21 



Saps and Exudations. 



long, when it is likely to be in the rain also. I believe that rubber could be 

 easily sun-dried through glass without its becoming sticky. Another way is to 

 drain off the surplus water and to dry the latex globules remaining until they 

 coagulate. This is the blotting paper method. Blotting paper hastens the draining 

 by soaking up a good deal of water, but there is no reason why this method 

 could not be employed with any other paper through which water would drain, 

 such as chemical filter paper. The question of durability and cost of the papers 

 would come in here. Some objections have been made to the blotting paper 

 on the ground of expense. It is thought that every sheet of rubber means a 

 sheet of blotting paper of the same size. This is not so, as every sheet of 

 blotter will coagulate, eight, ten, or even more sheets of rubber before it is 

 used up. It must be remembered that there are two processes in dry coagulation. 

 First the surplus water drains off and the globules are left ; each globule con- 

 tains water which must be got rid of before coagulation takes place unless the 

 albumins are coagulated, when it becomes a wet coagulation. The blotter will 

 not soak up this water in the globule, but it can be gob rid of by slow drying 

 in the air or by artificial heat of the sun's rays. In the case of a porous tile 

 the water is apparently soaked out of the globule immediately the rubber 

 coagulates. I have not examined this* rubber microscopically, and cannot be 

 sure that the globules are free from water. Pressure will also take away the 

 water from the globules. Pressing between two blotters makes good rubber, 

 and pressing between two porcelain tiles still better, because the tile is more 

 durable. Another pressure method is to hang the latex up in a cloth bag, 

 allowing all the surplus water to drain off, and then to exert pressure on the 

 outside of the bag. This would not make uniform rubber, and it would be 

 likely to be thick. The objection to blotting paper has been that the paper 

 adheres to the rubber. Most of this can be scrubbed off with a brush, but 

 this necessitates a good deal of labour. However, very little rubber will come off 

 on the paper if it is watched carefully and taken off at the right moment. 



COAGULATION BY CHEMICALS AND HEAT. 



Wet coagulations are of two sorts : coagulation by chemicals, and coagu- 

 lation by physical forces, such as heat. In the last category there is only one 

 certain way that I know of, that of boiling. Coagulation by the boiling 

 takes place differently at different times. Sometimes the latex coagulates before 

 reaching the boiling point, and at other times not until the water is half boiled 

 away. What makes this difference I do not know. Boiled rubber is full of 

 moisture, is irregular in shape, and appears to me to be weaker than other 

 rubbers. It appears tnat the more boiling necessary, the weaker the rubber. I 

 have not been able to coagulate by simply adding boiling water to the latex 

 and leaving it to stand, as Dr. Weber recommended. The coagulation of latex 

 before it is thoroughly washed is probably a heat coagulation. It is possible 

 that cold, vacuum, electricity, etc., might be outside influences that could affect 

 coagulation. 



Coagulation by chemicals has some drawbacks. Most chemicals 

 appear to weaken rubber. Chemicals are likely to be costly, and many chemical 

 coagulations are uncertain, and depend on other conditions, such as temperature, 

 age of latex, etc. Latex which has been a day or two out of the trees will 

 coagulate by chemicals much more more quickly than fresh latex. 



Alcohol, of all chemicals I have used, makes the strongest rubber, and 

 coagulates the most quickly. It appears to have no other action, and to produce 

 no colour change on the latex or black water. The objection to alcohol is the 

 expense, as the duty on it is heavy. The preparation known as sulpho-naphthol 

 is a quick coagulant, but it takes some quantity of it to coagulate, and it makes 



