1892.] Relative Densities of Hydrogen and Oxygen. 453 



at a tap which for distinctness may be called the regulator. In the 

 generator and in the furnace tubes the pressure must be nearly atmo- 

 spheric, but in the globe there is (at the commencement) a vacuum. 

 The transition from the one pressure to the other takes place at the 

 regulator, which must be so adjusted that the flow through it is 

 approximately equal to the production of gas. At first the manipula- 

 tion of the regulator was a source of trouble and required almost con- 

 stant attention, but a very simple addition gave the desired control. 

 This was merely a long wooden arm, attached to the plug, which 

 served both as a lever and as an indicator. Underneath the pointed 

 extremity was a small table to which its motions could be referred. 

 During the first two-thirds of a filling very little readjustment was 

 needed, and the apparatus could be left for half an hour with but 

 little fear of displacing too much the liquid in the generator. Towards 

 the close, as the motive force fell off, the tap required to be opened 

 more widely. Sometimes the recovery of level could be more con- 

 veniently effected by insertion of resistance into the electric circuit, 

 or by interrupting it altogether for a few minutes. Into details of 

 this kind it is hardly necessary to go further. 



From the regulator the gas passed to the desiccating tubes. The 

 first of these was charged with fragments of solid potash, and the 

 second with a long length of phosphoric anhydride. Finally, a tube 

 stuffed with glass wool intercepted any suspended matter that might 

 have been carried forward. 



The connexion of the globe with the generator, with the Toppler, 

 and with the blow-off, is shown in the accompanying fig. 2. On the 

 morning of a projected filling the vacuous globe would be connected 

 with the free end of the stout-walled india-rubber tube, and secured 

 by binding wire. The generator being cut off, a high vacuum would 

 be made up to the tap of the globe. After a couple of hours' stand- 

 ing the leakage through the india-rubber and at the joints coold be 

 measured. The amount of the leakage found in the first two hours 

 was usually negligible, considered as an addition to a globeful of 

 hydrogen, and the leakage that would occur in the hours following 

 would (in the absence of accidents) be still smaller. If the test were 

 satisfactory, the filling would proceed as follows : 



The electric current through the generator being established and 

 the furnace being heated, any oxygen that might have percolated into 

 the drying tubes had first to be washed out. In order to do this 

 more effectively, a moderate vacuum (of pressure equal to about 1 inch 

 of mercury) was maintained in the tubes and up to the regulator by 

 the action of the pump. In this way the current of gas is made very 

 rapid, and the half hour allowed must have been more than sufficient 

 for the purpose. The generator was then temporarily cut off, and a 

 high vacuum produced in the globe connexion and in the blow-off 



