August 1, 1912.] 



THE INDIA RUBBER WORLD 



527 



Coagulation — Its Technique and Chemistry. 



BEING the stage at which the article first assumes its perma- 

 nent condition, coagulation forms the most important and 

 critical feature in rubber production. Hence in discussing 

 the subject, it is advisable to consider it, under its various forms, 

 with reference, in the first place, to known processes. 



As Dr. Frank, of Berlin, the well-known rubber expert, has 

 pointed out, there are four basic methods : — • 



I. Smoking. 



II. Drying. 



III. Separation by Chemicals. 



IV. Mechanical Separation. 



I. SMOKING PROCESSES. 



Among the older processes of this class are those of Brown 

 & Davidson and Kerkhove. The process of Derry Dr. Frank 

 regards of a certain importance from a technical and experi- 

 mental point of view, as well as that of Cotinho (Dannin & 

 Mello, Belem), the products of which, exhibited last year in 

 London, met with his approval. Far more technically important 

 and more suitable for adoption, he considers the processes of 

 Cook (Shaw) and Da Costa (Bridge), which separate the rub- 

 ber from the latex without completely drying up the latter, as 

 occurs in the smoking process, properly so-called. 



The method usually adopted in South America is fuHy de- 

 scribed. Dr. Frank adds that the patented Shaw and Bridge 

 processes, as already mentioned, do not dry up the whole of the 

 latex with all its components, but effect a separation into a 

 serum and a coagulate. The latter (the rubber which has been 

 separated), when the process has been rightly carried out, is 

 uniformly penetrated by the component parts of the smoke. 

 These technical smoking processes, he remarks, may be consid- 

 ered more or less in conjunction with those in which chemicals 

 operate a separation of the rubber from the serum and its 

 components. 



Smoking processes, in the proper sense of the word, are 

 referred to as those of Derry, Cardozo, Dannin, and Wickham. 

 Those of Da Costa and Cook are specially mentioned as demon- 

 strating great technical progress. 



II. DRYING PROCESSES. 



Some kinds of rubber dry directly on the tree, without the 

 intervention of drying agents, and are taken out in the shape 

 of rubber. According to the degree of solidification attained, the 

 substance is simply removed in threads, and compressed into 

 large lumps, or wound. To this kind of process belongs the wild 

 preparation of Ficus rubber. Scrap of all descriptions of rubber 

 is generally obtained in wild and plantation culture through 

 drying, in many cases with the help of chemicals. There is 

 also, in some cases, simultaneous addition of certain decoctions 

 (such as tannic acid, soap, salt. etc.). Another important dry- 

 ing process in conjunction with the use of chemicals is the Leva 

 process, discovered by Dr. Hindorff and used in producing plan- 

 tation Mauiliot rubber. In this process, the tree is previously 

 coated with the extractive chemical solutions, the bark then 

 receiving a number of incisions with a rounded knife. The latex 

 which exudes coagulates while running down, and is gathered 

 from the trunk. 



A typical drying process, which has proved successful with 

 Kickxia latex in West African plantations, is that of Strauch, 

 in which the latex is let flow on boards, provided with ledges to 

 prevent overflowing. The wood absorbs a part of the moisture, 

 and the next day the latex has solidified into a smooth slab. 

 It is then removed from the wood and dried further. It has 

 been found necessary and advantageous in this process to pre- 

 viously add to the latex certain chemicals, such as purub, forma- 



line and other agents facilitating the separation of the rubber. 

 A direct tannin drying process for Funhitnia (Kickxia) was 

 first explicitly defined by A. Schulte. A certain quantity of 

 Funtumia latex is poured into a vessel resembling a pan, and 

 sprinkled with tannin solution. The vessel is then shaken, and 

 before long the mass can be turned in the mould like a pancake. 

 The still uncoagulated side is then sprinkled with tannin and 

 the movement continued. After a short time solidification has 

 so far progressed that the cake thus formed can be passed 

 through a wringer, which allows the watery serum which has 

 remained to partially escape. 



III. SEP.\RATION BY CHEMICALS. 



Many chemicals exercise a separating influence in the extrac- 

 tion of rubber from the latex. To a certain extent, the first 

 collectors of wild rubber used these influences as they existed in 

 the form of smoking and plant juices, as well as in soaps and 

 salts ; and in the natural forms of perspiration, saliva and urine. 

 It is not generally known that at one time rubber was extracted 

 by chewing from portions of plants. 



In the adoption of chemicals for plantation operations, as Dr. 

 Frank remarks, acetic acid was and has continued to be one 

 of the coagulants most generally used. He adds that according 

 to Schidrowitz, this process (originally suggested in Ceylon by 

 Parkin in 1898) is now used for coagulation in about 98 per cent. 

 of the plantation rubber produced. At the same time an English 

 expert has asserted that on account of its being coagulated with 

 acetic acid, plantation rubber is unsuitable for use in cables and 

 for other high-class purposes. 



Approval is expressed of the action of the carbonic acid 

 process, by which that agent separates the important inorganic 

 bases as indifferent salts, together with the rubber, throughout 

 which it is uniformly divided. It does not split up the albumin- 

 ous substances, but nevertheless apparently operates their separa- 

 tion. 



Dr. Frank cites a number of other chemicals and prepara- 

 tions, which can, in his opinion, be more or less recommended 

 for the extraction of rubber. These include formic acid, lactic 

 acid and homologous acids of this class, as well as citric acid 

 and tartaric acid. An objection seems to exist against oxalic 

 acid, on the ground of its taking up the indifferent salts of iron 

 and transforming them into soluble salts. Plant juices contain- 

 ing tannin, and plant decoctions (as well as phenole and creosote, 

 according to their degree of purity), are also referred to. To 

 the last named chemical group belong other alcohols of the 

 sebacic class. Finally, for a special purpose, formaline has proved 

 successful. Of inorganic substances, a number are indifferent, 

 this remark, however, not applying to common salt. Chloride of 

 calcium, on the other hand, seems to be more or less indifferent, 

 or even harmless. It is added that, on principle, metallic salts 

 should be avoided, particularly those of iron, copper, manganese 

 and quicksilver. Of the inorganic acids purub and carbonic 

 acid are spoken of as not only harmless, but even very favorable. 



Expert opinion seems to be more skeptical as to the general 

 use of sulphuric acid and muriatic acid. 



With respect to albumen. Dr. Frank arrives at the following 

 conclusions : 



1. All agents which precipitate and denatiirate albumen operate 



towards separating the rubber. 



2. Separating agents which exercise a decomposing influence 



upon the accompanying albuminous substance, or lead to its 

 decomposition, require in addition to the coagulating agent, 

 the simultaneous presence of preservatives. Substances 

 which do not exercise such a decomposing effect can be 

 used bv themselves. 



