304 CHEMICAL DISCOVERY AND INVENTION 



"At present there are 8297 by-product coke ovens built in 

 this country, of which 6678 are fitted with benzol recovery 

 arrangements, capable of producing something like 10 million 

 tons of coke per annum. 



'' The yields of the various by-products obtainable on such 

 coke oven installations naturally vary with the locality and 

 character of the coal seam ; but they probably average some- 

 what as follows expressed as percentages on dry coal car- 

 bonised : 



Or, to put the matter a little differently, each ton of dry coal 

 carbonized yields from 20 to 35 Ibs. of ammonium sulphate, 

 from 56 to 112 Ibs. of tar, and from 2 to 3J gallons of crude 

 benzol, etc., according to the locality. About 65 to 70 per cent 

 of the crude benzol is obtained as finished products benzene, 

 toluene, solvent and heavy naphthas. 



" How rapid has been the development of the by-product 

 coking industry in this country during recent years may be 

 judged from the following official returns of the quantities of 

 ammonium sulphate annually made by such plants, as compared 

 with the corresponding quantities produced in gas works. 



Tons of Ammonium Sulphate Produced in 



By ^ d ptS. ke - <***. 



1903 .... 17,435 ... 149,489 



1908 .... 64,227 ... 165,218 



1913 .... 133,816 ... 182,180 



" In the natural course of events the final disappearance of 

 the wasteful beehive coking oven from this country is now only 

 a matter of a few years ; but I venture to suggest that public 



