606 



The Supplement to the Tropical Agriculturist. 



Low Gbown. 

 '98. '99. '00. '01. '02. '03. ; 04. 'O.3.' 06. .'07 





c. c. . c. 



c. 



c. 



c. 



c. 



c. 



c. c. 



Weoya 



30 34 30 



34 



30 



35 



— 



— 



32 39 



Glencorse 



32 38 32 



33 



32 



37 



37 



30 



32 40 



Vogan 



34 38 32 



32 



34 



37 



36 



32 



32 39 



Kelani 



37 37 31 



31 



33 



36 



32 



27 



30 38 



Farnham 



38 37 32 



30 



31 



34 



— 



37 



30 40 



Knavesmire 32 38 30 



30 



29 



35 



— 



33 



33 39 



Polatagaraa 32 37 2S 



on 



31 



36 



34 



23 



o 1 Oft 



31 39 



Ganapalla 



30 36 31 



29 



30 



37 



31 



28 



2S 39 



Torwood 



32 38 31 



'29 



28 



34 



33 



29 



31 — 



Talagasw'la 



35 35 31 



29 



31 



38 



34 



34 



34 42 



Clunes 



33 36 29 



2S 



29 



35' 



29 



28 



29 39 



Hatdowa 



31 34 29 



26 



27 



33 



28 



'25 



23 33 





32 36 28 



25 



29 



31 



31 



26 



29 37 



—Local "Times," April 30th and May 1st. 



FORftllC AGED AS A COAGULANT FOR 

 THE LATEX OF HEVEA BRASILIEN- 

 SIS (PARA RUBBER.) 



By De. D. Spence. 



Although the number of substances which 

 have been tried experimentally as coagulants 

 for the latex secretion of rubber-producing 

 plants is legion, comparatively few of these 

 have ever been employed to any extent on an 

 industrial scale, and the number of reagents 

 now in actual use on rubber plantations in 

 connection with the coagulation of the latex 

 is limited to one or two well-known chemical 

 products which have found favour in virtue 

 of the fact that by their use large quanti- 

 ties of latex can be coagulated in a compara- 

 tively short space of time, without diminishing 

 appreciably the quality of the resulting product. 



It is unnecessary to enumerate here the 

 various chemicals which are still in use for 

 the coagulation of rubber latices in different 

 parts of the world. Acetic acid alone or in 

 combination with alcoholic creosote is now ex- 

 tensively employed on various rubber estates 

 in some parts of the world (in Ceylon and 

 in F. M. S. in particular). In connection 

 with the latex from Hevea brasiliensis acetic 

 acid has been found to exert an accelerating 

 influence in the process of coagulation of the 

 latex. Minute quantities of the acid are suffi- 

 cient in order to produce rapid coagulation, 

 and by the use of this acid in such quantities 

 the value of the resulting product does not 

 appear to be appreciably diminished. 



There is, however, another acid belonging to 

 the same series as acetic, and it is to this that 

 I should like to draw attention in the following 

 communication. This acid has grown into com- 

 mercial significance within recent years on 

 account of improved methods for its prepara- 

 tion, and it has been shown to have, in addition 

 to the general properties of the acids of its 

 series, another valuable property which acetic 

 acid and the others do not possess. This acid 

 is formic, the lowest member of the homologous 

 series, Cn H2n x 1 COOH, to which acetic acid 

 belongs. Formic acid shows all the general 

 reactions of the group, but, in addition, is 



known to have very marked antiseptic pro* 

 perties. Until recently this acid was com- 

 paratively expensive, and its use in industrial 

 processes was limited probably on this account, 

 but with the discovery of simpler methods of 

 preparation, the acid can now be turned out, 

 I believe, in large quantities at a moderate 

 cost, so that it is no longer to be looked upon 

 as a chemical of scientific interest only. 



Formic acid is a much stronger acid than 

 acetic, and belonging as it does to the same series 

 as acetic, I decided that it would be of interest 

 to try it as a coagulant for the latex of Heve'a 

 brasiliensis, and to compare its action with that 

 of acetic in this connection. 



The work of Victor Henri on the coagula- 

 tion of the latex of Hevea brasiliensis having 

 shown that coagulation of the latex emulsion 

 by acids is due to an increase in the H-ion 

 concentration in the system brought about by 

 the acid, one would expect, therefore, that 

 an aqueous solution of formic acid should be 

 many times more active in bringing about 

 coagulation of Hevea latex than a solution of 

 acetic acid of the same percentage strength. 

 This I have actually found it to be, so that 

 weight for weight formic acid is much more 

 economical than acetic for the coagulation of 

 the latex from Hevea brasiliensis. Nor is the 

 fact that formic acid in small quantities in raw 

 rubber has actually marked antiseptic proper- 

 ties of minor importance when considering 

 problems in regard to coagulation. This acid 

 would appear to be well worth the attention 

 of those who havo so far placed their faith in 

 the better known, but less active, acetic acid 



[We omit the technical details of the ex- 

 periments, and give Dr. Spence's conclusions: — ] 



The rubber obtained by coagulabing with 

 formic acid was in no way inferior in physical 

 properties or in chemical composition to the pro- 

 ducts obtained by using acetic acid ascoagulaut. 



To test whether the formic acid used in 

 coagulating the latex has antiseptic proper- 

 ties in the raw rubber, several samples of 

 the raw unwashed product obtained by coagu- 

 lating the latex in the above-mentioned way 

 wore exposed to conditions under which 

 decomposition or putrefaction would be liable 

 to take place in absence of a preservative 

 agent. The formic acid product was left ex- 

 posed for many months, alone and in im- 

 mediate contact with mouldy _ samples of 

 a West African rubber in which consider- 

 able decomposition had taken place. These 

 tests were carried out in the air at the 

 ordinary temperature and in the incubator 

 at 37" tX After exposure under these con- 

 ditions for several months the formic acid 

 rubber had become considerably drier, but 

 showed not the slightest signs of tackiness, 

 mould, putrefaction or the like. Formic acid 

 would appear, therefore, to have the property of 

 preserving moist unwashed samples of raw 

 rubber from decomposition. 



In conclusion, a quantity of latex was coagu- 

 lated by means of 1U per cent formic acid solu- 

 tion in 50 per cent alcohol and an equal quantity 

 of the same latex by the necessary amount of a 10 

 per cent acetic acid solution in 50 per cent 



