10 Guayule. 



An alternative treatment consists in allowing the washed rubber 

 from the first skimming-tank following the pebble-mill to soak for a week 

 in settling-tanks, during which time the bagasse becomes water-logged 

 and sinks. The soaking is probably of value also in separating from the 

 rubber certain substances, probably enzymatic in character, which other- 

 wise would contribute to the earlier breaking down of the rubber. 



The clean rubber is now passed between corrugated and smooth 

 rolls for the purpose of washing and sheeting (plate 3, fig. C), when the 

 product is ready to be put on the market. Unless further treatment 

 ensues, the rubber thus prepared contains about 25 per cent moisture, 

 together with a proportion of resin. 1 



Other special steps in treatment are applied to the separation of 

 rubber from bagasse, or in preparing special grades. For example, 

 boiling the skimmed rubber in a 1 to 2 per cent solution of caustic soda 

 has been used as an aid in the separation of rubber and fiber, and for 

 partial deresination by the saponification of the resin acids. By this 

 means the amount of resin, 25 per cent, usually present, may be reduced 

 to 17 or 18 per cent. 2 Other modifications in treatment are necessitated 

 by the condition of the plants when treatment is begun. Old, weathered 

 and dried-out shrub is not worked with the same ease nor with the same 

 result as fresh, while a certain amount of seasoning is an advantage. Con- 

 siderable losses have been entailed by storing guayule in the yard exposed 

 to the sun (plate 4, fig. A), as may be imagined if a million dollars' worth 

 of shrub is handled in this way, even though the amount of deterioration 

 is small. This loss is now avoided by placing the shrub in storehouses. 



THE NATURAL SUPPLY OF SHRUB. 



With such large interests at stake, it soon became a matter of 

 moment to determine the relation of supply of the shrub to the manu- 

 facture, as to total supply in sight, as to its rate of reproduction under 

 natural conditions, and as to the possibility of its cultivation. 



The first of these questions was naturally the first to be raised, and 

 many attempts have presumably been made to find an answer. The 

 earliest, and, so far as I am aware, the only published calculation was made 

 by Endlich (loc. cit.), who assumed an average amount of half a ton per 

 hectare in virgin fields. The total area of the general guayule region 

 being taken as 75,000 square kilometers, and assuming that only one- 

 tenth of this carries the shrub, Endlich arrived at the sum of 375,000 

 tons total supply in Mexico, which, at the rate of 7 to 10 per cent of 

 rubber, represents 26,250 to 37,500 tons of rubber. This estimate was 

 probably quite conservative, as indicated by calculations based upon 

 official reports brought together in the India Rubber World. 



Using the probable corrections for exports of crude rubber other 

 than guayule, this publication gives the total imports of guayule rubber 



1 Whittelsey, 1909. 



2 At this writing an announcement is made (Guayule Rubber by a New Proc- 

 ess, India Rubber World, December, 1909) that a method ("physico-mechanical" 

 sic.) has been patented whereby crude rubber, after treatment, has the com- 

 position: "Pure caoutchouc, 88 per cent; resin, 7 per cent; water, 5 per cent." 



