()14 BUNSEN MEMORIAL LECTURE. 



several. Thus, while eudiometric analysis can not decide whether the 

 gas evolved 1)V the* action of caustic alkali on an acetate is methan(> or 

 a mixture of Cijual volumes of ethane and hydrooen, this can readily 

 be accomplished I)}' absorptiometric methods. 



In the fifth part of the volume he discusses the phenomena of g-as- 

 eous diffusion, and. although admitting the truth of Graham's law for 

 cases of pure diffusion, he obtained results, when a stucco diaphragm 

 of considerable thickness is used, which are not in accord with this 

 law, the conclusion being that the pores of gypsum act upon gases, 

 not as a series of fine openings, but rather as a series of capillary 

 tubes, th(^ phenomena being thus modified 1)V those of trans])irjition. 

 At the end of this ciiaptcr he describes the details of a method for 

 ascertaining, by diffusion, whether a given gas is a mixture or not. 



The sixth and last section relates to the com))ustion ])hen(>mena of 

 gases. The temperature of combustion — that is, the temperature of 

 the interior of a mixture of burning gases — can be calculated from the 

 heat of combustion of the gaseous mixture and the specific heats of 

 the products of combustion under the assumption that the combustion 

 at this high temperature is perfect. This condition, however, is not 

 fulfilled, and Hunsen therefore endeavored to determine this tcMupera- 

 ture by another means, namely, by measuring the pressure produced 

 at the moment of explosion of an inclosed gaseous mixture. 



For this purpose he constructed a wonderfully simple appai-atus, 

 by means of which he ascertained that the maximum tempei'ature of 

 combustion of carbon monoxide and of hydi'ogeii with the theoretical 

 volume of oxygen was, respectively, 3,033"^ and 2,844°. He likewise 

 attempted to determine the rate at which the explosion is propagated, 

 and came to the conclusion that for hydrogen and oxygen this was 

 34 meters per second. Subsequent experiments, especially those of 

 Dixon (Phil. Trans.. 1893 (184), 07), have shown that this rate referred 

 only to the initial period of the coml)ination before the explosion 

 wave had attained its maximum velocity, this latter amounting in the 

 case of h^'drogen and oxygen to the high number of nearly 3,000 

 meters per second, the rate in other gases being of the same order in 

 magnitude, and the ignition appearing to be propagated in somewhat 

 the same manner as a sound wave. 



One of the ])est known of Bunsen's discoveries is that of the carbon- 

 zinc battery, which bears his name. 



The construction of this battery in 1841 (Annalen, 1841 (38), 311) 

 marks an era in the economic production of electricit}'. By the 

 replacement of carbon for the platinum plates of Grove, Bunsen not 

 only greatly reduced the initial cost, but increased the length of 

 time during which the current can be maintained at its maximum. 

 The success of the invention depends upon a method he devised for 

 overcoming the disintegrating action on the carbon of concentrated 



