233 50r.LV/ClL GAZETTE [march 



reaction (P„) their solutions establish when mixed with bark and 

 pyrogallol (table VII). The reaction established by the chlorides, 

 however, can hardly be responsible for the decrease in oxidation 

 they bring about, since sulphates, giving about the same reaction, 

 cause a small increase in oxidation. For example, a mixture of 

 potassium chloride, bark, and pyrogallol has a P H of 5 . 19 and gives 

 only 63 per cent as much oxidation as the control. A similar 

 mixture containing potassium sulphate has a P H of 5 . 13 and gives 

 7 per cent more oxidation than the control. The corresponding 

 figures for manganese are: manganese chloride mixture, P H = 45o, 

 oxidation = 104 per cent of the control. 



The situation for nitrates shows several irregularities. Potas- 

 sium nitrate giving a P H of 5 . 14 has practically no effect on oxida- 

 tion. Magnesium nitrate is also without effect, but gives a P H of 

 4.62. The nitrates of calcium, barium, and manganese inhibit 

 oxidation, but manganese gives a lower P H and the other two a higher 

 one than that given by magnesium nitrate. 



The results presented justify the conclusion that when o . 1 N 

 solutions of the salts are used, other ions than hydrogen and 

 hydroxy! play an important part in controlling oxidation. When 

 hydrogen or hydroxy! ions are neutralized in making oxidase 

 activity determinations, therefore, it is important to take into 

 consideration the possible effect of the salts formed thereby. This 

 must be considered as merely preliminary to the real investigations 

 of the relation of specific ions to the oxidation processes in plants 

 and animals. The effect of iron and manganese salts has long been 

 known, but more work is necessary, both with these and with 

 the more commonly occurring chlorides, sulphates, and nitrates of 

 other cations. 



Summary 



1. One-tenth normal solutions of all of the chlorides tested 

 (potassium, sodium, lithium, caesium, ammonium, calcium, man- 

 ganese, ferric) decreased oxidation of pyrogallol by apple bark 

 powder. 



2. Oxidation was increased very slightly by 0.10X solutions 

 of all the sulphates tested. 



