(1) A shallow layer of latex is less likely to coagulate spontaneously (i.e., without the addition of a coagulant) than a deeper volume.
(2) The shallow layer, and also the surface of the deeper volume (where exposed to air), on standing will be found to develop a superficial film of finely coagulated particles, yellowish in colour, and having an offensive odour due to decomposition of protein matter.
(3) While this partial coagulation is confined only to the surface of a shallow layer of latex, it will be found that below the surface film of the deeper volume a much more definite coagulation has taken place. The coagulation will be practically complete, and the coagulum, apart from a spongy appearance, is normal in character. This coagulum is free from the offensive odour noted above.
(4) On testing the surface film of both the shallow layer and the deeper volume, it will be found to be alkaline in character; whilst the lower liquid surrounding the main portion of the coagulum in the deeper volume of latex is of an acid nature.
These observed facts are sufficient to indicate that there are apparently two distinct types of spontaneous coagulation, and that the latter takes place particularly where the latex is more or less out of contact with the atmosphere. We may, therefore, differentiate thus:
(a) In contact with air (aerobic): incomplete spontaneous coagulation, accompanied by yellowish slime, offensive in odour and alkaline in character.
(b) Out of contact with air (Anaerobic): Practically or wholly complete. There is no offensive odour under normal conditions and the serum is acid in character.
It is concluded[28] that there are present in latex, on collection in the field, two types of organisms. Those which work in contact with air (aerobic) show a tendency to prevent coagulation and to form an alkaline yellow slime on the surface of the latex. The others, which work in the absence of air (anaerobic), may, under favourable conditions, cause complete coagulation unaccompanied by any decomposition or offensive odour within a normal period. If air is rigidly excluded, the coagulum obtained is quite satisfactory for all purposes.
[28] “Preparation and Vulcanisation of Plantation Rubber” (Eaton, Grantham, and Day), Bulletin No. 27, F.M.S. Department of Agriculture, 1918; “De la Coagulation naturelle du Latex d’Hevea Brasiliensis” (Denier and Vernet), Comptes Rendus l’Académie des Sciences, No. 3, July, 1917.
This type of coagulation, without the employment of a chemical coagulant, and under anaerobic conditions, was the subject of a patent granted in 1914 to Messrs. Maude, Crosse and others. The process has been in use on Cicely Estate (Perak) for some years. With subsequent slight modifications the apparatus consisted in essential of a tank with a loose cover. The flanges of the cover were sufficiently long to dip into a water-seal surrounding the tank. Thus the cover may rise and fall without an inrush of air.