1774 



RUBBER, GUM AND RESIN PLANTS 



RUBBER, 



GUM AND RESIN 



PLANTS. 



1281 - Hevea in Java. — I. Vriens J. G. C, Planting and Thinning of Hevea, in Mededee- 

 lingen van den Adviseur der A. V. R. 0. S. No. 4, pp. 45-49. — II. Stet., The Fall of 

 Young Leaves in Hevea. Id. pp. 59-60. Medan, 1916. 



I. Various opinions are held as to the advantages of close planting 

 of Hevea followed later by thinning out. The author puts forward the 

 special advantage of this method in the ujikeep of the ])lantations, and 

 expresses his personal opinion that it is best to plant the trees 24 X 24 

 feet apart as a maximum and 19 x 18 feet as a minimum. The young 

 plants should be very carefully selected from the nurseries. 



The plantations must be kept well thinned in order that light can 

 penetrate everywhere. Good drainage is essential and care must be taken 

 that the water has free outlet. Pruning should be avoided and the plan- 

 tations must be weeded every year. 



II. The leaves of Hevea sometimes fall in the young stage. This 

 defoliation alwaj'^s occurs after prolonged rains, and it is attributed to 

 climatic causes, as no trace can be found of the presence of any crypto- 

 gamic disease. 



1282 - Some Experiments on the Coagulation of Hevea Latex without the Use of Acetic 



Acid. — Gerter Dr. K. and Swart Dr. N. L- in M ededeelingen van de Vereeniging Rubber 

 Proefstation West- Java No. 6, Bandoeng, 19 16. 



Thea author gives as result of his investigations on the coagulation 

 of Hevea latex the following summary : 



1. If latex with an addition of 0.3 per cent of sugar is allowed to 

 stand overnight, coagulation occurs b}^ lactic acid fermentation, putre- 

 faction being inhibited. 



2. The so called slow coagulation of latex by means of small quanti- 

 ties of acetic acid (0.3 gr. per liter) is also caused by lactic acid from bac- 

 terial growth. 



3. In order to get complete coagulation by the sugar process the 

 addition of 20 to 25 per cent of water to the undiluted latex may be recom- 

 mended, this quantity being diminished according to the concentration 

 of the latex received in the factory. 



4. On a factory scale the following proportions have been used ; 



1.75 ly- lates, containing about 35 per cent of dry rubber. 

 50 ly- of water. 



400-450 gr. of sugar'. 



5 Under the above conditions the acidity of the serum after 18 

 hours has rather a constant value corresponding to 0.3 per cent of acetic 

 acid. 



6. The addition of serum of the former coagulation maj' sometimes 

 be of use inhibiting putrefactive changes. 



7. To prevent the formation of a coloured layer on the rubber it 

 is advisable to pour water on its surface as soon as coagulation is setting in. 



8. In laboratory experiments small quantities of bisulfite of soda 

 had no disturbing influence upon the fermentation : on a large scale however 

 the results hitherto have not been satisfactory. 



