Vol. X. No. 244 



THE AGRiCULTUliAL XEWS. 



279 



RUBBER INDUSTRY. 



COAGULATION OF RUBBER LATEX WITH 



ACETIC ACID. 



An iiiterestino; article in the India- Ualiber Journal, for 

 May 27, 1911, by Mr. W. Crossley, F.I.C, draws attention to 

 the fact that much has yet to be learned concerning the pro- 

 cess of coagulation of r.ibber latex, in spite of the good work 

 that lias been done so far in connexion with the matter. 



The article goes on to- consider various circuni.slances 

 relating to such coagulation by means of acetic acid, 

 and shows that research into the literature of the sub- 

 ject indicates a large variation in the quantity of acid that 

 has been considered by different authorities to be iiece.'sary 

 for the purpose. Alter giving examples in illustiatinn, it 

 presents the results of recent experiments that have bi'cn 

 performed with latcK from Sumatra. This, unfortunately, 

 had been diluted to a considerable extent, but was normal in 

 other respects. The experiments .show that, ignoring the 

 coagulating effect of the acids present naturally in the latex, 

 1 part by weight of acetic acid coagulated 1,176 parts by 

 volume of latex. Allowing for the acid already pre.'^ent, it 

 was found, further, that the true coagulating power of 

 1 part by weight of the total acid was 575 parts by volume 

 of latex. These results are not of general application, 

 for as has been indicated, the latex used in the trial had been 

 diluted to an unknown extent. The point of interest is tliat 

 the action of the naturally occurring acid probably explains 

 the large discrepancy in the amounts of acetic acid that are 

 recommended by different authorities for coagulation. The 

 dilution of latex to different degrees, and the extent of time 

 during which this has been kept, between collection and 

 examination, form sufficient causes for the obtaining of resnit.s 

 that are not in agreement. 



The article mentions the well-known fact that, if the 

 amount of acetic acid is either too large or too small, 

 imperfect coagulation results, and attention is further ilrawn 

 to work, by Parkin, which led to the following conclusion: 

 'the percentage of acid neces.sary is proportional only to the 

 original volume of latex pre.sent, and is independent of its 

 dilution with water.' Experiments carried out l)y the writer 

 of the article support this statement, and the latter is shown 

 by him to hold good through a very long range of values. In 

 the work, the assumption is made that the coagulating 

 powers of the naturally occurring acids and of the acetic acid 

 are equal. Further investigations are required to determine if 

 this is true. 



In regard to the maximum quantity of acid that is 

 required for the purpose of producing .satisfactory coagulation, 

 details and figures are given of a test in which this was found 

 to be 10'4 times the minimum amount, and an experiment is 

 described further, which demonstrates that the factor obtained 

 by dividing the maximum amount of acid by the minimum 

 is not a constant, ' for with the same volume of latex, 

 and a fixed maximum amount of acid, the maximum 

 amount of acid allowable increa.ses with the dilution.' The 

 matter also explains why addition can be made of a large 

 excess of acid over the minimum required (as far as complete 

 coagulation is concerned), if the latex has been diluted; on the 

 contrary, it is less safe to add a large amount of acid when 

 the work is being done with normal, undiluted latex. 



Concerning to the adsorption of acetic acid when it is 

 used to coagulate Hevea latex, the writer does not find evi- 

 dence that this takes place to any great extent, and details of 

 trials are given which support this view of the matter. If 

 there is any chemical action while coagulation is taking place, 

 it must be constituted in the combination of the acid with 

 one or more substances in the latex, to form compounds 

 having an acid reaction. As far as adsorption is concerned, 

 the writer prefers to consider this as referring to such acid 

 as can only be removed from the precipitated colloid with 

 great difficulty, and an experiment is given to show that 

 a small amount of the acid is actually precipitated in this way. 



The article concludes by a consideration of the effect of 

 the quantity of acid employed for coagulation on the protein 

 content of the finished rubber. It was found that the 

 l.irger the amount of acid, the greater the quantity of protein 

 found in the rubber, and this shows that, under present con- 

 ditions, it is preferable to use the minimum quantity of acid 

 that will produce coin|ilete coagulation. The subject is pur- 

 sued by the pcrloiinance of an experiment in which Hevea 

 latex- was lepeatedly shaken up with fre.sh quantities of water, 

 when it w..s found that the proteid content could be reduced 

 to a certain degree, and that rubber was obtained which 

 posse.'^sed an e.\-ceptionally light colour. No further evidence 

 is required to demonstrate the fact, at least, that the colour 

 of rubber is largely influenced by the way in which it is 

 prepared. 



THE SUPPLY OF RUBBER TO THE 



UNITED KINGDOM. 



The following table shows the imports of rubber to the 

 I'nited Kingdom in 1909 and 1910:— 



1909. 1910. 



Origin. Cwt. £ Cvvt. £ 



Gambia ... ... 221 3,379 103 2,268 



Sierre Leone ... 866 13,607 1,076 26^385 



Gold Coast 23,276 272,370 28,730 482^328 



.Southern Nigeria... 8,112 94,044 20,351 316^655 



Northern Nigeria — — 50 905 



Natal 1,021 1,661 808 1,622 



Zanzibar 725 12,845 528 13,339 



East African Protec- 

 torate 1,733 47,005 2,989 94,600 



India 3,690 23,292 6,164 S4,286 



Straits Settlements 53,855 1,412,241 81,451 3,039,523 

 Federated Malay 



States 11,198 385,798 34,110 1,504,403 



Ceylon 11.117 348,183 20,796 880,575 



British Borneo ... 5 81 1,681 43,528 

 British West 



Indies 37 603 105 1,977 

 Other British 



Possessions 2,193 9,454 3,688 24,851 



Total, British 



Possessions 118,049 2,624,563 202,630 6,517,245 

 Total, Foreign 



Countries 582,013 11,513,641 674,339 19,579,544 



700,062 14,138,204 876,969 26,096,789 



(From the Supplement to The Chamber of Commerce 

 Journal, July 1911.) 



