6 M. H. Her wig on the Disintegration of the 



cock G. One of the tubes, A, is furnished with two platinum 

 electrodes ; the other, B, has but one. But delivery-tubes (not 

 shown in the drawing) of the usual form fit upon the tubes above 

 the stopcocks F, F. When about to be used, all the stopcocks 

 are opened and diluted sulphuric acid poured in through the re- 

 servoir until it has eliminated all air and is running out itself 

 at the delivery-tubes. The stopcock G is now shut and the bat- 

 tery connected, as circumstances may require, either with the 

 two electrodes in A, or with one in A and one in B. Gas is 

 allowed to escape freely until all dissolved air is eliminated. 

 The stopcocks F F are then closed, G opened, and the liquid 

 in A and B allowed to sink until it just covers the electrodes. 

 G is then closed, and F F opened, when the gases may be intro- 

 duced into the eudiometer in the ordinary way, or into the above- 

 described apparatus in the way there indicated. Connexion be- 

 tween the gas-generator, the tubes A and B, and the reservoir 

 E being shut off by the stopcock G, there is never any difficulty 

 in forcing the gas through the mercury into the eudiometer. 



The whole apparatus is attached to a mahogany board, H, 

 which fits into the box K, shown cut through the middle in the 

 drawing, either as represented, when in use, or, when not in use, 

 as a lid, with the apparatus attached to its inner side. The box 

 thus fulfils the double purpose of a convenient stand and a safe 

 packing-case. The only alteration which I should be inclined 

 to make, would be to have the lid to which the apparatus is 

 attached made of vulcanite, to avoid the risk of the wood's warp- 

 ing in damp weather. 



II. On the Disintegration of the Electrodes in the Galvanic Arc 

 of Light. By Hermann Herwig*. 



THE quantities of substance which are thrown off in fine 

 powder from the electrodes of the voltaic arc have hitherto 

 been determined only very uncertainly. To the statements here- 

 upon, made chiefly by Van Breda f and Matteucci^ a reduction 

 to an otherwise well-known action of the current, perhaps to a 

 simultaneous voltametric action of it, is wanting ; and, besides, 

 the experiments were made under circumstances which quantita- 

 tively can present only an indistinct picture of the disintegration, 

 as will be seen from the following. Only a series of experiments 

 by Grove § on the present subject appears to wear a more precise 



* Translated from a separate impression, communicated by the Author, 

 from Poggendorff's Annalen, vol. cxlix. pp. 521-533. 



t Pogg. Ann. vol. lxx. p. 326. 



\ Comptes Rendus, vol. xxx. p. 201 ; Ann. de Chim. et de Pkys. S. 3. 

 vol. xxxii. p. 350. 



§ Phil. Mag. S. 3. vol. xvi. p. 4/8. 



