Gums, Resins, 



22 



a very weak rubber. The coal-tar which is in it seems to enter into some sort 

 of union with the rubber, making it sticky and destroying its strength and 

 elasticity. If an excess of strong sulpho-naphthol is used, a black pitchy substance 

 with the consistency of chewing-gum is formed. 



Acid will coagulate to a certain extent. Sulphuric acid when strong will 

 coagulate immediately ; when weak it does not coagulate at all. Rubber coagu- 

 lated by it is generally weak in proportion to the strength of the acid. Even 

 the strongest rubber formed by this means is eaten on the surface. Limejuice 

 will coagulate under certain conditions, but just what these conditions are I do 

 not know. I have not been able to coagulate by any other acids. No other 

 chemicals that I know of give certain coagulations. 



Sodium carbonate and calcium chloride have coagulated on certain occasions, 

 but this could not be repeated. There appears to be sometimes a sort of half -coagu- 

 lation. The latex rises to the surface, forming a thick sheet which cannot be blown 

 apart like ordinary latex, but which is not sufficiently solid to pick up. This half- 

 coagulation is affected by weak solutions of acid ; sulphuric, hydrochloric, nitric and 

 lime juice; by calcium chloride, sodium hydroxide, and sodium carbonate. No 

 matter how long such latex stands, it will not become rubber until something 

 farther is done to it. On the whole, dry coagulation is better than wet. I am of 

 opinion that the best coagulation will be found to be pressure between porous 

 tiles. This would make dry uniform rubber. It could be done mechanically, 

 and the tile could be made so as to print a plantation name or letter on the rubber. 

 —The Quarterly Journal, Liverpool. Institute of Tropical Research. 



{To be concluded.) 



Notes on the Cultivation and Manufacture of Rubber. 



OBSERVATIONS IN THE MALAY PENINSULA. 



Planting. — Even taking into consideration the increased expense, baskets 

 are distinctly preferable to stumps. 



Distances for Planting.— Opinion still varies greatly as to what is the best 

 distance to plant. Observations made on some of the principal estates on the Malay 

 Peninsula lead to the belief that anything less than 100 trees to the acre is an extra- 

 vagance, which present experience does not warrant. Anything more than 400 to 

 the acre has not been attempted so far as is known, though the gardens at Singapore 

 may be quoted as an exception. 



It remains to be proved whether or no close planting will ultimately give a 

 larger yield per acre than wide. That the yield will be largely in favour of close 

 planting during the first two or three years of tapping there can be no doubt, but 

 how long this advantage will last has yet to be ascertained. It has been advocated 

 that the trees should be planted close at first and subsequently thinned ; though it is 

 open to doubt if in the case of a field planted, say 10 x 10 ft., and thinned to 

 20 x 20 ft., the yield after the thinning will ever be as good as that from a field 

 planted at the wider distance. 



In view of the percentage of trees of comparatively poor growth that occurs 

 under all systems of planting, it seems advisable to plant at first such a number as 

 will provide a margin sufficient to maintain the number of trees to the acre at not 

 less than that desired when these failures have been cut out. In cases where wide 

 planting has been supplemented at a later date by intermediate rows of trees, these 

 appear to have universally failed. 



Everything considered it would seem 30 x 10ft., representing about 144 trees 

 to the acre, is the distance which offers the greatest advantages, giving as it does a 

 sufficient margin for cutting out a few weak trees, while the 30 feet between the 



