92 



The Supplement to the Tropical Agriculturist 



VACUUM BRSED RUBBER. 



Talawakele, Dec. 11th. 



Dear Sir.— We venture to think that the 

 enclosed letter will interest you sufficiently 

 to give it your careful perusal. 



Mr. Livingston is a Consulting Engineer 

 in London oi very high standing and has had 

 perhaps more experience in Vacuum Drying 

 Plant than any qualified Engineer at Home. 

 Our own practical experience in curing Plantat- 

 ion Bubber goes to shew that the value of 

 rubber dried in these machines has not yet been 

 fully appreciated by the brokers. Rubber dried 

 in Passburg's Vacuum Chamber cannot be 

 injured in vacuum. — We are, dear Sir, yours 

 faithfully, 



BROWN & DAVIDSON, LTD. 



{True Copy.) 



19th November, 1908. 



Dear Sirs,— I am informed that Vacuum 

 Dried Plantation Rubber, if sent for sale as 

 taken from the Vacuum drying chamber, does 

 not secure such a good price, owing to the 

 sheets being sent adhering together. 



If the buyers understood that this adhesive- 

 ness did not arise from "tackiness" or from 

 overheating, but arose from the uniform con- 

 dition of Vacuum dried rubber, on the surface, 

 as well as between the surfaces, then I think 

 that this condition of adhesiveness would 

 appreciate rather than depreciate the price. 



By the old method of drying, the washed 

 sheets, crepe or towels were hung up and exposed 

 for weeks to currents of warm air. The oxygen 

 in the air coming in contact with the surface 

 of the warm moist rubber, sots up a certain 

 chemical action, called, I understand, oxidation, 

 which altered the nature and composition of the 

 surface of the rubber, making it feel hard to the 

 touch. Owing to this action on the surface, such 

 sheets lost their tendency to adhere together. 



Even if a heavy pressure be employed to 

 force them into blocks, such blocks when cut 

 through shew quite clearly the surface 

 lines of the sheets composing them, because 

 the rubber between differs in its composition 

 from that of the surface of the sheets. 



On the other hand, when the sheets are placed 

 in the Vacuum Chamber, the air is rapidly ex- 

 hausted, and before the rubber has got warmed 

 up, most of the air with its oxygen has been 

 removed, and chemical action upon the surfaces 

 of the rubber cannot take place at all, or oidy 

 to such a slight degree as not to be perceptible. 



The surfaces remain quite soft and elastic to 

 the touch, quite different from the hard rigid 

 feel of air dried sheets. — Owing to the surfaces 

 not having been oxydised such sheets adhere to 

 each other, and if they are pressed together in 

 the Blocking Press, immediately after having 

 been removed from the Vacuum drying cham- 

 ber they cohere 'or amalgamate together so 

 closely, that the block thusformed becomes one 

 homogeneous mass of rubber ; when cut through 

 it is scarcely perceptible that it has been com- 

 posed of a number of sheets. 



These blocks, lam told, bavoa ready sale and 

 secure best prices. 



I am informed that if the Vacuum dried sheets 

 are not blocked, but are exposed to the air after 

 being taken from the Vacuum Chamber for suffi- 

 cient time to practically oxydise the surfaces, 

 or if they are mechanically treated so that the 

 surface has a soft elastic feeling removed, and 

 the property of adhering together is lost, they 

 secure better prices. 



This has the appearance that having secured 

 a superior article, it is being converted into an 

 inferior one, owing to a misunderstanding as to 

 the reason of the sheets adhering together. 



Vacuum drying chambers are very largely used 

 by manufacturers in this and other countries, 

 and they are quite accustomed to the making of 

 Vacuum dried sheets adhering together, just as 

 they are taken from the Chambers. The block- 

 ing is quite to be understood as it is convenient 

 for transport and also for storing, as the mini- 

 mum surface is exposed to the action of the air. 



I have written you thus fully, because you 

 will come in contact with the buyers, and may 

 be able to clear away the prejudice which ap- 

 pears for no valid reason to exist against these 

 Vacuum dried sheets, and so prevent the ex- 

 pense incurred by the subsequent treatment to 

 which they are subjected.— Yours faithfully, 

 (Signed) ' JAES LIVINGSTON. 



RUBBER IN TONKBN. 



Accordingto the " Kew Bulletin,'' a new rub- 

 ber tree from Tonkin has now been recognised 

 aB a member of the genus Bleekrodea (Moracea). 

 The tree occurs practically all over the province 

 of Bao-Kan and in the adjoining southern parts 

 of the circles of Bao-lanc and Cao-bang. It is 

 rapid growing, much branched, and attains a 

 height of 40 to 50 teet. From a single tree, li 

 feet in diameter, as much as 1 lb. of latex was 

 obtained in the spriug, which yielded 676 per 

 cent, of caoutchouc. The rubber is indistin- 

 guishable from Para rubber. This rubber tree 

 was described in the " Bulletin Economique " 

 of July last.— H and C. Ma.il, Nov. 20. 



WEEDING EXPENSES ON MALAYAN 

 RUBBER ESTATES. 



(To the Editor, "India Rubber Journal.") 

 Deak Sir, — Many of your readers being much 

 interested in plantation rubber in the ques- 

 tion of the cost of bringing an acre of the same 

 to a production stage, I enclose for your infor- 

 mation a copy of a letter® from Mr A B Lake, 

 which 1 understand has appeared in the Straits 

 papers, on the subject of clean weeding. As a 

 planter of many years' experience in the 

 Straits, 1 can only endorse Mr. Lake's remarks 

 on the subject and add my note of warning. 

 In theory, of course, Mr. Cat ruthers is right. 

 I can point to various fields of rubber on the 

 estates in my charge which, owing to lack of 

 funds, at one time were allowed to get weedy 

 and the weeds periodically dug in. The trees 

 on these fields show better growth, age for age, 

 than those on adjoining fields, which were kept 



* Reproduced in T..V. and Magaziue of C.A.S. page 1?:', 

 Xov„ 1903. 



