupture is simpler than in any other 



