THE GUAYULE 323 



the milling is complete, which ensues after about 3,000 revolutions at 

 the rate of 30 per minute, the mixture of water, comminuted shrub and 

 bagasse is discharged and flows into skimming tanks. In these a por- 

 tion of the bagasse, consisting of fibrous material (bast, wood) and 

 fragments of other cell walls, sinks, while the agglomerated rubber 

 ("worm rubber"), accompanied by a bagasse composed of minute 

 flakes of cork, floats. This floating mixture can now be separated into 

 practically clean worm rubber and rubber-free bagasse by boiling, and 

 then by submitting it to a pressure of about 250 pounds under water, 

 in order to water-log the cork flakes. A further cleansing of the worm 

 rubber flakes takes place in a tank supplied with a paddle wheel, which 

 beats the floating particles and so rids them of adherent particles. 

 After this there remains but the "sheeting," which is accomplished by 

 passing the worm rubber between corrugated steel rollers to form 

 sheets. It may be packed in sacks in this form or pressed into solid 

 blocks, say, of 50 pounds weight and packed in boxes. In this process 

 it is evident that there are two critical phases, first the agglomeration 

 of the rubber and, secondly, its later separation from the bagasse. The 

 former is relatively easy or difficult, according to the richness of the 

 tissues in rubber, or stated otherwise in the size of the rubber particles 

 within the cells of the tissue. The separation of rubber from bagasse 

 depends on the difference in their specific gravity, using this term in a 

 loose sense. The fibrous elements, namely wood, bast and broken open 

 cell walls, are easily waterlogged — that is, the occluded air is easily dis- 

 pelled, while the cork is difficult to break up and even more so to rob 

 of its air. 



The coarse worm rubber floats rather readily; but the smaller the 

 particles the more slowly they rise to the surface. Any means which 

 may be used to cause a swelling of the particles, or to lessen the dis- 

 tance which they must travel to reach the surface, afford help in attain- 

 ing to segregation of the rubber. The colloidal properties of rubber 

 make swelling possible by means of any of its solvents. The depths of 

 the tanks which are used for separation of rubber and bagasse is obvi- 

 ously important. When it is known that an extraction of 7 per cent, 

 rubber (of which the moisture amounted to 25' per cent.) was raised 

 during about five years to 15 per cent, by slowly improved methods, we 

 may realize the amount of experiment and ingenuity necessarv. It 

 would have been well for the industry to-day if, during the earlier 

 period, there had been less desire to take advantage of the ease of ac- 

 quiring profit and more study and experiment. To be sure, a good 

 deal of rubber left in the bagasse was later reclaimed, but the total lost 

 in spite of this must have amounted to a good deal. This was, how- 

 ever, only one form of economic waste. By far the most serious lay in 

 the method of gathering the shrub by pulling it up by the roots, called, 



