65 



THE PRESIDENT'S ADDRESS. 



BY-PRODUCTS OF ORGANIC EVOLUTION. 



By Prof. Arthur Dendy, D.Sc, F.R.S. 



{Delivered February 25th, 1913.) 



Plate 7. 



We are all familiar with the fact that in the manufacture 



of any particular product of human industry the raw material 



employed is rarely entirely used up, a more or less considerable 



* 



residue generally remaining over after the process is completed. 

 In so far as the prime object of the manufacturer is to produce 

 some one special product, the residue which cannot be employed 

 for this purpose must be regarded as waste. It frequently 

 happens that this waste product is a highly deleterious substance, 

 the difficulty in the disposal of which may constitute a very 

 serious obstacle to the successful prosecution of the industry in 

 question. On the other hand, it also frequently happens that 

 what were primarily waste products may prove to have a value 

 of their own quite apart from the main object at which the 

 manufacturer is aiming. They then cease to be merely waste 

 products and become valuable by-products, perhaps even more 

 valuable than the main product itself. 



Thus in the distillation of coal in a gasworks the main purpose, 

 that for which the machinery and apparatus are primarily 

 intended, is the production of gas, but coke and tar and other 

 by-products are also produced, all of which are now, I suppose, 

 applied to some useful purpose, and thus have a value of their 

 own. Indeed the existence of coal-tar has given rise to a whole 

 series of new industries, involving the production of almost endless 

 substances, such as the wonderful aniline dyes and so forth, 

 which many people will regard as far more valuable and desirable 



Jourx. Q. M. C, Series II. No. 72. 5 



