BUNSEN MEMORIAL LECTURE. 615 



nitric acid. This he effected by strongly igniting the cylinders, thus 

 foreshadowing the process adopted on a large scale for oTaphitizhur 

 the carbon poles now so generally used for electro-industrial pui-pose^ 

 by Ignition in the electric furnace. It is interesting to remember that 

 it was Bunsen who, so early as 1843, pointed out that the electric cur- 

 rent could be made use of as a means of illumination. He descrilx-s 

 how, by using a battery of 44 of his elements, a light equal in illumi- 

 nating power to 1,171.3 candles can be obtained for an cxpcndituiv of 

 1 pound of zinc per hour, and giving a light -'the brilliancy of which 

 the eye can scarcely support." He adds that by inclosing the carbon 

 poles in a globe of glass the wear of carbons by oxidation might be 

 minimized. In short, he describes the tirst step towaixl the modern 

 system of arc lighting rendered generally applicable on the large scale 

 by the discovery of the dynamo. In his tirst connnunication respect- 

 ing this battery Bunsen gave a careful estimate of the work it can 

 accomplish. He showed that three cells will, in thirty minutes, decom- 

 pose 0.6775 gram of water, yielding 1,137 cubic centimeters of mixed 

 gas, measured at 0° and 760 millimeters. The corresponding loss of 

 zinc in each cell was then determined, the result showing that the 

 same weight was dissolved in each, and that the weights thus found 

 correspond closely with the zinc equivalent for the above amoiuit of 

 water decomposed. A few years later, in 1S4S, he determined the 

 electro-chemical equivalents for zinc and water. For the tirst of these 

 he obtained the value 0.033, and for the latter 0.001>27; in other words, 

 in order to decompose 1 milligram of water per second a cui'rent of the 

 absolute intensity of 106.33 is necessary. These experiments confirm 

 Faraday's law, showing that the quantity of water decomposed is pro- 

 portional to the quantity of circulating electricity, and that the nature 

 of the poles, as well as the conducting power of the li(|uids decoini)osed, 

 exerts no influence on the result. 



We owe to Wilhelm Weber the first determination of the scientific 

 units for electrical measurements, and in 1840 he ol)tained the mnnber 

 0.009376 for the electro-chemical equivalent of watei- with his unit 

 current. The difliculties which surround the sul)ject are: (1) The 

 measurement of the current, and (::i) the al)sorption of the decomposed 

 gases by water and electrodes, and (3) the production of ozone. Bun- 

 sen improved the voltameter by evolving the mixed gases from hot 

 aciditied water, by which the second and third of these diflieulti(>s were 

 overcome. At present voltameters depositing copper or silver are 

 employed, and the ampere, which is now our practical unit, is one- 

 tenth of that used by Wel)er and Bunsen. so that the electro-.-h.Mnu-al 

 equivalent of water is 0.0009315 gram, meaning that 1 ump.Te decom- 

 poses that amount of water in one second. 



This, however, was only the b,>gi,n.ing <.f the work >vhi.h the Wnu- 

 sen battery was destined to perform. It was not untu 18^2, when m 



