r82 



of Para rubber. The process is simple and inexpensive, and if 

 the mechanical qualities of the rubber meet Dr. Weber's expecta- 

 tions when the practical tests of manufacturing have been applied, 

 it would seem that the essential requirements of the problem have 

 been met, and in any case valuable progress has been made. It 

 seems, moreover, from the investigations made by Parkin in 

 Ceylon that this method is capable of still further simplification. 



When the latex of Caatilloa is mixed with water and allowed to stand, in the 

 course of an hour or two the caoutchouc particles have all floated to the top in 

 the form of a thick cream. The diluted latex of Hevea, on the contrary, shows no 

 signs of creaming, even when submitted to a low temperature. .The difference is 

 most likely due to the larger size of the caoutchouc globule in the case of Castilloa 

 as compared with that of Hevea.* 



Parkin found, however, an interesting difference between the 

 latex of Castilloa in Ceylon and that described from tropical 

 America by Biffen, in whose results Weber may be said to 

 acquiesce, since he holds that the albumens of Castilloa latex are 

 readily coagulated by alkaline solutions. 



The proteid of the latex of Castilloa elastica has also been investigated to some 

 extent by Biffen. He found that the latex gives an acid reaction, and that on the 

 addition of a little alkali it is coagulated. This he considered to be due to the 

 nature of the proteid which exists as acid albumen in the latex ; on neutralization 

 it comes out of solution and gathers together th-^ caoutchouc particles into clots. 



Now the latex of the Castilloa introduced into Ceylon (0. Markhamiana) does 

 not behave like this. On the very gradual addition of alkali to the latex or to 

 the filtrate (the liquid part of the latex without the globules of caoutchouc) no 

 coagulation or precipitation occurs. Alcohol causes a coagulation of the latex and 

 a copious precipitate in the filtrate, which is quite soluble again in water. Proteid 

 is present in considerable quantity, about 4 per cent, being indicated by analysis. 

 Coagulation is brought about neither by acids nor by boiling. Thus it looks as if 

 the proteid beloni^s to the class of albumoses. At any rate the type of Cistilloa 

 introduced into Ceylon differs in this respect itrikingly from that of the true 

 Castilloa elastica examined by Biffen. 



These facts are of interest, not only from their bearing upon 

 coagulation and function of latex, but because they indicate the 

 extent to which the latex and its constituents may vary under 

 different conditions of growth. Parkin is probably in error in the 

 idea that the latex with which he experimented belonged to 

 Castilloa Markhamiana. The tree which was introduced by Cross 

 from Panama to Ceylon is more likely to be the same as that 

 with which Weber experimented in Colombia. 



DISCOLOURATION OF CASTILLoA I.ATEX. 



Incidental to his principal discovery Dr, Weber reports several 

 observations of much interest, not alone in their practical signifi- 

 cance, but also as illustrations of the mistakes which can be made 

 in a subject so difficult of investigation as rubber. Thus it is 

 found that the milk of Castilloa contains not a trace of tannic acid, 

 the presence of which has often been inferred, presumably because 

 ferric chlorid produces the same colour reaction with latex as with 

 tannic acid, turning it dark green. This reaction Dr. Weber finds 

 to be due to the presence of a glucoside, which also gives the latex 

 its intensely bitter taste. The addition of tannic acid precipitates 



* Parkin, Annals of Botany, 14: 198, 1900. 



