320 
As o , On the Nature of Oxidases. 
and after washing until the alkaline reaction disappeared, a por- 
tion of tliat para-aldehyde was distilled off. There was now 
observed tliat the iodine reaction above-mentioned did not take 
place neither at once nor within 15 minutes, bnt only an ex- 
ceedingly weak reaction slowly appeared later on, which howe- 
ver was not intinsitied by the addition of some acetic acid. 
The original para-aldehyde, however, gave an intense reaction 
within a few minutes. This difference was sufficient to prove 
that it is not the para-aldehyde itself, which causes the iodine 
reaction, but some impurity, which 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 hour. Tlierefore I can not agree with Bach and 
Cliodat 1 ) wlien they believed „daß die Gfuajakreaktion auf 
Peroxyde bei weitem empfindlicher ist als die Jodkalium-Stärke- 
Beaktion“. 
Also in regard to nitrites, both reagents were compared as 
follows: The tust was made with 0.01 %, 0,001 °/o, 0,0005 ° o 
and 0,0001 % solution of potassium nitrite with the following 
result: 
Concentration of 
N itrit e - s olution 
Potassium ioclid- 
starcli reaction. 1 ) 
Gruaiac, reaction 
0,01 °/ 0 
Distinct immediately 
Distinct immediately 
«/ 
0,001 °/o 
r> 
No reaction at once, 
but very faint blue 
after 15 minutes 
0,0005 0/ o 
V 
No reaction at once, 
only trace after 
Y 2 hour 
0,0001 % 
No reaction at once, 
very faint after 
15 minutes. 
No reaction at all 
From this table, it is cpiite clear that the guaiacum reaction 
is less delicate than the potassium iodid-reaction. Most of plant- 
juices produce very strong guaiac reaction, but no potassium 
iodid reaction. Hence the substance which produces tlie guaiac 
reaction must be cpiite different from that which produces po- 
!) Bei. D. Cliem. Ges. 37. p. 38. 
2 ) Of course, it is necessary to add. some acetic acid for tliis test. 
