616 TRANSACTIONS OF SECTION B. 



gum arabic are at present chiefly derived from the French Colony of Senegal, 

 ft iy, however, clear from the examination of gum collected in West Africa 

 that that country, and especially Northern Nigeria, will be able in the future to 

 contribute to the needs of the British manufacturer, in addition to the Sudan, 

 India, and Australia, which will also be able to make important contributions. 

 In connection with the investigation of these gums derived from new sources 

 at the Imperial Institute, the very remarkable observation has been made that 

 certain gums from India and the Colonies possess the property of evolving acetic 

 acid when exposed to the air. The chemical constitution of one of these gums 

 has been fully investigated at the Imperial Institute by Mr. H. H. Robinson, 

 who will contribute a paper on the subject to the Section, in which he will show 

 that the production of acetic acid is due to the elimination of an acetyl group by 

 hydrolysis through the moisture of the air. He has also succeeded in elucidating 

 to a large extent the chemical nature of the gum. Mr. Robinson will also make a 

 report on the present position of the chemistry of gums, a class of substances 

 whose constitution is exceptionally difficult to unravel. Little, if any, advance 

 has been made in recent years on the well-known researches of O'SuUivan. 



There is no more important group of questions demanding attention from the 

 chemist at the present time than those connected with the production of indiarubber 

 or caoutchouc. An enormous increase in the demand for indiarubber has taken place 

 in the last few years, and last year the production was not less than 60,000 tons. 

 Until recently the supply of rubber came chiefly from two sources — the forests of 

 Brazil, which contain the tree known as Ilevea brasiliensis, furnishing the Para 

 rubber of commerce which commands the highest price, and the forests of Africa, 

 where climbing plants, generally of the Landolphia class, also furnish rubber. The 

 increased demand for caoutchouc has led to the extensive planting of the Para 

 rubber tree, especially in Ceylon and in the Federated Malay States. Systematic 

 cultivation and improved methods of preparation are responsible for the fact that 

 the product of the cultivated tree, which begins to furnish satisfactory rubber 

 when six or seven years old, is now commanding a higher price than the product 

 of the wild tree in Brazil. It is estimated that within the next seven years the 

 exports of cultivated indiarubber from Ceylon and the Federated Malay States 

 will reach between ten and fifteen million pounds annually, and that after fifteen 

 years they may exceed the exports of the so-called wild rubber from Brazil. 



The services which chemistry can render to the elucidation of the problems of 

 rubber production and utilisation are very numerous. Methods of treatment 

 depending on a knowledge of the other constituents of the latex have led to the 

 production of rubber in a purer condition. Much still remains to be elucidated 

 by chemical means as to the nature of the remarkable coagulation of the latex. 

 As is well Icnown, the latex is a watery fluid resembling milk in appearance 

 which contains the rubber, or, as I think more probable, the immediate precursor 

 of rubber, together with proteids and other minor constituents. The constituent 

 furnishing rubber is in suspension, and rises like cream when the latex is at rest. 

 On the addition of an acid, or sometimes of alkali, or even on mere exposure, 

 coagulation takes place and the rubber separates as a solid, the other con- 

 stituents for the most part remaining dissolved in the aqueous liquid or ' serum.' 

 The first view taken of the nature of the coagulation process was that, like the 

 coagulation of milk by acids, it is dependent upon a process of proteid coagula- 

 tion, the separated proteids carrying down the rubber during precipitation. 



This explanation cannot, however, be considered complete by the chemist, and 

 there are peculiarities connected with the coagulation of the latex which are 

 opposed to the view that it is wholly explained by the coagulation of the 

 associated proteids. The experimental investigation of the question on the 

 chemical side is beset with many difficulties which are increased if access 

 cannot be had to fresh latex. A number of experiments were made at the 

 Imperial Institute with latex forwarded from India. The difficulties contended 

 with in preventing coagulation during transit were great, but in the case of the 

 latex derived from certain plants these were to some extent surmounted, and tho 

 results obtained, especially with reference to the behaviour of certain solvents 



