1886.] on Becent Progress in the Coal-tar Industry. 451 



to several millions sterling, whilst tlic industries based upon these 

 results give employment to thousands of men. 



Sources of the Coal-tar products. — In 'order to obtain these products, 

 whether colours, perfumes, antipyretic medicines, or sweet principle, a 

 certain class of raw material is needed, for it is as impossible to get 

 nutriment from a stone as to procure these products from wrong 

 sources. All organic compounds can be traced back to certain hydro- 

 carbons, which may be said to form the skeletons of the compounds, 

 and these hydrocarbons are divisible into two great classes : (1) the 

 paraffinoid, and (2) the benzenoid hydrocarbons. The chemical dif- 

 ferences both in properties and constitution between these two series 

 are well marked. One is the foundation of the fats, whilst the other 

 class gives rise to the essences or aromatic bodies. Now all the 

 colours, finer perfumes, and antipyretic medicines referred to, are 

 members of the latter of these two classes. Hence if we wish to 

 construct these complicated structures, we must employ building 

 materials which are capable of being cemented into a coherent edifice, 

 and therefore we must start with hydrocarbons belonging to the 

 benzenoid series, as any attemjDt to build up the colours directly 

 from paraffin compounds would prove impracticable. Of all the 

 sources of hydrocarbons, by far the largest is the natural petroleum 

 oils. But these consist almost entirely of paraffins, and hence 

 this source is commercially inapplicable for the production of 

 colours. We have, however, in coal itself, a raw material which by 

 suitable treatment may be made to yield oils of a valuable character. 

 Of these treatments, that followed out in the process of gas-making is 

 the most important, for in addition to illuminating gas in abundant 

 supply, tar is produced which contains principally that benzenoid 

 class of substances already referred to, and which, to use the words 

 of Hofmann, " is one of the most wonderful productions in the whole 

 range of chemistry." The production of these latter as distinguished 

 from the paraffinoid group appears to dejDcnd upon a high temperature 

 being employed, to effect the necessary decomposition. 



The quantity of coal made into coke for use in the blast furnace 

 is larger than that distilled for gas-making, no less than between eleven 

 and twelve million tons of coal being annually consumed in the blast 

 furnaces of this country in the form of coke, and capable of yielding 

 two million tons of volatile products. Uy) to recent times, however, the 

 whole of these volatile products has been burnt and lost in the coke 

 ovens. But lately, various processes have been devised for preventing 

 this loss, and for obtaining the oils, which might be made available 

 as colour-producing materials. It is, moreover, a somewhat remark- 

 able fact that only in one or two cases have the conditions been 

 complied with which render it possible to obtain the necessary 

 benzenoid substances. In the ordinary coking ovens, as well as in 

 the blast furnaces, although the temperature ultimately reached is far 

 in excess of that needed to form the colour-giving hydrocarbons, yet 

 the heating process is carried on so gradually that the volatile pro- 



