April 1907. ] 



19? 



Saps and Exudations. 



laticiferous system. The latex is apparently contained in isolated cells which ar 

 piesent in both wood and bark, though principally in the latter. The bark, in fact, 

 furnishes a little more than three-fourths of the total amount of rubber, but it also 

 contains the resinous substances which give rise to the stickiness hitherto character- 

 istic of Guayule rubber. Apparently little or no rubber is present in the young leafy 

 shoots. From the results of practical trials, it is stated that in 100 parts of the 

 dried plants there are on an average 47 parts of wood, iU parts of bark, and 8£ 

 parts of leaves and young shoots. 



Experiments in connection with the extraction of Guayule rubber have been 

 in progress for a number of years, but it is only within the last two years that the 

 matter has attained commercial importance. Only one factory was actually at 

 work in Mexico last year, but several others were in course of erection, and will 

 commence operations at an early date. A number of different processes have been 

 introduced for the extraction of Guayule rubber, some of Avhieh have been kept 

 secret, whilst others have been protected by patents. The methods may be divided 

 into two chief classes : (1) those in which the rubber is extracted by solvents, and 

 (2) those in which it is separated by mechanical means. In processes of the first kind 

 the plants, after crushing, are treated with a suitable solvent, the greater part of 

 which is afterwards recovered by distillation, and the residue is freed from resin 

 by treatment with a hot alkaline solution, or with wood spirit. In the methods 

 involving mechanical treatment, the plants are reduced to a coarse powder which 

 is submitted to a rubbing or heating action, either in the presence or absence of 

 water, until the particles of rubber cohere and can be separated from the vegetable 

 matter. The rubber thus obtained can be treated as above for the removal of the 

 resin, and is freed from the vegetable impurities by thorough washing with water. 

 In other processes the crushed plants are heated with an alkaline solution in a 

 similar manner to that used for the preparation of wood pulp, and the separated 

 rubber is washed well with water. 



The amount of crude rubber furnished by these processes varies from 8 to 12 

 per cent., according to the amount of moisture present in the plants treated, and 

 the yield of the purified material may be taken as 7 to 10 per cent. 



* Guayule rubber as first prepared was usually in flakes, which had a greenish- 



grey colour when fresh, but blackened on the surface when kept. It was very soft 

 and sticky, OAving to the presence of a large amount of resin, and it frequently 

 contained large proportions of water and vegetable impurities. The com- 

 position of two such specimens has been recorded by Markwald and Frank aa 

 follows 





I. 



11 





Per cent. 



Per cent, 



Ash 



T3 



2-08 



Mechanical impurities 



... 9*7 





Water ... 



26-0 



20 '69 



Resin 



29*2 



19-35 



Caoutchouc 



33-8 



57-28 



The caoutchouc present in these specimens was a little sticky, but exhibited 

 considerable tenacity. 



The introduction of improved methods for washing the crude rubber and 

 for removing some of the resin has resulted in the production of a much more 

 superior material. The crude rubber as at present obtained usually contaius about 

 03 per cent, of caoutchouc and 22 per cent, of resin, the remaining 15 per cent, being 



