ON COLLOID CHEMISTRY AND ITS INDUSTRIAL APPLICATIONS. 61 
ising, coagulating, washing, rolling, drying and sorting, grading, curing, packing, and 
a list of defects commonly met with and the preventives which can be adopted. 
* A Comparison of the Brazilian and Plantation Methods of Preparing Para Rubber,’ 
G. S. Watrey (‘ Journ. Soc. Chem. Ind.’ 1916, p. 493). Gives the results of com- 
parative tests on rubber prepared in the East by the Brazilian method, smoking and 
coagulation in thin films, and the typical plantation method of coagulation and rolling 
to sheets, followed by smoke-drying. Two series of samples were prepared, one from 
the latex from young trees (five years old) and old trees (fifteen years old). The con- 
clusions arrived at were that the rubber prepared by the Brazilian method was a little 
inferior to that produced by the plantation method. It was, however, suggested in the 
discussion following the paper that the Brazilian method of smoking had not been 
exactly imitated. There was little difference between the rubber from young and old 
trees. The following conclusions were also arrived at :—Phenols absorbed from the 
smoke reduce the rate of cure, and, generally speaking, rubber is not improved by 
smoking, and latex crépe may be very seriously deteriorated by this means ; ‘ oxida- 
tion’ has no ill effect on the quality, and, contrary to the generally accepted view, 
there is practically no difference in quality between the outer ‘ oxidised * portion and 
inner portion of a ball of fine hard Para. 
Comparative tests on rubber from groups of trees in different areas showed marked 
variation. Also latex allowed to stand before coagulation gave rather better results 
than that coagulated straight away. 
‘On the Coagulation of Hevea Latex and a New Method of Coagulation,’ B. J. Eaton 
and J. GrantwAm (‘ Agric. Bull. Federated Malay States,’ vol. 4, No. 2 (1915), p. 26). 
When latex is coagulated spontaneously by exposure to the air there is formed an 
alkaline scum on the surface where coagulation does not take place, while underneath 
the serum reacts acid and coagulation is more or less complete (G. S. WHITBY, 
‘Congress of Applied Chem.’ 1912; ‘ Koll. Zeit.,’12, 153). At the same time, strong 
putrefactive odours develop. The authors find that the putrefactive changes are 
inhibited while the development of the coagulating agencies have free play if a small 
quantity of sugar, e.g., 0°2 per cent. dextrine, be added to the latex. 
Eng. Pat. 104,323 of 1916, G, M. Taomas and M. D. Maupz, claims the process for 
allowing latex to coagulate spontaneously out of contact with the air, by which the 
formation of the surface scum is prevented. Eaton and GRANTHAM, however, state in 
the above communication that the coagulation is frequently incomplete when this is 
effected merely by exclusion of air, whereas in the presence of sugar coagulation is 
complete either under aérobic or anaérobic conditions. 8. Mor@an, however, finds that 
even in the presence of sugar coagulation is often incomplete (private communication). 
Other patents deal mostly with methods of evaporating latex in thin layers, as in 
» native Brazilian Para. 
* Bull. Agric. Intell.’ 1915-16, 1703-4. M. Kerroscu states that rubber obtained 
by evaporation of latex is less readily oxidised under the influence of sunlight than that 
produced by coagulation in the ordinary manner. 
(3) The Non-Caoutchoue Constituents of Raw Rubber. 
Nitrogenous constituent.—D. SrENcE was the first to show that the insoluble con- 
stituent of rubber (7.e., insoluble in organic solvents such as chloroform, benzene, &c.) 
was highly nitrogenous, and in fact consisted of protein matter coagulated with the 
eaoutchouc in the latex (‘ Journ. Liverpool Univ. Inst. of Commercial Research in the 
Tropics,’ No. 13,1907). Distribution of the protein in Para rubber. 
C. Brapte and H. P. Stevens subsequently showed that the nitrogenous or 
insoluble constituent was necessary for satisfactory vulcanisation, as its removal 
reduced the proportion of combined sulphur, and such rubber, vulcanised under normal 
conditions, had poor physical properties. It was also found that the nitrogenous con- 
stituent could be satisfactorily replaced by nitrogenous matter of foreign origin, such as 
peptone, and less satisfactorily by casein. The choice of nitrogenous substances was 
limited by the difficulty of incorporating them with the rubber. (‘ Koll. Zeit.’ 1912, 
11, p. 61, 1913, 12, p. 46; ‘ Journ. Soc. Chem. Ind.’ 1912, 31, p. 1099; H. P. Stevens, 
* Koll. Zeit.’ 1914, 14, p. 91.) 
D. Spence and G. D. Kratz (‘ Koll. Zeit.’) employ a *3—"5 per cent. solution of tri- 
chloracetic acid in benzene for separating the nitrogenous constituent. When the rubber 
is swollen in this solvent it rapidly breaks down, giving a solution of low viscosity from 
which the insoluble nitrogenous constituent is easily separated. Spence examined the 
