A s o , Oll Hh> Natnre of Oxidascs. 



321 



tassium iodid starcli reaction tliat is, the fornier is caused by 

 oxidase very frequent in plantjuices, and the latter by nitrite 

 whicli is present in certain plantjuices, as I liad positively pro- 

 ved in one case (1. c. page 212). 



But if tlie iodine liberation by certain plantjuices would be 

 due always to traces of nitrite and not to enzyms, liow is tlie 

 fact to be explained that this property is lost in most cases^) 

 on heating? The probable answer is here that plantjuices are 

 often slightly acid and contain at the same time small quanti- 

 ties of amido-compounds. Under this condition traces of nitri- 

 tes must dissapear on warming, while after addition of some 

 alkali, the reaktion will probably be maintained after boiling. 



About 15 c. c. of 0,001 "'o potassium nitrite Solution were 

 mixed with an equal volume of 1 ojo asparagine sohition (aqueous) 

 and divided into three equal parts. To one part, I added a 

 drop of dilute acetic acid and to another, a drop of dilute caustic 

 potash free from nitrite while the third served as control. These 

 Solutions were heated to boiling for three minutes tlien about 

 1 c. c. of potassium iodid-starch Solution was added and to the 

 alkahne as well as the control Solutions also, some dilute acetic 

 acid to render the reaction slightly acid ; the result obtained was : 



This test was repeated: 30 c. c. of 0,001 % potassium nitrite 

 Solution were mixed with 30 c. c. of 1 % asparagine Solution and 

 divided into three parts. To one was added a drop of dilute 

 acetic acid, to the other a drop of dilute caustic potash Solution 

 while the third served as control. These Solutions were kept 

 boiling for live minutes and tested with potassium iodid-starch 



1) Once, 1 groiind foiir biids of Sag-ittaria with 20 c. c. water. The 

 pressed juice which produced strong reartion with guaiac tinctxire. Oriess 

 reageut as well as potassium iodid-starch was divided into two halves and 

 one was boiled for one miaute while tlie other served as control. Both 



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