4 PETAVEL, Compression of Gases by Hydraulic Apparatus 



Where exceptional purity is of no great importance, 

 the compressed gas for this purpose may be obtained 

 commercially. 



For all ordinary work a hand pump will be found 

 sufficient, and, the contents of the receiver being com- 

 pressed at a slow and uniform rate, no special provision 

 is necessary for cooling the gas. 



With regard to the question of safety, it is hardly 

 necessary to point out the importance of securing the 

 best materials and workmanship. Before use the 

 apparatus should be carefully inspected and also tested 

 hydraulically to double the working pressure. 



