316 LOCALIZED ELECTRIZATION. 



It recalls, indeed, by its form, its disposition, and its meclianisin, 

 the flask battery of M. Grenet, from \\liicli it differs by the employ- 

 ment of a saturated solution of bisulphate of mercury, in place of 

 chromate of potash, and by being mounted in hard caoutchouc, 

 instead of in metal, which inevitably undergoes amalgamation by 

 the mercury, and becomes brittle. 



This flask battery of M. Ruhmkorff will w'ork for a long time 

 without requiring to be recharged. When not in use, the zinc is 

 drawn up out of the solution of bisulphate of mercury, by means 

 of a metallic stem; and when it is required, it is pushed down 

 again into the liquid. This may be done gradually, in such a way 

 as to increase by degrees, and at pleasure, the intensity of the 

 current. The employment of this battery will be a source of great 

 economy in hospitals, because it occasions no damage to iustru- 

 ments, and because its management is so simple. 



But the flask of this battery is itself seven or eight centimetres 

 in height, without reckoning six centimetres, or more, for the stem, 

 which, when it is not in use, serves to keep the zinc raised out of 

 the solution. In other words, its size fills a considerable space 

 in the apparatus, and its height prevents it from being enclosed in 

 the same box. This is the only fault which can be found with it ; 

 but its bulk is unquestionably a real inconvenience, and renders 

 the apparatus less portable. 



Other manufacturers, endeavouring, like M. Euhmkorff, to 

 render the manipulations of the batteries more easy and less 

 frequent, have particularly applied themselves to diminish their 

 bulk, and to make them more portable. They have enclosed them 

 in a box of hard caoutchouc, by the aid of a screwed lid, to which 

 the solid parts of the battery are fixed. These small hermetically- 

 closed batteries were at first emj^loyed as sourc^es of amusement, 

 on account of their small bulk. Conjurors carried them in their 

 pockets, and, conveying them adroitly into their hands, set in action 

 from a distance, the electro-magnets which communicated with 

 them. Notwithstanding the trivial origin of these little batteries, 

 their application, as medical induction instruments, has neverthe- 

 less been highly useful. 



It is, however, just to say that M. Trouve appears to have been 

 the first to construct a battery in a closed caoutchouc box, which he 

 called an hermetic battery, and which has already been described. 



M. Gaiffe has given to his batteries the same external form as 

 those of M. Trouve. But their composition is essentially different, 

 since they consist of chloride of silver (see figs. 87 and 88). M. 

 Trouve's bisulphate of mercury hermetic battery will only work for 

 an hour and a half, after which it requires to be recharged. The 



