260 



Dr. A. E. Everest. 



Noting that the colour reactions of the anthocyans described by Willstatter 

 as resulting from the addition of alum in aqueous solution were always the 

 same as those produced by ferric chloride in aqueous solution, it occurred to 

 the author that the reactions obtained by Willstatter with alum may possibly 

 have been in reality the iron reaction, due to the use of impure alum contain- 

 ing traces of iron, whilst the author's failure to obtain the reaction with his 

 pigment was due to the fact that, on account of the knowledge that a ferric 

 chloride reaction was given by the pigment, an alum free from iron had been 

 obtained for the test. To test this, a sample of commercial alum was obtained 

 and used, whereupon the reaction was obtained exactly as anticipated, and as 

 described by Willstatter. The presence of an exceedingly small trace of iron 

 in the sample of alum originally used by the author was shown by adding a 

 very considerable bulk of it to a small quantity of the solution of the pigment, 

 when the colour reaction slowly appeared (No. 3, below). 



Reagent. 



1. Dilute solution of pure alum 



2. Saturated solution of pure alum 



3. Saturated solution of pure alum with 



addition of considerable quantity of 

 excess solid 



4. Dilute solution (same concentration as 



No. 1) of commercial alum 



5. Dilute ferric chloride (aqueous) ca. 6 per 



cent, solution, ^ drop 



6. Very dilute aqueous ferric chloride, O'l c.c, 



containing 0'000015 grm. ferric chloride 

 6a. Dilute aqueous solution of ferric sul- 

 phate, 2 drops 



7. Dilute ferric chloride, as No. 5 



8. Dilute aqueous solution of pure alum 



9. Dilute aqueous solution of commercial 



alum 



10. Dilute aqueous solution of ferric sulphate 



(same soiution as No. 6a), 2 drops 



11. Solid, finely divided ferric sulphate 



12. Test No. 11 on dilution with water 



When added to solution of the crystalline 

 chloride in faintly acid aqueous solution, 

 produced 



No colour change. 



Slight and very slow change towards purple. 

 Slowly purple, then pure blue. 



Very soon purple, then pure blue. 

 Immediately through purple to pure blue. 

 Very soon purple, then pure blue. 

 Very soon purple, then pure blue. 



When added to solution of the pigment 

 in faintly acid ethyl alcohol — 



Immediately through purple to pure intense 



blue. 

 No colour change. 

 No colour change. 



No colour change. 



No colour change, even on standing, only 

 slight change of tint towards purple. 



Rapidly passes through purple to fine pure 

 blue. 



The fact that the addition of alum, containing iron, to an alcoholic solution 

 of the colouring matter fails to give the reaction is thus shown to be due to 

 the iron being in the form of the sulphate. 



