384 MESSRS. V. H. VELEY AND J. J. MANLEY ON 



THE METHOD OP PERFORMING AN EXPERIMENT. 



The electrolytic cell was charged with the required mixture of nitric acid and 

 recently-melted ice as previously described, then placed in the inner chamber of the 

 tank and its electrodes connected up with the bridge leads. When an hour had 

 elapsed after equilibrium of temperature had been first observed, preliminary 

 measurements were made in order to ascertain approximately the conductivity of the 

 acid, and thus not only to facilitate the final measurement, but also to eliminate the 

 risk of decomposition. The cell was then emptied, recharged with a second portion 

 of the acid, and connections made as before ; after an interval of some hours the final 

 measurements were made as follows : 



The graduated glass tube was adjusted so that division 5 of its scale coincided 

 with the point of intersection of the cross threads of the telescope ; the standard 

 coils were placed in the left gap (L) and the electrolytic cell in the right gap (R) of 

 the bridge ; if then the current from the commutator was found satisfactory, 

 connection was made with the bridge and its accessories, and a first balance 

 obtained. 



The current was then switched off, the position of the coils and electrolytic cell 

 interchanged, the current switched on, and a second balance obtained. The movable 

 electrode was then raised to division 15 on the scale, and the value of the standard 

 coils altered so that their combined resistances were approximately equal to those of 

 the introduced length of acid and leads (as determined by the preliminary experiment), 

 while simultaneously the resistances in the control box were also changed so as to 

 maintain the current intensity uniform. Then balancings were obtained with the 

 electrolytic cell successively in the II and L gaps as before. The whole series of 

 operations were repeated for the introduction of the second length of acid caused by 

 raising the graduated glass tube through another five divisions. 



The thermometers in the standard resistance box, bridge and tanks were read 

 before and after each set of observations, and any necessary corrections for alteration 

 of temperature subsequently applied. 



As an illustration, all the measurements and observations for two samples of acid, 

 namely of 1'299 and 30 - 52 per cent, concentration are given ; these particular values 

 have been selected as those of maximum and minimum conductivity for each form of 

 electrolytic cell. 



