498 FETCH : 



when the flow was small. The latex was then strained 

 through coarse cloth, and coagulation effected in fixed quan- 

 tities. This was an important advance, though it is now so 

 generally adopted that no one realizes that it only came into 

 use in 1899. No mention was made of coagulating in other 

 than collecting cups in other reports, until Curtis referred to 

 pouring the latex into plates in his report for 1899, after his 

 visit to Ceylon. 



Parkin's chief work, however, was concerned with coagula- 

 tion. He experimented with a dozen different coagulaYits and 

 determined the limit of coagulation for each, finally selecting 

 acetic acid because it effected complete coagulation over the 

 widest range. Samples of the rubber prejDared were analysed 

 and tested by MM. Michelin & Cie., and formed the first set 

 of specimens submitted to comparative tests of this kind. 

 The results of these tests were published in the Annals of the 

 Royal Botanic Gardens, Peradeniya, and have been generally 

 overlooked by writers on the subject. The method he 

 recommended was as follows : — The latex was filtered through 

 coarse cloth and then diluted ; next it was heated nearly to 

 boiling point, and the requisite amount of acetic acid with a 

 little creasote added ; after the separation of the rubber, cold 

 water was added. The white spongy mass of rubber was then 

 pressed into thin sheets, in order to obtain rapid drying 

 throughout the mass. Parkin stated that acetic acid effected 

 coagulation equally well in the cold, and that that method 

 might prove the better for use on a large scale, but it was 

 dilfi(!ult to use creosote in the cold. He noted that " tacki- 

 ness " was produced by drying in the sun, and advised 

 quicklime or calcium chloride for rapid drying. 



The value of this ])art of Parkin's work may be gauged from 

 the fact that the chief ])oints of his method have been univer- 

 sally adopted. The " cold " method has proved most suitable, 

 and consequently creosote has been omitted, but a few years 

 ago heating the latex was re-introduced in order to obtain 

 pale rubber. The methods previously in vogue by which 

 small masses of rubber coagulated naturally in the collecting 

 cups were allowed to putrefy or dry in the sun were obviously 

 impracticable for ukc ou a large scale, and Parkin's method 



