384 Intelligence and Miscellaneous Articles. 



ON THE USE OF CUPRIC NITRATE IN THE VOLTAMETER, AND THE 

 ELECTRO-CHEMICAL EQUIVALENT OF COPPER. BY F. E. BEACH. 



According to the author the advantages possessed by the nitrate 

 may be enumerated as follows : — 



1 st. The weight of copper deposited does not appear to depend 

 on the current-density. 



2nd. It permits the use of a high current-density. 



The limit is not easily stated. When 0-25 ampere per square 

 centimetre is reached the cathode needs watching, for it will fringe 

 at the edge but does not become powdery. 



No way was found to prevent the branching with a high current- 

 density.. 



A greater amount of NH 4 C1 should be present when the current- 

 density is increased. 



3rd. The weight of copper is practically independent of the 

 temperature between 10° and 35° 0. 



The tendency to oxidation is increased by lowering the tempera- 

 ture, but this may be easily counteracted by the addition of more 

 JN T H 4 C1. 



4th. The solution may be used a number of times. 



5th. The equivalent agrees to four figures with that calculated 

 from the best chemical determinations, viz. : — 



Eichards Eq. =(3294-4 + 0-1) x 10-7. 



First Series Eq. =(3294-8 + 0-43) x 10-7. 

 Second Series Eq. =(3293-9 + 0-39) x 10-7. 



The purity of the nitrate as a condition of success is to be 

 emphasized. One specimen tried, which contained nitrite, was 

 absolutely worthless with the foregoing treatment. — American 

 Journal of Science, August 1893. 



NOTE BY LORD KELVIN ON ELECTRIC MOLECULES FOR THE 



EXPLANATION OF THE PIEZO -ELECTRIC AND PYRO-ELECTRIC 



PROPERTIES OF CRYSTALS. 



Since my communication of a short article " On a Piezo-electric 

 Pile " to the Philosophical Magazine {supra, p. 342), I have found 

 a very important article* by Messrs. J. and P. Curie, in which 

 precisely the same combination is described, and the application 

 of the principle illustrated by it to explain all the piezo-electric 

 and pyro-electric properties of crystals is pointed out. 



The discovery of the piezo-electric property in crystalline matter 

 has been made known to the world by the experimental researches 

 of the brothers Curie ; and it now interests me exceedingly to find 

 that they have also given what seems to me undoubtedly the true 

 electro-molecular theory of the constitution of crystals, explaining 

 not only piezo-electricity, but the old known pyro-electricity ; and 

 bringing these properties into relation with the electro-chemical 

 constitution of the crystalline molecule. Kelvin". 



Aix-les-Bains, Sept. 21, 1893. 



* Comptes Rendus of the French Academy of Sciences for Feb. 14, 1881. 



