274 Prof. W. Beetz on the Development of 



copper*. In any case, however, the second deflection shows 

 that the black precipitate is negative towards magnesium ; the 

 negative nature vanishes with the black body itself. The entire 

 proceeding is moreover independent of the closing of the secon- 

 dary battery. If the battery-current be broken and connexion 

 with the galvanometer be made only after the lapse of some 

 time, the blackened wire is immediately negative ; if the mag- 

 nesium wires be not connected with the instrument till the black 

 incrustation is gone, scarcely any electrical difference is then 

 observed between them. Similar experiments can also be made 

 with other conducting liquids; the process, however, is more 

 intricate and furnishes no definite results, because hydrate of 

 magnesia may be formed on both wires, which is not possible 

 when dilute acids are employed. 



The first idea which presented itself with regard to the parti- 

 cipation of the suboxide in the development of hydrogen was, 

 that the current only partly decomposed the salts of the solu- 

 tions in the normal manner, and partly the water itself. If, for 

 example, mH were given off from the cathode in a solution of 

 chloride of sodium, and joH from the anode, the quantity of 

 magnesium dissolved is, according to the experiments described, 

 = (m+jo)Mg. Let the current so divide itself that it decom- 

 pose x equivalents of water, then #0 and (m— x)C\ will be set 

 free. The latter combines with (m— a?)Mg, leaving (p + x)Mg, 

 which forms an oxide with ocO. When this compound has been 

 completely oxidized to magnesia, it contains (p + x)M.gO. If 

 we could determine this quantity experimentally, we should also 

 know cc, the portion of the current that decomposes water. I 

 examined therefore, first of all, whether the quantity of magnesia 

 formed in the nascent state, in a salt liquid holding chloride of 

 magnesium in solution, was considerable. 0*067 grm. of mag- 

 nesium wire, equivalent to 63*6 cubic centims. of hydrogen, was 

 placed under a eudiometer in a solution of common salt which 

 had frequently been used for electrolysis with magnesium, until 

 the wire had crumbled away to a white powder. The liquid was 

 filtered off from the precipitate ; the latter was washed on the 

 filter, and then dissolved in dilute sulphuric acid. After evapo- 

 rating this liquid, 0*328 grm. of sulphate of magnesia remained, 

 which is equivalent to 0*0656 grm. of magnesium, or 61*1 cubic 

 centims. of hydrogen. 62*5 cubic centims. of hydrogen had 

 been given off. It is thus seen that no appreciable quantity of 

 magnesia had been dissolved. 



Solution of chloride of sodium was now decomposed between 

 magnesium electrodes, and, after the black precipitate had been 

 converted into the white powder, the above process repeated. 



* See my own researches, in Poggendorff's Annalen, vol. lxxvii. p. 504. 



