Physical Laboratory Course (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1901 Excerpt: ... throws. 65. THE CHEMICAL EFFICIENCY OF THE GRENET CELL. The useful consumption of zinc in a voltaic cell is equal to the amount of zinc which would be deposited by the current delivered by the cell during the time that the cell is in operation. THERMOELECTRIC STUDY. I I The chemical efficiency of the cell is the ratio of useful zinc consumption to total zinc consumption. The total zinc consumption may be determined by weighing the zinc before and after using the cell. The useful zinc consumption may be determined by calculation from the observed average current delivered by the cell, the time, and the electrochemical equivalent of zinc. If it is not convenient to use an ammeter, a copper voltameter may be used and the useful consumption of zinc calculated from the weight of copper that is deposited by the current delivered by the cell. Procedure.--Set up the Grenet cell. Amalgamate the zinc by dipping it in dilute sulphuric acid and rubbing a little mercury over it. Then dry the zinc and weigh it. Do not lower the zinc into the solution until the circuit is all connected. Set up a copper voltameter. Clean the detachable cathode (gain plate) with fine sandpaper, wash, dry, and weigh-it. Then put the cathode in place in the voltameter, fill the voltameter to the neck of the cathode with stock solution of copper sulphate, and lower the battery zinc into its solution, noting the clock reading of this last operation. Allow the cell to furnish current for half an hour and note clock reading when zinc is lifted out of its solution. Remove the zinc and the voltameter cathode, wash and dry each carefully, and weigh. Remark.--The time operations above specified are to enable the average value of the current to be calculated so that the conditions under which the Gre...