320 



Aso, On tlio Niitufo of Oxirlases. 



and after washing until tlie alkaline reaction disappeared, a por- 

 tion of tliat ])ara-aldo]iyde was distilled off. There was now 

 obsorvc'd tliat tlie iodine reaction above-mentioned did not take 

 place iieitlier at once nor within 15 minutes, but only an ex- 

 ceedingly weak reaction slowly appeared later on, wliicli howe- 

 ver was not intensified by tlie addition of some acetic acid. 

 The original para-aldehyde , liowever, gave an intense reaction 

 witliin a few minutes. This difference was snfficient to prove 

 tliat it is not tlie para-aldeliyde itself, wdiicli causes the iodine 

 reaction, but some impurity, wliicli can only liave been the 

 peroxid above-mentioned, to judge from analogy. Now it was 

 interesting to observe that the original para-aldehyde which pro- 

 duced such an intense iodine reaction had no reaction what- 

 ever on tincture of guaiacum, not even on addition of 

 some hydrogen peroxid. These mixtures were still colorless even 

 after half an liour. Therefore I can not agree with Bach and 

 Chodat^) Avhen they believed „daß die Guajakreaktion auf 

 Peroxyde bei weitem empfindlicher ist als die Jodkalium-Stärke- 

 Reaktion''. 



Also in regard to nitrites, both reagents were compared as 



foUows: The fest was made with O.Ol 



0/. 



/o, 



0,001 ö/ü, 0,0005 % 



and 0,0001 % Solution of potassium niti-ite with the following 

 result: 



From this table, it is quite clear that the guaiacum reaction 

 is less dehcate tliaii the potassium iodid-reaction. Most of plant- 

 juices produce very streng guaiac reaction, but no potassium 

 iodid reaction. Hence the substance which produces the guaiac 

 reaction must be cpiite different from that which produces po- 



1) Ber. D. Chem. Ges. 37. p. 38. 



2} Of course, it is necessary to add some acetic acid for tliis test. 



