692 CAOUTCHOUC 



friend, he records the localities, trees, tools, and details for obtaining the sap, and 

 forming articles. 



M. do la Condamine concludes his remarks upon the memoir of M. Fresneau with 

 words of sufficient import, and indeed -with prophetic spirit, and says, ' it Trill be an 

 exclusive object of commerce for that colony -which possesses this species of treasure." 

 MM. Herissent and Macquer in 1761, gave their chemical observations to the Aca- 

 demic Eoyale on caoutchouc, or elastic resin of Cayenne. They refer to the softening 

 and solution by oils and heat, ' but the caoutchouc does not again takes its solidity or 

 elasticity.' By rectifying oil of turpentine upon lime and dissolving caoutchouc in it, 

 they obtained a pasty mass -which allowed the caoutchouc to regain its former elastic 

 state. They point out that ether may be advantageously used, and they complain of 

 the great expense of Dippel's animal oil as a solvent. While pointing out the surgical 

 uses of caoutchouc, Macquer describes the necessity for carefully rectifying the ether, 

 taking 8 or 10 pounds, and only receiving the first 2 pounds for the solution of caout- 

 chouc. He used, instead of clay, moulds of -wax, held by pincers, and plunged in the 

 ethereal solution, and by repeated coatings, allo-wing the ether to evaporate, a thin 

 covering -was obtained ; by the heat of boiling -water the -wax flowed out, and a tube 

 of caoutchouc remained. He states that he found it difficult to get the tubes uniform. 

 M. Grossart in 1 768, published his experiments on preparing tubes of India-rubber 

 by means of ether and boiling -water : these memoirs seem to have remained -without 

 sufficient reference and study. 



It has been received as an opinion in England and America, that one of the earliest 

 notices of the useful properties of India-rubber is that given by Dr. Priestley, in a 

 work evidently got up -with great care, called, ' A Familiar Introduction to the Theory 

 and Practice of Perspective, by Joseph Priestley, LL.D., London, 1770.' At the end 

 of the preface is the folio-wing addition : ' Since this work -was printed off, I have seen 

 a substance excellently adapted to the purpose of -wiping from paper the marks of a 

 black-lead pencil. It must, therefore, be of singular use to those -who practise drawing. 

 It is sold by Mr. Nairne, Mathematical Instrument-maker, opposite the Eoyal Exchange. 

 He sells a cubical piece of about half an inch for three shillings, and he says it will 

 last several years.' 



It will bo remarked that no name for the substance is mentioned ; the preface is 

 dedicated 'to Sir Joshua Eeynolds, Knt., F.E.S., Leeds, March 20th, 1770;' and we 

 may fairly conclude that the substance was at this time a novelty in art and trade. 



It seems probable, that the experiments with balloons, and the application of air- 

 tight varnishes, especially those by Messrs. Charles and Eobert, called more general 

 attention to the properties of India-rubber in Europe. 



Mr. Hancock says, ' This substance came first into notice about the beginning of 

 the last century, moulded into the shapes of bottles and animals. It was sold as high 

 as a guinea the ounce, and used for rubbing out pencil-marks ; but scarcely anything 

 was known of its history, except that it came from America.' 



The juice itself has been of late years imported. It is of a pale yellow colour, and 

 has the consistence of cream. It becomes covered in the bottles containing it with a 

 pellicle of concrete caoutchouc. Its specific gravity is 1'012. When it is dried it loses 

 55 per cent, of its weight ; the residuary 45 is elastic-gum. When the juice is heated 

 it immediately coagulates, in virtue of its albumen, and the elastic-gum rises to the 

 surface. It mixes with water in any proportion ; and when thus diluted, it coagulates 

 with heat and alcohol as before. 



Hitherto the greater part of the caoutchouc has been imported into Europe from 

 South America, and the best from Para ; but of late years a considerable quantity 

 has been brought from Java, Penang* ( Singapore, Assam, and Africa. Many years 

 ago, Mr. William Griffith published an interesting report upon the Ficus clastica, 

 the caoutchouc tree of Assam, which he drew up at the request of Captain Jenkins, 

 agent in that country to the Governor-General of India. This remarkable species of 

 fig-tree is either solitary or in twofold or threefold groups. It is larger and more 

 umbrageous than any of the other trees in the extensive forest where it abounds, and 

 may be distinguished from the other trees at a distance of several miles, by the 

 picturesque appearance produced by its dense, huge, and lofty crown. The main 

 trunk of one was carefully measured, and was found to have a circumference of no 

 less than 74 feet ; while the girth of the main trunk along with the supports imme- 

 diately round it, was 120 feet. The area covered by the expanded branches had a 

 circumference of 610 feet. The height of the central tree was 100 feet. 



It has been estimated, after an accurate survey, that there are 43,240 such noble 

 trees within a length of 30 miles and a breadth of 8 miles of forest, near Ferozepore, 

 in the district of Chardwar, in Assam. 



Lieutenant Veitch has since discovered that the Ficus clastica is equally abundant in 

 the district of Naudwar. Its geographical range in Assam seems to be between 



