HISTOKY, &c., OF INDUCTION INSTRUMENTS. 315 



over which a little water is poured, and the zinc covering all. (It 

 will be remembered that, before the employment of bisulphate of 

 mercury, the elements were arranged in the same manner, and 

 that, instead of the solution of bisulphate of mercury, I employed, 

 originally, nitric acid, and subsequently diluted sulphuric acid, 

 with which to saturate my carbon.) But the mode of preparation 

 of their batteries does not appear to me to give results equally 

 advantageous with mine. 



The powder of bisulphate of mercury, that I strew upon the 

 surface of my carbon plate, is sufficient in quantity to form, when 

 moistened, a stratum half a millimetre in thickness. The water 

 which I pour upon this paste, when I am about to use it, saturates 

 it completely ; and the thick cloth, which is placed between it and 

 the zinc itself, is well soaked with water. Thus charged, my battery 

 will continue in action for twelve hours, with rapid intermissions ; 

 and for several days, with the slow intermissions that I habitually 

 employ. In the intervals between the applications, the zinc only 

 is removed and wiped (so that its bright surface is always amalga- 

 mated) ; and, in order to avoid the evaporation of liquid by contact 

 with the air, a plate of hard caoutchouc replaces the zinc. 



With this mode of preparation, a battery is for a long time 

 always ready for action before I am called upon to renew the 

 bisulphate of mercury ; it preserves its force until the entire 

 decomposition of the salt ; and there is only occasion to pour, from 

 time to time, a little water upon the cloth. 



The bisulphate of mercury batteries, in the small instruments of 

 Gaiffe, Euhmkorff, and Trouve, contain only the small quantity 

 of bisulphate which they can hold in solution ; so that they cannot 

 be used for more than an hour at a time, without recharging the 

 battery. After using them only for a few minutes, it is necessary 

 each time to throw away the liquid, to clean the zinc, and to 

 renew the preparation for the next patient. 



Lastly, 1 have observed that my battery polarizes less, which 

 I attribute to the application, immediately against the zinc, 

 of the wet cloth, which forbids a great number of the bubbles of 

 hydrogen gas produced by the action of the battery to adhere to 

 its surface. In other batteries there is nothing to prevent these 

 bubbles of hydrogen from sticking to the zinc, and shielding the 

 greater part of its surface from the chemical action of the battery. 

 I therefore advise makers who employ -flat and unclosed batteries 

 of bisulphate of mercury, to prepare them like mine. 



The flash hatter ij ofhisulj^hate of mercury, which M. Ruhmkorft 

 has added to his hospital induction apparatus (see fig. 79, page 

 297) is well conceived. 



