ON ELECTKOLTSIS IN ITS PHYSICAL AND CHEMICAL BEARINGS. 355 



' It sutEces to read the numbers in any horizontal row to see that they tend 

 towards the limit 1, not towards variable limits according to the nature of the 

 salt. The ratios deduced from the table of Kohlrausch agree very nearly with the 

 numbers in my first column for concentration —.' Polarisation is so strong at the 

 contact of metals with salts of Mg and Al that perhaps polarisation was not 

 altogether avoided by Kohlrausch for the case of the magnesium salts above. 



' To sum up : Molecular conductivities tend visibly to equality for hydrated as 

 well as for anhydrous salts, and the disagreement of my results with those of 

 Kohlrausch finds itself explained in the most satisfactory manner.' 



VI. Application of Faradai/s Law to the Study of the Conductivity of Salt- 

 solutions. 



' The law which I have just announced may be extended to a variety of salts. 

 It suffices to know the manner in which the salt is electrolysed, and what quantity 

 of salt is equivalent to KCl, for the application of Faraday's law.' 



The author then gives figures for various salts, classifying them thus: — 



«. Salts with several equivalents of acid. 



b. Double salts decomposed by water (including alums). 



c. Simple salts decomposed by vrater (tin salts and FeXH^^). 



d. Stable double normal salts (K^FeCy^, &c.) 



e. Double abnormal salts. 



f. Phosphates and arseniates. 



g. Bicarbonates. 

 h. Mercuric salts. 



i. Tartar emetic and a couple of cobalt compounds. 



He finds that HgClo, IIgBr„, and HgCy„ are unique ; they are insulators. Water 

 containing 5 grammes of one of these substances to the litre conducts very little 

 better than pure water : 200 times less than what the 4/m law would give. Sal 

 alembroth, however, conducts. 



VII. Organic Substances. 



Organic salts differ in no essential character from salts of which the acid and 

 base are mineral. If the electrolysis is normal the law of equivalents rigorously 

 applies, otherwise it does not, just as with mineral salts. 



Bodies like alcohol, glycerine, glucose, urea, &c. are very bad conductors, and 

 it is difficult to make sure that the feeble conductivity they show (when com- 

 mercially pure) is not due to the presence of traces of salts. 



VIII. Conductivity of very dilute Acids and Bases. 



The author has been led to the following conclusions : — 



^ Acids and bases which dissolve in xvatei- without combinim/ with if furnish 

 insulating solutions ; on the other hand, when these substances co7nbine with water in a 

 manner more or less complete they conduct in the same way as salts. 



' But a given acid or a given base often forms with water several different com- 

 binations. These combinations are usually unstable in presence of excess of water ; 

 they are dissociated more or less by elevation of temperature and bj' dilution. It 

 is only in a manner altogether exceptional that a monoba.«ic acid can exist in 

 dilute solutions in the monohydrated state, and without mixture with superior 

 hydrates ; its mode of electrolysis and its conductivity will vary in a corresponding 

 manner. It is therefore not legitimate to liken acids and bases in aqueous solution 

 to neutral salts ; the law of equivalents cannot be directly applied to them.' 



Then follows a twelve-page discussion of results, to establish these laws ; from 

 this I make a few extracts only. 



The case of sulphuric acid is interesting, since it can crystallise with either one, 

 two, or four, molecules of water, and it undergoes maximum contraction when 

 combined with six atoms. It is known also to possess a maximum conductivity 



A A 2 



