Gums, Resins, 



10 



[July, 1910. 



with the protein or the so-called insolu- 

 ble constituent of the rubber." 



Why, it may be asked, does not Hevea 

 latex itself darken on exposure to the 

 air, and why, further, do some samples 

 of rubber prepared from it darken and 

 others remain light in colour ? 



Procedure on Estates. 



The " biscuit" was the earliest form of 

 plantation rubber to appear on the 

 market. The diluted latex, afte^ care- 

 ful straining to free it from all foreign 

 particles, and after the addition of the 

 necessary amount of acetic acid, is pour- 

 ed into fiat circular dishes. Coagulation 

 gradually sets in, and after twenty- 

 four hours the caoutchouc from each 

 vessel is capable of being removed 

 in the form of a spongy clot. This, on 

 being passed through a mangle, is com- 

 pressed into a thin circular piece of 

 opaque white rubber, which on drying 

 turns to a lightly coloured translucent 

 biscuit, 



Biscuits prepared in some such fashion 

 are still made on the smaller properties, 

 as no machinery is required, but on 

 large estates more economical ways of 

 procedure have been devised. 



Coagulation can be brought about 

 much more speedily by the use of a rotat- 

 ing machine, known as a coagulator, and 

 acting after the manner of a churn. 

 The latex with the requisite amount of 

 acid is poured into the coagulator, and 

 after a few minutes' rotation the clots 

 are formed. These are then passed 

 through a washing mill. Water plays 

 on the rubber, as it is masticated and 

 stretched in its passage through the 

 corrugated rollers, clearing out the 

 acid and impurities generally. The rub- 

 ber finally emerges in a continuous broad 

 ribbon, resembling crepe in texture, 

 which is readily dried. If smooth rollers 

 be use i then "sheet" rubber is made. 

 Sometimes the clots are cut up by a 

 special machine into small pieces, and 

 such rubber is known as " worms." 



Caoutchouc prepared in these different 

 forms is not fit for shipment till it is 

 dry, i.e., until the opaque whiteness 

 changes to a translucent pale amber 

 colour. Methods, therefore, of rapidly 

 drying the wet rubber have been intro- 

 duced. The quickest way is by means 

 of the vacuum dryer. The removal of 

 moisture by this apparatus entails a 

 fairly high temperature, which appears 

 to have a somewhat detrimental effect 

 on the quality of the rubber. The best 

 means of drying the newly-formed rub- 

 ber is still undecided, and the problem is 

 to some extent bound up with that of 

 curing. 



One estate is turning out a variety of 

 rubber known as "block," which is much 

 appreciated. It is made by compressing 

 in a special manner dry sheets or other 

 thin forms. There are distinct points 

 in favour of marketing plantation rub- 

 ber in this shape. It is convenient to 

 handle, and less surface is exposed to 

 oxidising influences. If the blocks be 

 made not more than an inch in thickness, 

 their homogenity can easily be verified. 



If blocks be made direct from the clots, 

 then the difficulty is to dry them in 

 short enough time to prevent moulding 

 and putrefaction. Here is shown the 

 value of a preservation. Willis and Bam- 

 ber a few years ago turned their atten- 

 tion to the feasibility of making " wet" 

 block by means of acid-coagulation in 

 the presence of creosote as an antiseptic. 

 They argued that a certain percentage 

 of moisture in raw rubber had a bene- 

 ficial effect on its keeping qualities. 

 Brazilian Para always holds about 10 per 

 cent, of water. Their wet block was 

 prepared directly from the clots by 

 pressure ; no trouble need be taken after- 

 wards to thoroughly dry it, since it is 

 permanently cured by the creosote. So 

 far this idea has not been put into 

 practise by the planters, neither have 

 buyers evinced a desire for this kind of 

 rubber. The chief difficulty would be 

 to keep the percentage of moisture con- 

 stant. Manufacturers naturally want to 

 know how much pure caoutchouc they 

 are buying in the raw article. At pre- 

 sent they know that dry plantation 

 rubber contains practically no extra 

 weight in the way of moisture. As some 

 one remarked, " Why pay freight on 

 moisture ? We can get enough of it in 

 Britain for all our needs ! " 



A word as to cleanliness; Planters 

 now see the great importance of 

 paying strict attention to this in the 

 preparation of raw rubber. Metal collect- 

 ing vessels, on account of their liability 

 to rust and so to stain the latex, have 

 been discarded in favour of glass. In 

 fact, as in butter and cheese making, 

 metal utensils and appliances should be 

 avoided as much as possible in the mani- 

 pulation of the latex. There is much 

 similarity between a rubber factory and 

 a modern dairy. 



(To be continued.) 



THE COMMERCIAL USES 

 OF RUBBER. 



(Prom the Indian Agriculturist, Vol. 

 XXXV., Mo, 4, April, 1910.) 

 Now that the rubber boom is at its 

 height, says The Economist, and the 

 attention of the speculating and invest- 



