304 Prof. A. J. Ewart. Comparative Study of Oxidation by 



liquid which may remain colourless and may show a strong power of 

 ■decomposing H2O2 and turning guaiacum blue for a month or more at 

 12-14° C. The glycerine extract of the apple if half diluted with water 

 turns brown, and shows faint oxidase reactions after 10 days and none 

 after 15 days. The process of browning may weaken the oxidase in the 

 same way that it is weakened, and finally destroyed, by decomposing an excess 

 of hydrogen peroxide. 



The addition of a little of the glycerine extract to the sap from potato 

 cubes just killed by heat causes the production of a purplish -brown colour, 

 whereas the same amount of extract added to pure water produces no distinct 

 change of colour. 



When pulp is pounded with glycerine filtering is difficult and 

 prolonged. The best mode of obtaining the oxidase extract is by cutting 

 the pulp into minute cubes or thin slices, and placing these in glycerine for 

 five minutes, then pouring off the now diluted glycerine and replacing by 

 fresh glycerine. In this they may soak for 1-2 days. The glycerine can 

 then be strained off, and, if not diluted with water, keeps without dis- 

 colouring. 



If potato pulp is left in contact with glycerine it discolours on the 

 exposed surface in a few days, but, if well covered by glycerine, remains 

 uncoloured. Pounded pulp repeatedly extracted with an excess of glycerine 

 for three weeks and thoroughly washed with water remains colourless on 

 exposure to air, after the addition of fresh glycerine extract. Hence the 

 glycerine and water can extract the whole of the chromogen from the pulp. 



Nevertheless, the oxidase appears to cling with some tenacity to proteids 

 of the cell. Thus pounded potato pulp was allowed to brown, and then 

 washed till quite colourless, and the washing continued for an hour. On 

 testing the pulp it still decomposed hydrogen peroxide energetically and 

 gave oxidase reactions, while another portion remained colourless after the 

 addition of fresh glycerine extract. Evidently the chromogen is easily 

 removed by washing, but not the oxidase. Nevertheless, the latter is soluble 

 in water, for the clear filtrate from pulp pounded with water shows distinct, 

 though not very strong, oxidase reactions. 



The glycerine extract of apple pulp shows feebler oxidase properties than 

 that of the potato, and, when diluted, slowly turns reddish-brown on 

 exposure to air. 



A simple mode of rapidly obtaining an extract of potato oxidase free, or 

 nearly free, from the chromogen is to pound up to a paste, wash with 

 water, remove the pulp with a strainer, leaving the starch behind. 

 Squeeze out the excess of water, pound up with fresh water, settle and 



