350 REPORT— 1887. 



may be considerably changed by the addition of very small quantities of other 

 substances. 



By a long series of careful experiments Professor Ostwald has tried if there 

 existed a relation between the mono, bi, and tri valency of the acids, and their 

 molecular conductivities in very dilute solutions, which might be in inverse ratio 

 to the valency (100 : 50 : 33^) ; but it seems not to follow from his researches ; as, 

 in solutions of different acids containing only one molecular weight in grammes in 

 1,000 litres of water, the numbers for the molecular conductivities vary for the 

 monovalent acids between 112-5 (HBr) and 12-65 (isobutylic acid), for the bivalent 

 between 113-4 (H,,SO^) and 16-91 (succinic acid). The different changes of the 

 molecular conductivities with increasing dilution (from 100 to 1,000 litres of water 

 for H.,SO^ fi-om 102-7 to 113-4, for isobutyric acid from 4-41 to 12-65, &c.) cannot 

 encourage us to a very far extended extrapolation which might conduct to the 

 above law. 



Therefore at present we must content ourselves with some minor regularities. 



One of these has been observed in the laboratory of Professor Eilhard 

 Wiedemann by Dr. Hartwig. According to his expeiimeuts the conductivities of 

 the acids of the fatty series attain with rising concentration their maximum the 

 earlier the more carbon they contain, and the later the more carbon the dissolving 

 medium (water, methylic, ethylic, amylic alcohol), contains. 



V. Also the attempt to measure the chemical strength of the acids by their 

 molecular resistances seems to me to depend upon an erroneous conception. Already 

 in my 'Galvanism 'I have mentioned that the electrical resistance oflers no measure 

 for the so-called ' force of decomposition,' and therefore, also, not for the chemical 

 affinity. May we assume the former view, that the ions of a compound are directly 

 separated by the current, or, according to the now generally received theory of M. 

 Clausius, that their motion is directed, or accelerated by it in a certain direction ? 

 After its interruption the electrolysed solution between the electrodes and far from 

 them is quite unchanged. The work done by the current in separating the ions or 

 changing their motion is totally regained by their recombination or their return to 

 their former state. 



The chemical affinity, or, more rightly, the heat of chemical combination, is 

 measured by the electromotive force ; and I believe that the law of Sir William 

 Thomson, that me electromotive force of a cell is equivalent to the heat evolved in 

 it, is true, if only we distinguish between the true primary chemical processes, 

 which alone determine the slectromotive force, and the secondary ones. For 

 instance, in the magnesium cells we must calculate amongst the primary processes 

 the formation of a highly negative suboxide of magnesium, in the cells with two 

 liquids we must consider that their ions at their plane of separation appear and 

 combine with each other in single atoms, while we measure directly their heat of 

 combination when bound together into molecules, &c. In my ' Treatise on Elec- 

 tricity,' vol. ii. p. 892, I have, though but in a very few words, indicated some of 

 these circumstances, which may explain the apparent objections to the law of Sir 

 William Thomson. But these considerations would lead us too far from our proper 

 subject. 



VI. More intimate appear the relations between electrical resistance and the 

 time for the formation of chemical compounds. In fact, this time depends (Ist) on 

 the affinity of the elements entering into combination or being exclianged between 

 two compounds ; and (2nd) on the mechanical resistance which they find, while 

 approaching each other, and which mostly has been totally neglected in these 

 questions. Both conditions must find their expression as well in the modern 

 theory of atomistic and molecular motion as in the older one. The first of these 

 conditions does not enter into the consideration of electrical resistance, the second 

 does ; so that even when in both cases the processes were quite the same, we could 

 not expect a proportionality between the time of combination and electrical 

 resistance. Nevertheless, the experiments of Professor Ostwald,' though treating 

 very heterogeneous processes, indicate that between the time for the inversion 

 of cane sugar, the catalysis of acetate of methyl by different acids, and their 



' Ostwald, Juurn.fiir practi^che Chtmie, N. F. xxs, 1883, pp. 93-225. 



