GALVANISM. 



407 



Fig. 



What is the 

 construction of 

 Grove's bat- 

 tery? 



3( the liquid on each side, within its pores, but prevents the solid proaucta 

 of decomposiDDu from passing from one plate to the other. 

 Describe Dan- Daniel's constant battery, constructed according to this 

 iel's constant principle, and represented in Pig. 340, maintams an efiective 



ttery. galvanic action longer 



than any other ; a is a hollow cylinder 

 of copper; z, a solid rod of amalgam- 

 ated zinc; and e, a porous tube of 

 earthenware separating the two. 

 Diluted sulp'auric is placed in the 

 porous tube, and a saturated solution 

 of sulphate of copper in the copper 

 cylinder. 



One of the most eflQ- 

 cient batteries is that 

 kno\vn as Grove's bat- 

 tery, from its mventor, and 13 the form generally used for 

 telegraphing and for otlier purposes in which powerful galvanic action is re- 

 quired. It consists of a plain glass tumbkr, in which is placed a cyhnder of 

 amalgamated zinc, with an opening on one side to allow a free circulation of 

 the liquid Within this cyluider is placed a porous cup, or cell, of earthen- 

 ware, in which is suspended a strip of platinimi fetened to the end of a ztac 

 arm projecting from tlie adjoining zinc cylinder. The porous cup containing 

 the platinum is filled with strong nitric acid, and the outer vessel containing 



the zinc with weak sulphuric 

 Fig. 341. aci(j_ Pig ^^i represents a 



series of these cups, arranged 

 to form & compound circuit, 

 with their terminal poles, P 

 and Z. This form of battery- 

 is objectionable on account 

 of the corrosive character of 

 the acids employed, and 

 the deleterious vapors tliat 

 arise from it when in ac- 

 tion. 



What is the dis- 777. The electricity evolved by a single gal- 

 ter"if*^^T^ic vanic circle is great in quaatity, but weak in 

 electricity? intensity. 



These two qualities may be compared to heat of different temperatures. A 

 gallon of water at a temperature of 100° has a greater quantity of heat than a 

 pmt at 200° ; but the heat of the latter is more intense than that of the former. 



What is the dis- The electricity, on the contrary, produced 



ter"of frSc^'ti'o"^ ^y friction, or that of the electrical machine, 



electricity? jg small iu quautity, but of high tension, o: 

 intensity. 



