183 



the albumens of the latex, so that the presence of albumens is 

 itself deemed a sufficient evidence of the absence of tannic acid 

 in latex of any kind. 



The rapid colour change of the milk of Castilloa on exposure 

 to the air is found to be due to an enzym or oxydizing ferment 

 (oxydase) which is probably destroyed by the boiling water, as 

 suggested by Parkin to whose work Dr. Weber does not refer, 

 although in this part of the subject it had covered the same 

 ground. 



Parkin reported as follows : 



Several latices, which are pure white when they first issue from a wound on the 

 plant, rapidly darken on exposure to the air. This is due to the presence of an 

 oxydizing ferment, or oxydase, which with the aid of the oxygen of the air acts on 

 some constituent of the latex, changing it to a deep brown colouring matter. 



The latex of Castilloa is a good example. It rapidly darkens on exposure and 

 dries to an almost black rubber. By creaming the caoutchouc particles can be 

 separated fr im the dark beer-like liquid and made into a sheet of nearly colour- 

 less rubber. By quickly heating the collected latex the darkening is arrested 

 owing to the destruction of the enzyme. 



The latex of Hevea collected from the tre^ trunk does not darken at all on ex- 

 posure to the air, and provided that moulds and putrefactive organisms are kept, 

 away, rubber prepared from it remains indefinitely of a light colour. On the 

 other hand, the latex from the wall of the unripe capsule (fruit) changes on ex- 

 posure from milk-white to black. The darkening is wholly prevented if the latex 

 is quickly subjected to heat. No doubt there is an oxydase present in the latex 

 of the capsule, (a) 



The expression " coagulation of rubber" appears objectionable 

 to Dr. Weber because he finds that it is the albuminous substances 

 of the latex which coagulate and not the rubber itself, but this 

 objection seems rather over-technical, since, even in Dr. Weber's 

 method, the rubber is collected and compacted, and for this process 

 a name is still required. It is the albuminous substances in- 

 corporated in Castilloa rubber which continue to ferment and 

 putrefy, or otherwise contribute to the deterioration of the rubber, 

 both crude and manufactured. In other words, it is the albumens 

 rather than the resins which determine the inferiority of rubber, 

 and the amount of resin contained in the latex of adult Castilloa 

 trees is held to be "entirely innocuous" and " absolutely unobjec- 

 tionable." Dr. Weber continues : 



I am quite aware that now and then all sorts of sinister actions are ascribed to 

 the presence of resins in India rubber, but there is not the least particle of evi- 

 dence to show than they are intrinsically detrimental. As a matter of fact, in the 

 manufacture of quite a number of rubber goods, resins are deliberately added to 

 the mixings, (h) 



BOARD OF AGRICULTURE. 



Extracts from Minutes. 



The usual monthly meeting of the Board of Agriculture was 

 held at Headquarter House on the 13th June. Present : — the Hon. 

 the Colonial Secretary, Chairman, the Director of Public Gardens 

 and Plantations, the Agricultural Chemist, Mr. C. A. T. Fursdon, 



(a) Parkin, Annals of Botany, 14; 199-200. 1900. 

 (Z*) Tropical Agriculturist, 22: 444. .Innuary, IdO.S. 



