150 Scientific Intelligence. 



SCIENTIFIC INTELLIGENCE 



I. Chemistry and Physics. 



1. On the Electrical Convection of certain Dissolved Sub- 

 stances. — In their investigations upon solution and pseudo-solu- 

 tion, Pictox and Lindee, have studied the nature of the electric 

 transmission which takes place by means of certain dissolved sub- 

 stances. In the case of arsenous sulphide, for example, the con- 

 ductivity of its solution is extremely low, the current passing 

 being in one case only Y'lO -6 ampere; and even this may be due 

 to traces of the oxide. The passage of this small amount of 

 current, however, is accompanied by the repulsion of the col- 

 loidal sulphide as a whole from the negative electrode. Using 

 other substances, it appeared that in colloidal solutions which are 

 too coarse-grained to pass through a porous pot and which show 

 a coarse-grained structure by the optical test,* such as arsenous 

 sulphide (y), ferric hydrate and silicic acid, it is impossible to 

 repel the dissolved substance vertically upwards as completely as 

 downwards ; a result due presumably to the action of gravity on 

 the large colloidal particles. If, however, high grade solutions 

 be employed, such as iodine, aniline blue and magdala red, which 

 are readily filterable and which do not contain particles large 

 enough to scatter light, then the substances can be repelled com- 

 pletely from the lower electrode, provided the solution is not too 

 strong. In the case of aniline blue, however, the repulsion is 

 complete even with 2 or 3 per cent solutions. If the solvent be 

 highly non-conducting, as carbon disulphide for example, then no, 

 repulsion is observed. Thus while iodine in an imperfectly con- 

 ducting medium was repelled from the negative electrode, an 

 electromotive pressure even of 210 volts failed to show repulsion 

 when the iodine was dissolved in carbon disulphide. The rapidity 

 of the repulsive action seems to vary with the current strength ; 

 while its direction depends on the chemical character of the dis- 

 solved substance. Thus ferric hydrate, which is basic, is repelled 

 from the positive electrode; while iodine and arsenous sulphide, 

 which are acidic, are repelled from the negative electrode. In the 

 case of the dyes mentioned, the result is not so simple; aniline 

 blue, for example, being repelled from the negative electrode 

 whether as disodium salt or as sulphonic acid. Hence hydrolysis 

 seems to take place, which in this case would give in solution 

 sodium hydroxide and sulphonic acid; so that the repulsion 

 is due to the latter product. A table is given showing the 

 results of an examination of a large number of substances in this 

 way. On mixing acidic and basic dyes, the aggregates form 

 lower grade solutions and are carried as a whole by the convec- 

 tion. By adding alcohol, however, dissociation appears to occur 

 and the dyes are repelled in opposite directions. The authors 



*See this Journal, III, xlix, 467, June, 1895. 



