138 Dr. F. Auerbach on the Passage of 



sulphonic compound, having, as a rule, the formula 



C 20 H M (C. H 5 ) 2 . C 6 H 4 N 3 [NaSOJ. 

 Our own sample, which was prepared many years ago, may 

 possibly have contained a little of the disulphonic compound. 

 The solution which I employed contained *1 grm. in a litre, 

 being therefore three hundred times as strong as in I. and II. 

 When this was boiled, even for several hours, it refused to 

 bleach ; but on allowing the hot liquid to cool gradually, the 

 colour slowly faded away before the ordinary temperature was 

 reached. Kepeated attempts to decolorize the liquid by heat- 

 ing to temperatures short of 100° were all attended with 

 failure. 



When the decolorized liquid was kept for three or four 

 hours, or frozen, or mixed with a little hydric acetate, the 

 colour was restored. 



The dissociation-temperature for Nicholson's blue is obvi- 

 ously a little below the boiling-point of water. 



Phenomena of bleaching in connexion with Nicholson's 

 blue were first noticed by my friend Mr. Louis Campbell. 



XVIII. On the Passage of the Galvanic Current through Iron. 

 By Felix Auerbach, Ph.D., of Breslau. 

 [Continued from p. 18.] 

 § 7. "FN the following I will endeavour to elucidate the ob- 

 -*- served phenomena on the basis of the theory of rotable 

 molecular magnets. In so doing I make use of the conception of 

 work, defining it for the present case as the product obtained when 

 the force which must be overcome for the rotation of a molecular 

 magnet is multiplied by the angular quantity of that rotation. 

 The extra currents arising in iron have already been commonly 

 recognized as the expression of such performance of work. 

 When, from a fixed moment onwards, a current generated by 

 a constant electromotive force performs work which till then 

 it did not perform, then Ohm's law is valid only on the hypo- 

 thesis that either the current-intensity i or the resistance w 

 obtains another value. Assuming the former case, the equa- 

 tion is usually written 



a fe *, 

 %=■ — ■ > 



1 V 



that is, the quantity - -^- (in which a denotes the value of the 

 a o ^ 



* Helniholtz, Die Erhaltung der Kraft : Berlin, 1847. 



