Gums, Resins, 



104 



[August, 1910. 



are not likely to yield an appreciable 

 quantity of latex. Hence, unless the 

 latex alters its character as the tree 

 grows older, there is no reason for think- 

 ing it is less mature in a six or ten-year- 

 old tree than a fifteen or twenty-year-old 

 one ; both will have immature laticiferous 

 tubes as well as fully functional ones. 



The reason why the latex from young 

 stems and shoots yields an inferior rub- 

 ber may be associated with the fact that 

 this latex is contained chiefly in the 

 tubes formed in primary growth. These 

 may quite well differ in their conteuts 

 from (hose produced in the so-called 

 secondary growth, which is due to the 

 activity of cambium, and by which the 

 tree increases its girth. If there be any 

 truth in this supposition, then this will 

 account for the fact that the rubber 

 from Hevea trees under four years old, 

 and especially of Castilloas of a similar 

 age, is midway in strength between that 

 from the shoots and that from older 

 trees. In such young trees the primary 

 laticiferous tubes will still be yielding 

 some latex, which will mingle with that 

 from the secondary tubes, giving an 

 intermediate product. Later, the pri- 

 mary ones will become wholly com- 

 pressed by the growth in thickness, and 

 cease to give any latex, 



Further, direct testing of the rubber 

 seems now to be dispelling this notion 

 of an inferiority in the caoutchouc from 

 six to ten-year-old trees, as compared 

 with from older ones. Beadle and 

 Stevens have carried out interesting 

 vulcanisation tests with plantation rub- 

 ber and fine Para. They argue rightly 

 that, as almost all rubber is vulcanised 

 before use, the trials of comparison 

 should be made after, and not before, 

 vulcanisation. Their results are distinct- 

 ly favourable to plantation rubber. Tests 

 for tensile strength and elongation at 

 the moment of rupture gave results 

 equal, if not superior, to those of fine 

 Para. They consider therefore that the 

 statement that plantation rubber is 

 wanting "nerve" is not justified, and 

 conclude that the new product will turn 

 out to be at least as good as, if not supe- 

 rior to, Brazilian fine Para. The vari- 

 ation in the quality of Plantation rubber 

 which is to be observed at times should 

 be attributed rather to differences in 

 the method of treating the latex than to 

 the age of the trees. 



Brief reference has already been made 

 to S pence's work on the protein in rub- 

 ber. By using suitable staining reagents 

 he was enabled to demonstrate a fibrous 

 reticular structure in raw Para rubber-, 

 due to the distribution of "cured " pro- 

 tein throughout the mass. He considers 



that it most likely plays an important 

 part in the quality of the rubber, add- 

 ing notably to its strength, and thus is a 

 desirable adjunct. To militate some- 

 what against this view is the fact that 

 in the processes of mastication and 

 vulcanisation such structure must most 

 likely disappear. However, as raw rub- 

 ber is sold on its strength, whatever 

 may add to this deserves consideration. 

 Protein in the uncured state is no doubt 

 a disadvantage at times, because such 

 rubber, if kept damp, will mould and 

 deteriorate. Even if protein be undesir- 

 able or inert, it does not seem to be 

 practicable at the present time to pre- 

 pare raw Para rubber without it. 

 Hevea latex will not submit to separ- 

 ation by centrifugal force, otherwise a 

 caoutchouc free from protein might be 

 prepared on a laboratory scale and then 

 compared with the article obtained by 

 coagulation. 



Further, the question arises : are all 

 caoutchoucs when pure, i.e., free from 

 resin, protein, etc., identical in physical 

 properties ? Is, for example, that of 

 Castilloa, Manihot, or Ficus equal in 

 every way to that of Hevea? They 

 possibly are, but there seems a probabil- 

 ity that they are not. In Hevea it has 

 been fairly well proved by Bamber that 

 the rubber from four-year-old-trees, 

 though inferior to that from older trees, 

 has the same chemical composition ; and 

 further the product from two-year-old 

 stems, though sticky and without 

 strength, showed little difference in 

 analysis, the slight increase in protein 

 and resin being too little to account for 

 the great difference in physical proper- 

 ties. Thus the gross chemical composi- 

 tion, as revealed by the ordinary me- 

 thods of analysis, is no criterion as to 

 the physical properties of caoutchouc. 

 There may be many varieties of this 

 substance, differing in elasticity and 

 strength, but identical as far as their 

 chemistry can be pushed. 



Synthetic Rubber. 

 The possibility of the production of a 

 commercial synthetic caoutchouc to com- 

 pete with the natural article has at 

 times perturbed the rubber-planter. A 

 few years ago the forthcoming of an 

 artificially prepared product looked more 

 hopeful than it does now. In the first 

 place a distinction must be drawn be- 

 tween a laboratory prepared and a 

 commercial synthetic rubber. The for- 

 mer has been an accomplished fact for a 

 number of years, and credit is due to 

 Professor Tilden for his work in this 

 direction ; no one since apparently has 

 advanced further than he did. A syn- 

 thesis of caoutchouc occurred in bia 



