Electrical measurementsA laboratory manual . superior in some respects, isa flat silver plate, moiuited between two anode plates ofpure silver, as shown in Fig. 77. The plates are mounted on a hard-rubberA ,.B strip A by means of stiff spring loosening thescrew B^ the platescan all be removedtogether from the so-lution. The platescan be raised or low^-ered by means ofa rack and is a convenientmethod of effectinga fine adjustmentof the resistance ofthe circuit in mak-ing and maintaining an electrical balance. The anodeplates do not need to be covered with filter paper, sinc
Electrical measurementsA laboratory manual . superior in some respects, isa flat silver plate, moiuited between two anode plates ofpure silver, as shown in Fig. 77. The plates are mounted on a hard-rubberA ,.B strip A by means of stiff spring loosening thescrew B^ the platescan all be removedtogether from the so-lution. The platescan be raised or low^-ered by means ofa rack and is a convenientmethod of effectinga fine adjustmentof the resistance ofthe circuit in mak-ing and maintaining an electrical balance. The anodeplates do not need to be covered with filter paper, sinceany dislodged particles will fall to the bottom of the care is necessary in washing, drying, and Aveigh-ing the gain plate. It may be handled and weighed bymeans of a hook of stiff brass wire for suspension. Thisis a better plan than to run the risk of detaching parti-cles of silver by laying the plate down, except in thebottom of a glass tray in washing. This form of voltam-eter provides better insulation than those in which the. Fig. 77. MEASUREMENT OF CUREENT. 161 bowl rests on a base on which the nitrate of silver solu-tion is almost certain to be spilled by .ack of extremecare. In this form neither the base n-oi- the standardforms any part of the conducting circuit. 79. The Copper Voltameter. — When large currentsare measured by electrolysis. the copper voltameter isemployed instead of the corresponding one of silver,because the size of the plates required would make thelatter too expensive. The copper voltameter scarcelyequals the silver voltameter in accuracy, partly becauseof oxidation and partly because the electrochemicalequivalent of copper is much smaller than that of silver,so that for a given current the quantity of copper depos-ited is less than that of silver, and it cannot be weighedwith so small a percentage of error. On the other hand,the copper has the advantage of simplicity in manipu-lation. Silver is always deposited in a crystalline form,and
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Keywords: ., bookcentury1800, bookdecade1890, bookpublisherbosto, bookyear1895
