356 CHEMICAL DISCOVERY AND INVENTION 



camphor has been the subject of several patents, and for a time 

 synthetic camphor was found in the European markets, but has 

 disappeared again in consequence of a reduction of price in the 

 Japanese product. 



The history of essential oils would not be complete without at 

 least a passing reference to the extensive class of hydrocarbons 

 called terpenes. The most prominent and abundant of these 

 compounds are the two pinenes which are the chief constituents 

 of the oil or spirit of turpentine. The one obtained from the 

 United States is known as American or as English turpentine, 

 and is obtained by distillation from the resinous exudation from 

 the Pinus australis and Pinus Tceda. It rotates the polarised 

 ray to the right. French turpentine is a similar product from 

 Pinus maritima, but is Isevorotatory. Spirit of turpentine is 

 familiar enough as a colourless inflammable liquid with a peculiar 

 smell. It is consumed in large quantity as a solvent and diluent 

 in common paint, and some varnishes. It is also used as an 

 external application in rheumatism and other disorders in which 

 a stimulant is required. 



The terpenes have been the subject of investigation in the 

 hands of many chemists, but their constitution is now completely 

 understood, and several of them have been produced synthetically 

 since the beginning of this century. 



A complete account of the chemistry of the terpenes will be 

 found in a course of five lectures given in 1912 before the Pharma- 

 ceutical Society of Great Britain, by Sir William Tilden, Professor 

 W. H. Perkin, and Mr. J. C. Umney. 



CHAPTER XXIV 



VEGETABLE FIBRE AND PRODUCTS FROM CELLULOSE 



ALL plants in the earliest stages or most primitive forms are 

 composed of cells, that is minute membranous bags spheroidal in 

 form, and having no mouth or opening. As the plant reaches a 

 more advanced stage of development these cells change in form, 

 many assuming elongated shapes, becoming tubes often with 

 tapering extremities. All the vegetation which clothes the 

 surface of the earth consists therefore of a mixture of such 

 minute hollow elements, which closely packed together form the 



