4 



Prof. A. J. Ewart. 



hot alcohol, separating with petrol ether, and allowing the strong chloro- 

 phyll solution to stand in contact with a little water for some days in 

 the absence of light and oxygen. Small red particles of carotin separate 

 out, which can be collected and washed with cold absolute alcohol. 



To obtain larger quantities, the cortex of carrots can be grated, rubbed up 

 with water, and then all the juice pressed out. On boiling the red liquid 

 a scum of red carotin separates. This, after washing, can be dissolved in a 

 minimum quantity of hot absolute alcohol, filtered hot, and allowed to 

 stand. Most of the carotin separates out, and all of it if a little water 

 is added. The residue is washed with water, then with a little cold 

 absolute alcohol, dried, dissolved in petrol ether, and filtered. 



All the processes must be carried out as far as possible out of contact with 

 the air, and in darkness or very feeble light. When prepared, the solutions 

 of all three pigments must be kept in small tightly stoppered and completely 

 filled bottles in darkness until they are needed. Under these circumstances 

 all three pigments keep for a long time without appreciable change. 



The " lodoxidase " Action of Chlorophyll in Light. 



Wager concluded that one of the products of the decomposition of 

 chlorophyll in light was " an active chemical agent capable of bringing about 

 the liberation of iodine from potassium iodide," and that it was possibly an 

 organic peroxide and was a gas (p. 394). The action is easily obtained by 

 tinging potassium iodide and starch paper with a little chlorophyll, moisten- 

 ing and exposing to light in moist air. I am not, however, able to confirm 

 Wager's statement that blue light will liberate iodine from potassium iodide. 

 It must be remembered that the reaction is a very delicate one, which may 

 be produced by a variety of causes. Touching the paper with the fingers or 

 contact with the cork of a flask may cause a blue colour to be given on 

 exposure to light, the presence of traces of acid, of certain organic or 

 metallic oxidases will have the same effect, as well as traces of various gases 

 often present in the air. Certain kinds of paper on moistening with 

 potassium iodide and starch readily turn blue in sunlight, and may even 

 develop a weak peroxidase reaction with guaiacum. Pure, well washed 

 Swedish filter paper is free from this defect and may be used with safety. 

 An important point is, also, that the solutions used must be perfectly neutral. 

 Freshly prepared alcoholic chlorophyll is faintly acid, but the purified petrol- 

 ether solution is neutral. Films of the former liberated iodine very readily 

 in sunlight. 



Wager found that paper tinged with eosin or methyl green would also give 

 an " iodoxidase " reaction on exposure to light. Not only is this the case, 



