Chemistry and Physics. 411 



action of light and actinism — the first being necessary to effect the 

 secretion of the carbon and the latter for the oxydation of this deposit- 



ed carbon. 



if Photography to copying M 



jects; by Dr. Carpenter, (Rep. Brit. Assoc, for 1847, Athen., No. 

 1028.)— Numerous specimens of Daguerreotype and other photo- 

 graphic copies of very delicate microscopic objects were exhibited. 

 These were peculiarly beautiful, and were obtained by the use of the 

 solar microscope, the object being thrown upon the paper or plate 

 instead of upon the ordinary screen. The minute fidelity of these 

 copies was far beyond anything which could be obtained by the artist ; 

 and the ease with which "they were produced, particularly on photo- 

 graphic paper, recommended this application of the art to the attention 



of naturalists. 



7. On the Quantity of Electrolysis as affected by the Extent of the 

 Sectional Area of the Electrolyte; by W. R. Grove, Esq., (Proc. 

 Brit. Assoc, for 1847, Athen., No. 1028.)— The experiments here de- 

 scribed were made two years ago, and were intended as the commence- 

 ment of a series of researches on the influence of quantity in voltaic ar- 

 rangements, both as regarded the generating and also the conducting 

 portions of the circuit. A single cell of a zinc and platina diaphragm 

 battery charged on the negative side with peroxyd of manganese and 

 hydrochloric'acid, has a more intense action and will decompose more 

 water in a given time than a similar battery charged with nitric acid ; 

 but two or more cells of the former, arranged in series, are far inferior 

 to a similar number of the latter, particularly if large electrodes be em- 

 ployed. This inferiority in the chlorine battery arises, I believe, from 

 want of quantity in the electro-negative element : the chlorine is slowly 

 liberated and much diluted by the liquid hydrochloric acid, while the 

 nitric acid supplies an indefinite quantity of what we may term liquid 

 oxygen. Thus the cathode is in the one case bathed by hydrochloric 

 acid, and in contact with a comparatively small portion of chlorine, 

 while in the other case it is covered to nearly its whole extent by oxy- 

 gen ; in other words, the sectional area of the efficient electrolyte is 

 smaller in the first case than in the second. It is admitted that in me- 

 tallic conductors the facility of conduction is directly as the sectional 

 area of the conducting substance; but the problem is rendered more 

 complex in electrolytes by the polarization or reaction occasioned by 

 the liberated ions, and also by the quantity of the efficient chemical in- 

 gredients contained in the electrolyte, whether they act dn^Mm 

 or secondarilv by absorbing or preventing the Iteration of the cat hi on s 

 ^ the cathode. Dr. Faradav, in his » Researches,' has shown tha ^sep- 

 arate pairs of electrodes interposed in the same circuit, yield the same 

 amount of gas whatever be their size ; and this result has been m n- 

 terpreted by many, and regarded as establishing that the size or elec- 

 trodes with regard to that of the battery plates makes no P™c >ca oii- 

 ference in the amount of S as liberated. From the g re » l P^ "' ": 

 Perience which the application of voltaic electricity to the electrotype 

 and its kindred arts has promoted, this error has now for some years 

 been removed. I believe I was the first to point out the nece s.ty ■ of 

 electrodes equal in area to the battery plates in order to yield the lull 



