I02 



NA TURE 



[June 2, 1892 



with its accompanying contamination. Moreover, the 

 supply of acid that can be included in one charge of the 

 generator is inadequate, and good results are only ob- 

 tained as the charge is becoming exhausted. These diffi- 

 culties are avoided when zinc is discarded. The only 

 material consumed during the experiments is then the 

 water, of which a large quantity can be included from the 

 first. On the other hand, the hydrogen liberated is 

 necessarily contaminated with oxygen, and this must be 

 removed by copper contained in a red-hot tube. In the 

 experiments to be described the generator was charged 

 with potash,^ and the gases were liberated at platinum 

 electrodes. In the case of a hydrogen filling, the oxygen 

 blew off on one side from a mercury seal, and on the 

 other the hydrogen was conveyed through hot tubes con- 

 taining copper. The bulk of the aqueous vapour was de- 

 posited in a small fiask containing strong solution of 

 potash, and the gas then passed over solid potash to a 

 long tube packed with phosphoric anhydride. Of this 

 only a very short length showed signs of being affected 

 at the close of all operations. 



With respect to impurities, other than oxygen and 

 oxides of hydrogen, which may contaminate the gas, we 

 have the following alternative. Either the impurity is 

 evolved much more rapidly than in proportion to the 

 consumption of water in the generator, or it is not. If 

 the rate of evolution of the impurity, reckoned as a frac- 

 tion of the quantity originally present, is not much more 

 rapid than the correspondingly reckoned consumption of 

 water, the presence of the impurity will be of little import- 

 ance. If, on the other hand, as is probable, the rate of 

 evolution is much more rapid than the consumption of 

 water, the impurity is soon eliminated from the residue, 

 and the gas subsequently generated becomes practically 

 pure. A similar argument holds good if the source of the 

 impurity be in the copper, or even in the phosphoric 

 anhydride ; and it applies with increased force when at 

 the close of one set of operations the generator is re- j 

 plenished by the mere addition of water. It is, however, 

 here assumed that the apparatus itself is perfectly tight. 



Except for the reversal of the electric current, the 

 action of the apparatus is almost the same whether oxy- 

 gen or hydrogen is to be collected. In the latter case 

 the copper in the hot tubes is in the reduced, and in the 

 former case in the oxidized, state. For the sake of dis- 

 tinctness we will suppose that the globe is to be filled 

 with hydrogen. 



The generator itself is of the U-form, with unusually 

 long branches, and it is supplied from Grove cells with 

 about 3 amperes of electric current. Since on one side 

 the oxygen blows off into the air, the pressure in the 

 generator is always nearly atmospheric. Some trouble 

 has been caused by leakage between the platinum elec- 

 trodes and the glass. In the later experiments to be here 

 recorded these joints were drowned with mercury. On 

 leaving the generator the hydrogen traverses a red-hot 

 tube of hard glass charged with copper,^ then a flask con- 

 taining a strong solution of potash, and afterwards a 

 second similar hot tube. The additional tube was intro- 

 duced with the idea that the action of the hot copper in 

 promoting the union of the hydrogen with its oxygen 

 contamination might be more complete after removal of 

 the greater part of the oxygen,Jwhether in the combined or 

 in the uncombined state. From this point onward the gas 

 was nearly dry. In the earlier experiments the junctions 

 of the hard furnace tubes with the soft glass of the 

 remainder of the apparatus were effected by fusion. 

 One of these joints remained in use, but the others 

 were replaced by india-rubber connexions drowned in 



' At the suggestion of Prof. Morley, the solution was freed from car- 

 bonate or nearly so, by the use of baryta, of which it contained a slight 

 excess. 



'f The copper must be free from sulphur; otheiv 

 with sulphuretted hydrogen is somewhat persistent. 



NO, 1 1 79, VOL. 46] 



mercury. It is believed that no leakage occurred at 

 these joints ; but as an additional security a tap was 

 provided between the generator and the furnace, and was 

 kept closed whenever there was no forward current of 

 hydrogen. In this way the liquid in the generator would 

 be protected from any possible infiltration of nitrogen. 

 Any that might find its way into the furnace tubes could 

 easily be removed before the commencement of a filling. 

 Almost immediately upon leaving the furnace tubes 

 the gas arrives at a tap which for distinctness may be 

 called the regulator. In the generator and in the 

 furnace tubes the pressure must be nearly atmospheric, 

 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 manipulation of 

 the regulator was a source of trouble, and required almost 

 constant 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 filhng 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. Some- 

 times the recovery of level could be more conveniently 

 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 connection of the globe with the generator, with 

 the Toppler, and with the blow-off, is shown in the 

 accompanying figure. On the morning of a projected 



TO OENBRATOR. 



contammation 



filling the vacuous globe would be connected with the 

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

 secured by winding wire. The generator being cut off, a 

 high vacuum would be made up to the tap of the globe. 



