318 REPORT — 1886. 



Further considerations, which cannot here be given, show that if the con- 

 ductivity of a mixture of acids is calculated on the assumption that solutions of 

 equal conductivity are isohydric, the probable error amounts to 1 p.c. : being 

 rather greater if the strengths of the acids are very different, and less if they are 

 nearly equal. 



0. Supplementary remarhs. — The different bases have also been examined in a 

 perfectly similar manner. The results obtained are strictly analogous, including 

 the equality of the conductivities of isohydric solutions. But the carbonic acid 

 of the air had produced a disturbing effect to such an extent that the numbers 

 are too uncertain for publication. I have also found that acetic acid (^1*166) is 

 isohydric with ammonium acetate (0'469). The ratio of the conductivities of the 

 two (2'48o : 1 ) is nearly the same as the ratio of the maximum values of the con- 

 ductivities of acids and salts (2-83 : 1 according to Kohlrausch). This seems to 

 point to the conclusion that an electrolytic or active molecule of an acid, in 

 water, at ordinary temperature conducts 2-83 times as well as an electrolytic 

 molecule of a salt ; and not that in extreme dilution the acids are any more loosely 

 combined (' disagregirt ') than the salts. This arises probably from a smaller fric- 

 tion of the ion H of the acid (probably also of the OH of the bases) with respect 

 to the water, in which it also occurs as an ion, than occurs with the other ions. 

 This difference might disappear at higher temperatures. 



From the hypothesis that the different electrolytes divide the water between 

 them, there arise relations which promise to explain some very curious phenomena. 

 If for example a weak acid or base and a neutral salt are dissolved in water, 

 isohydric solutions will be formed in which tlie weak acid or base will get extremely 

 little water. In consequence, its molecular conductivity, and accordingly the 

 number of active molecules, will be very considerably diminished. I anticipated 

 this on other grounds in my paper of 1884,' and endeavoured in that way to 

 explain that the weak acids prove to be much weaker on mixing with bases than 

 they are for the same concentration when no other bodies ai-e in the same solution. 

 Tlie same hypothesis may also explain the great depreciation of strength of weak 

 acids when neutral salts are present, as calculated from the rapidity of reactions,- 

 and of the weaker bases in saponification reactions. I am still engaged upon the 

 solution of similar questions. 



•On the Verification of Faraday's Laiv of Electrolysis with reference to Silver 

 and Copper. By W. N. Shaw, M.A. 



Since the time of Faraday his law of electrolysis has not been subjected to any 

 Tery extensive experimental investigations. A. summary of the results obtained is 

 o-iven in the article on Electrolysis in the ' Encyclopaedia Britannica.' The most 

 accurate verification appears to have been conducted by Soret, who attributes to the 

 law an accuracy of 0-2 per cent, for copper and silver. Buff" used different currents 

 and found the law verified by experiment to about 1 per cent., but the general im- 

 pression has been that the law was only true to a somewhat rough approximation. 



A practical acquaintance with the behaviour of an electrolytic cell of copper 

 sulphate shows that it is not necessnry to attribute the defect from the theoretical 

 value of the chemical equivalent obtained in that way to the failure of Faraday's 

 law. In depositing copper upon a copper plate it may often be observ-ed that small 

 but brilliant red crystals are formed on the deposit. These crystals under the 

 microscope are very beautiful ; they may probably be regarded as a suboxide of 

 copper formed by the action of the copper on the solution. A purple coloration 

 is, moreover, often formed on the cathode, and this is possibly due to the presence of 

 the same compound of copper. This secondary action produces, of course, a differ- 

 ence in the weight of the deposit formed, and the true amount of electricity which 

 has passed cannot be inferred either from the weight of the copper with the compound 

 ■or from the weight of copper remaining when the crystals have been removed. 



' ' La Conductibilite Galvanique des Electrolytes,' Partie II. p. 77 (see below, p. 3.57) 

 = Spohr, Journ.f. praU. Chem. [2], sxxii. p. 32. 



