MEDICAL BATTEEIES. 55 



ascends with difficulty to the point of contact ; and I have checked 

 endosmosis by dipping the upper end of each carbon in melted 

 wax, which, in cooling, fills the pores into which it has penetrated. 

 For greater firmness, I have covered this upper end with a coat of 

 varnish, except at the points of contact. Lastly, I have platinized 

 the plates of copper at their points of contact. 



(/). Marie-Bavx/s suljohate of had hattery. — The high price of 

 protosulphate of mercury has probably stood in the way of its 

 introduction into common use. This would doubtless be foreseen 

 by the inventor; who has employed himself in endeavours to 

 remove the obstacle. Moreover, the battery leaves us something 

 to desire, as I have said, with regard to the constancy of its 

 action. 



It has occurred to this ingenious physicist : (1) to replace the 

 mercurial paste by a paste made with powdered sulphate of lead 

 and a saturated solution of marine salt ; (2) to substitute for the 

 carbon a thin plate of tinned copper, seven centimetres square, 

 and rolled upon itself; (3) to fill the space between the porous 

 cell and the external vessel with a concentrated solution of 

 marine salt ; (4) to coat with tin the plates of copper that form 

 the connections between the two parts (zinc and lead) of the 

 battery. 



Thus formed, the sulj^hate of lead battery affords a current of 

 the greatest constancy. In a damp place and in an even tem- 

 perature it has been in action for more than a year in my room, 

 requiring no farther care than to replenish the saline solution 

 from time to time, so as to keep it always at nearly the same level. 

 It is much less costly to procure or to maintain than the battery 

 with sulphate of mercury ; and for all these reasons I prefer it to 

 all others for the application of continuous or interrupted voltaic 

 currents. But, as its electro-motor force is less by one-half than 

 that of the sulj)hate of mercury, I have found it necessary to 

 increase the number of the elements in order to meet the demands 

 of practice. Moreover, its bulk is such that it is only applicable 

 in my own house. 



{g). Siemens' hattery (called also Remak's). — Quite recently, a 

 battery, invented by a very distinguished Prussian engineer, M. 

 Siemens, has been much extolled in Germany. It is often called 

 also Eemak's battery ; from his having rendered its use general 

 in medical practice. 



This battery of Siemens' (fig. 14) is no more than a modification 

 of Daniell's, in which the inventor has sought chiefly to increase 

 resistance by placing between the porous cell that contains the 

 sulpliate of copper and the zinc a paste of paper and sawdust 



