426 LATEX 



dry. In this way ' ball ' Para rubber is obtained. Sometimes a paddle 

 which may be dipped into the latex, is used instead of a pole and the 

 rubber removed by splitting it along one side ; this gives ' spade,' 

 ' paddle,' or ' biscuit ' Para rubber. Para rubber, therefore, consists 

 of the latex dried after coagulation, and contains in addition to 

 caoutchouc all the other constituents of the latex (except water). 

 The coagulation is probably due to precipitation of part of the 

 albumin by the acetic acid of the smoke. The latex contains about 

 40 per cent, of caoutchouc, 2-8 per cent, of proteids, and 55 per cent, 

 of water. 



Description. Para rubber occurs in commerce in elastic, rounded, 

 cylindrical, or flattened masses of varying size and shape, and of 

 characteristic odour. Externally they are of a uniform brownish 

 black colour, but internally they exhibit under a lens a large number 

 of very thin yellowish layers separated by dark lines, each layer 

 representing a coat of coagulated latex. The drug is insoluble in 

 water, alkalies, or dilute acid, but chloroform, oil of turpentine, 

 carbon bisulphide, and benzene make it swell and become soft and 

 gelatinous, the caoutchouc dissolving and leaving a gelatinous sub- 

 stance undissolved. Digestion with alcohol removes from Para 

 rubber about 1*5 per cent, of resin, but inferior rubbers may yield 

 much more. 



Constituents. Para rubber contains from 40 to 60 per cent, of 

 the hydrocarbon caoutchouc (caoutchouc-gutta) which when quite 

 pure is white and corresponds in composition to the empirical for- 

 mula (C 10 H 16 ) n ; it is a very unstable body and rapidly oxidises. In 

 Para rubber it is associated with 30 to 50 per cent, of the gelatinous 

 substance which probably protects the caoutchouc from change ; 

 small quantities of resin, fat, colouring and mineral matter are also 

 present. Good rubber always contains a considerable amount of the 

 gelatinous substance and only small quantities of resin, &c. ; in poor 

 rubbers the reverse is the case. 



Varieties. Ceylon or Plantation Rubber. This now forms a very 

 important commercial article, the production of which is rapidly 

 increasing. The latex is coagulated by allowing it to stand for a 

 few hours, with or without the addition of a little acid, and the 

 coagulum is put into a washing-machine consisting of a pair of very 

 heavy corrugated cylinders over which water is poured. The rubber 

 globules are united by this treatment and come from the machine 

 in the form of .thin, crinkled sheets (crepe rubber) which are hung up 

 to dry. Sometimes the coagulum is passed through a machine which 

 presses the rubber into small vermiform pieces ; these are afterwards 

 submitted to heavy pressure which converts them into ' block ' 

 rubber. Such rubber is of course free from the proteids and other 



