392 RECENT PROGRESS IN PHYSICS. 



which both escape as gases at the -f- pole, while the equivalent of 

 hydrogen corresponding to the oxidizing oxygen at the positive pole 

 is evolved at the — pole. If we consider the pure acetic acid to he 

 combined with 1 equiv. of water, the^ process is simply explained by 

 the electrolysis of the equivalent of water, and the oxidation of the 

 acid resulting therefrom in the following manner: 



C H , 2 vol. 



H0+ (aHg) 0^03=^0, Hg 2 vol. 



(2CO2 4 vol. 



The examination of the gasses evolved shows, how'ever, that, in pro- 

 portion to the methyl, more hydrogen and carbonic acid are contained 

 in the gaseous mixture. But this discrepancy is also easily explained. 

 The process would be as indicated in the above equation if only one 

 equivalent of water was electrolized ; but the electrolysis also extends 

 to another part of the water of the solution, and thereby, on the one 

 hand, the quantity of hydrogen is increased, and on the other, a part 

 of the methyl is oxidized to carbonic acid and water, and in this way 

 a greater proportion of carbonic acid is produced. Besides the methyl 

 always contains a small quantity of oxide of methyl. 



§ 181. Electrotype. — After de la Kive already in September, 1836, 

 (Philos. Magazine, Dingier, Poly. Jour., 105 vol.) had directed atten- 

 tion to the fact, that in a Daniell's battery the precipitated copper can be 

 scaled off from that of the battery, presenting a microscopically accurate 

 copy of its surface, it occurred to Jacobi and Spencer, almost simul- 

 taneously as it seems, to make a practical application of this fact. In 

 this they were decidedly successful, as is generally known. 



Jacobi first made, in 1839, a Daniell's battery, in which an engraved 

 copper-plate was employed, but he also made at the same time, experi- 

 ments in a separate decomposing cell, where another copper-plate was 

 placed as the anode opposite to the engraved plate, and thus he kept 

 the solution of the sulphate of copper always saturated.* He also 

 soon found out that an acidulated solution of sulphate of copper is 

 more effective, and that the copper precipitated is pulverulent when 

 the current is two powerful ; he observed that generally not more than 

 fifty to sixty grains of copper per square inch can be reduced during 

 twenty-four hours, when it is required to be compact. In order to de- 

 . termine more exactly the force of current he used a common compass. 

 Jacobi soon after published a memoir on this subject, entitled '^Die 

 Gcdva7ioplastik," Petersburg, 1840. Spencer's experiments (Din- 

 gler's Journal, 75 vol., 1840, and Mechanics' Magazine, No. 846) 

 were, according to him, commenced as far back as 1837; he did not 

 use a separate decomposing cell, but a Daniell's battery, like Jacobi's, 

 with a diaphragm of plaster of Paris, (instead of which unglazed 

 earthenware may also be used,) and common salt with the zinc. The 

 diaphragm was placed vertically in a trough of corresponding dimen- 

 sions and thus formed the two cells. That the zinc ought not to be 

 amalgamated, and that its thickness should be in a certain, but not 



<* The pliencmcnon mentioned in § 176, that the copper does not pass to the negative 

 pole, has here no disturbing iniiuence since the distance of the plates is always veiy small, 

 and the ancde is usually placed above the kathode. 



