596 EEPOET— 1881. 



ture, at a given tempei-atiire the extent of reduction increases, although at a 

 gradually diminishing rate, with the time of solution. The rapidity of solution 

 and extent of induction, produced by a given quantity of zinc of a given area and 

 in a solution of a given temperature and containing a definite weight of free acid, 

 increases v^ith the amount of reducible iron present. Experiments made by plac- 

 ing zinc in contact with platinum shovs-ed that, although the time of solution of 

 zinc in contact with platinum, is considerably diminished, as compared with that of 

 zinc alone, little difference in the reducing effect is observed. 



Similar results were obtained with magnesium, although the amount of reduc- 

 tion is from one-fourth to one-third of that produced by zinc, under similar condi- 

 tions. The diminution of the rate of solution with decrease in the amount of free 

 acid present, is far greater in the case of magnesium than in that of zinc. 



The author concludes that his experiments strongly support the view that the 

 reducing power of nascent hydrogen is connected with the existence of this body 

 in the atomic condition, since all conditions tending to prolong the duration of this 

 atomic condition augment the reducing power. 



6. On tlie Heducing Action of Zinc and Magnesium on Vanadium Solutions. 

 By Professor H. E. RoscOE, LL.D., F.B.8. 



The object of this communication is to examine the reducing action of the 

 above metals upon acid Vanadic Solutions, comparing the relative amount of reduc- 

 tion effected by metals generally, together with the time occupied by that reduction, 

 other conditions remaining as nearly constant as possible. From his original 

 experiments on this subject the author concluded that, whilst the reduction in the 

 case of zinc and sodium took place from V.^Oj to V._,0o, that in the case of magnesium 

 only proceeded to V^Oj. This he now finds is so far not the case that the same 

 point is in reality reached by all three above-named metals, but that the reduction 

 from V0O3 to VoOo takes place with magnesium with extreme slowness. Curves 

 of the reduction in terms of the time are gi-\en. 



7. O71 the Determination of the Relative Atomic Weiglits of Manganese, 

 Oxygen, and Silver. By Professor Dewar, M.A., F.B.S., and 

 A. Scott, B.A., B.Sc. 



Considerable doubt seems to exist as to whether the atomic weight of manganese 

 should be taken as 54 or 55. It seemed to the authors that by the use of perman- 

 ganate of silver this could be determined with great accuracy, as it is only needful 

 to assume the atomic weights of oxygen and silver, which are the two elements, the 

 atomic weights of which have been most accurately determined by Stas. It is an 

 exceedingly good substance for this purpose, as it can I'eadily be obtained in a state 

 of high purit}^. and can be readily weighed, as it is an anhydrous salt and is not hygro- 

 scopic in the slightest degree. It contains likewise manganese free from any allied 

 metals, and may be decomposed without the intervention of any solution. By 

 heating it to a temperature of about 100° to 105° it decomposes thus : — 

 4AgMnO, = 2(Ag20.2]\InO.,) + SO^ 



If this residue, which seems to be a comparatively stable and definite compound, 

 be heated in hydrogen we have this decomposition : — 



Agj02Mn02 + 3H2 = Ago + 2MnO + 3H,0. 



From these decompositions they expect very accurate results. As a further 

 check they dissolve the oxide of manganese out of this residue by means of dilute 

 sulphuric acid containing a little sulphurous acid, w^ash thoroughly and thus leave 

 the silver behind. The decompositions are done in a bulb of hard glass. Three 

 experunents, made on difierent samples of the salt, give the follomng values for 

 manganese, silver being taken as 108 and oxygen as 1 6. 



55-51 



64-04 



54-45 



