677 



filly ill all directions tlie \\iiole range of tiie mixing-proportions, 

 by serial determinations witli decreasing quantities of more or less 

 diluted latex, and increasing quantities of acid, either diluted or not. 

 The ,, irregular series" being only found with the lower percentages 

 of rubbei', it was possible to determine completely the range where 

 these occur. In most cases, described in literature, the ,, irregular 

 series" have only be examined with one single or with a few con- 

 centrations, the higher or lower concentrations of the colloid not 

 being accessible. The latex, used for most of the observations to be 

 desciibed here, originated from a group of trees, fifteen years old, 

 in the experiment garden at the opposite side of the Tjiliwoeng at 

 Buitenzorg. The trees were tapped daily, with two cuts over "/« of 

 the circumference of the trunk, and the latex was used for exami- 

 nation between 10 a. m. and noon. The percentage of rubber (on 

 coagulation) varied from 31,0 to 32,8, and on the average amounted 

 to 31,8 7,; 'lie acidity was 0,02—0.04 N. (cf. ^ 8), the acids pre- 

 sent are principally carbonic acid, lactic acid and a little butyric 

 acid'). 



In 1922 complementary observations were made with latex from 

 a few groups of trees in the Botanical garden. 



§ 2. The phenomena of coagulation. 



With the proportions, as they are chosen in the practice of the 

 preparation of rubber, the coagulation of Hevea latex [)roceeds 

 slowly. After a quarter of an hour the liquid lias become thick, 

 with the consistency of porridge; gradually it begins to cohere, and 

 after one hour a coherent lump is formed, but still with milky 

 serum; only after a few hours the separation into a solid coagulum 

 and a clear serum, is complete. In other cases one causes the coa- 

 gulation to proceed more rapidly, by adding more acid, so that, 

 after one hour, one obtains a coagulum sustable for working 

 purposes. Or one saves acid, so that only after a few hours 

 the first phenomena occur, and the coagulum can only be worked 

 up next morning. Sometimes the latex is used undiluted, but mostly 

 one dilutes with water to a rubber percentage of 20 or 15°'„, on 

 account of which the coagulum becomes softer, and may be worked 

 up more easily. The more the latex is diluted, the softer the coa- 

 gulum becomes, and the stronger the contraction after the coagula- 



1) For the composition of Hevea latex in general we may refer to „Estate 

 Rubber, its preparation, properties and testing" by Dr. 0. de Vries (Ruygrok 

 & Co.. 1920), chapter 1 and 2. 



