Voltameter, silver

Coulometer — (previously coulombmeter, or also voltameter) A coulometer is an instrument to measure charge, i.e., to perform -> coulometry. Richards and Heimrod [i] suggested in 1902 the name coulometer to replace the previously used term voltameter . Modern coulometers perform electronic integration of - current over time. However, the first coulometers utilized - Faraday s law, e.g., by weighing the amount of silver that has been deposited on a silver electrode in a silver electrolyte solution the charge could be calculated (silver... 

Rosa, E. B., Vinal, G. W. (1917) The silver voltameter as an international standard for the measurement of electric current. Proc. Natl Acad. Sci. USA. 3, 59-64... 

The amount, or quantity, of electricity passing through a circuit is measured in coulombs, which are, in turn, the product of the amperes and time in seconds.2 At an international electrical conference in London (1908) the ampere was adopted as one of the fundamental units. The ampere is defined as the steady current which, when passed through a solution of silver nitrate in water, under definite conditions to be described later, deposits silver at the rate of 0.00111800 gram per second. This value of the ampere is one-tenth of the c.g.s. (electromagnetic) unit within a few parts in one hundred thousand. The instrument used for measuring current in terms of deposited silver is called a silver coulometer or a silver voltameter.8... 

Reference may also be made here to the new measurements of specific heat by means of the vacuum calorimeter, to which we have already alluded on page 233. The authors mentioned made use of an apparatus which was essentially the same as that described by Schwers and myself the temperature was measured by means of a platinum wire, through which passed an extremely constant current, so that the resistance could be measured by the potential drop, using a potentiometer. During the heating a silver voltameter was included in the circuit as a control on the measurement of time convenient though this is, I think that as a rule the determination of the duration of the heating current can be made with sufficient accuracy to allow the somewhat troublesome silver estimation to be avoided. 

Hittorf calls n and i-n the transport numbers (Zahlen fiir die Uberfiihrung) of the ions. He determined them using different types of apparatus, measuring the electricity transported by having a silver voltameter in the circuit, and analysing the solution around an electrode chemically. For copper sulphate solution the transport number of the copper was 0 285. Hittorf refers to Daniell and Miller with appreciation. His first apparatus, based on theirs, was rather complicated. He showed that the transport number is not affected by the current strength and not much by small changes of temperature with copper sulphate and silver nitrate it depends on the concentration, but appreciably only in concentrated solutions of silver nitrate (for which it was... 

In calculating the change in composition of the anode solution, it must be remembered that an amount of zinc equivalent to the copper deposited in the voltameter has passed into solution. The solution, therefore, contains zinc chloride and sodium chloride. To obtain the weight of water contained in a given weight of the solution, the amounts of these salts must be calculated and subtracted from the weight of the solution. The calculation of the transport number is then carried out in a manner analogous to that employed in the case of silver nitrate. 

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