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Saps and Exudations. 



The Use op Drip Tins.— The announcement of the use of drip tins in 

 the book on rubber referred to was the first intimation of this invention. These 

 are patented by Mr. Geo. S. Brown, of Messrs. Brown and Davidson, Talawakele, 

 and a good idea of their use may be obtained by seeing the rough tins in use 

 at Henaratgoda. Chemical is not yet used in these, nor is the drip properly 

 regulated, but the absence of scrap by the use of water even is very notice- 

 able. Ammonia or formalin prevents the clotting of the latex which continues 

 to flow assisted by the dripping of these chemicals from the drip tin ; and 

 sufficient chemical is in the tin to keep the latex going until the wound is 

 practically sucked dry. No scrap whatever is found in the cuts, and when one 

 considers how much time each cooly has to spend in pulling the scrap out of 

 ordinary cuts, it is seen what a great labour-saving device these drip tins are, 

 as well as enabling all the rubber to be made into sheet or biscuit and having 

 no poor grade scrap. Once more we were among the bigger grove of trees, 

 and a very interesting sight was a coolie with a supply of white clay build- 

 ing up little canals on the trunks of trees tapped on the half herring-bone 

 and half-spiral systems. Again, the Scientist was appealed to. 



" It's well-known that the milk tubes run vertically in the bark, so that 

 to obtain a flow an oblique cut is advisable and a vertical one is useless ; 

 therefore the vertical channel cut in the half herring-bone or the half -spiral is an 

 extra strain on the recuperative powers of the tree, and does not produce any 

 latex— in fact it is useless. Moreover, the vertical cut relieves the tension in the 

 tubes and thus hinders the flow. We can get over this in two or three ways. 

 First, in this set of trees we have the half -herring bone or half-spiral cuts without 

 any vertical channel, and the milk from each cut runs out on the little patent 

 tin spout fixed at the bottom of each. Each spout is a little longer than the 

 one above, so that the milk drips from one down to the next below, and so 

 on to the collecting pan at the base. But in this other set of trees we have 

 a little clay channel or canal built up the tree and each side cut running into 

 it. This does away with the use of the spouts, and there is no need for the 

 vertical cut." 



A cooly's task is 25 trees clayed per day, and once done the clay canals 

 should last a long time. But time was rapidly fleeting, so we returned to the 

 small rubber house which for the nonce was turned into a chemical lab. 



THE LATEX AND ITS COAGULATION. 



If any planter who reads these notes has done his duty and read the latest 

 book on rubber he will have learnt something of the nature of rubber latex. He 

 will know that latex is chemically neutral or slightly alkaline ; and by practical 

 demonstration red litmus paper immersed in it remains red, and blue litmus remains 

 blue. In latex there are certain proteids (nearly 3 per cent, in prepared rubber) 

 and also various sugary substances (mosite, matezite, etc.). It is these that are 

 responsible for the growth of bacteria in dry rubber which produces decay and 

 " tackiness." These proteids in the latex remain in solution so long as the latex 

 is neutral or alkaline. If enough acid is added to more than neutralise the latex— 

 that is to make it feebly acid — the proteids, which are insoluble in acid, are 

 precipitated and the globules of caoutchouc are gathered together. This is coagula- 

 tion of the latex. So that for perfect coagulation you want to add just sufficient 

 acid to more than neutralise it. If too much acid is put in the latex the proteids 

 are redissolved, and after the milk is coagulated there still remains some proteid 

 and caoutchouc in the water— also the rubber is injured. The danger of using too 

 much acid is at once apparent, and the result is seen in many rubber factories where 

 the planter leaves the rubber water over for an extra 24 hours for the rest of the 

 rubber to coagulate. 



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