Aso, Which Compound in certain plant-juices can liberate iodine etc. 213 



acid is present as potassiuni nitrite. A quantitative colorimetric 

 test with the bucls of Sagittaria showed that the amount of 

 potassium nitrite was only 0.000 1 g . KNO> per shoot (fresh) 

 = 0.0135 °/o in average. Five buds weighing in the fresh state, 

 3.7 g. were crushed and extracted with 50 c. c. of boiling hot 

 water; after ten minutes, the extract was filtered off 10. c. c. of 

 the filtrate were now mixed with 1 c. c. saturated Solution of 

 sulphanilic acid, then with two drops of dilute sulphuric acid, 

 and after two minutes, 2 c. c. of a dilute Solution of c.-naphty- 

 lamine hydrochlorid were added. At exactly the same time a 

 highly diluted Solution of potassium nitrite in different degrees 

 of concentration were treated exactly alike. The characteristic 

 red reaction of considerable intensity set in at once with the 

 extract and the colorimetric comparison with the other tests 

 showed that the reaction corresponded nearest to that of KNO% 

 in a dilution of 1 : 100000. 



Since the question is of some interest whether this nitrite 

 is formed by reduction of nitrate or by oxidation of ammonium 

 salts, I have tested the bulbs with diphenylamine, but no 

 reaction was obtained, hence neither nitrates nor nitrites were 

 present in the bulb. The boiled juice of the buds was also 

 poured carefully on the surface of diphenylamine Solution in 

 concentrated sulphuric acid, and here soon a blue ring was 

 observed, doubtless due to the small quantity of nitrite present. 

 We can therefore infer that the nitrons acid in the buds is 

 formed in analogy to the nitrification process by oxida- 

 tion of ammonia. 



I have further compared the reaction of potassium nitrite 

 in the dilution of 0.001 % upon potassium iodid-starch paste; 

 and obtained a blue color of nearly the same intensity as with 

 the above mentioned extract of the buds. 



It would be naturally of importance to prove in a great 

 number of cases in which the iodine reaction is obtained that 

 also the G-riess reaction for nitrites can be observed. But here 

 I encountered an unexpected obstacle. There occur certain 

 Compounds related to the thannins, that can prevent the reaction 

 of Grriess. Some trials have convinced nie that not only 

 phloroglucin and hydrochinon and common tannin, but also the 

 juice of bean shoots and an infusion of green tea can prevent 

 the reaction of Grriess 1 ). Such peculiar preventive Compounds 

 happily do not occur in the buds of the Sagittaria bulb. This 

 yields only a slight greenish reaction with ferrous sulphate 

 while the shoots of bean give an intense black reaction. My 



*) Tests with asparagin, guanidine, methylamine and peptone have 

 however convinced me that these do not prevent the reaction of Griess, 

 if not too much time is lost. 



In regard to bean shoots it is of interest to note that shoot 12 — 15 cm 

 long will show the iodine reaction very piain, iy the uppermost 2 cm, but 

 not at the base and in the roots, while the guaiac reaction "was obtained 

 with every parts of the young plants. 



