427 

 OUR COAL-TAR DYES. 



BY WM. PROCTER, M.D., F.C.S. 



It would be an extremely difficult matter to over-estimate the value of 

 chemistry to the various arts and manufactures, neither can the important 

 benefits which it has conferred on society through them be ranked too highly, 

 although the results of such applications may be deficient in the grandeur 

 and sublimity displayed by some others, yet in their usefulness in both great 

 and small matters, in adding to the social comforts or even the luxuries of 

 life, it holds a foremost position, and yields in these respects to no other. 

 This is not the place to consider these advantages in detail, but none are 

 more interesting than the utilization of waste products. A large number of 

 substances, often vast in quantity, are the secondary results of many manu- 

 factures, which were formerly rejected as perfectly useless, or were even de- 

 structive to the neighbourhood in which they were generated. A large 

 amount of these residues are at the present time, by improved processes, no 

 longer wasted or injurious, but are made available for useful purposes, 

 being often as valuable as the primary object of the manufacture. 

 Numerous illustrations in support of this statement might readily be ad- 

 duced. One example is sufficient, and is more remarkably exemplified in 

 none than in the manufacture of coal gas ; at one time gas alone was ob- 

 tained, and the gas liquor and tar were rejected as useless, but now the 

 illuminating fluid is obtained free of cost, the secondary products, formerly 

 wasted, yielding a profit sufficient to defray the expenses of the works — What 

 are they ? Ammonia, Naphtha, Benzole, and Paraffin have numerous uses. 

 Tar, which, in addition to other applications, furnishes by the magic of 

 Chemistry, colours which rival the most brilliant of our dyes, and even the 

 Lime used for purification forms a useful agricultural manure, and leaving 

 finally the valuable fuel coke as a residue. 



Our illuminating gas, it is well known, is attained by submitting coal to 

 heat in closed iron vessels. This is what Chemists call destructive dis- 

 tillation, and under these circumstances the elements of the coal rearrange 

 themselves to form a series of new and complete compounds whose name is 

 legion. Dr. Hofmann enumerates no less than forty-five different substances 

 as the result of the process. 



Leaving out of consideration for the present these products, it may be 

 stated, generally, that besides the residue, coke, first, volatile gases, and 

 secondly, a liquid tar are the results of the distillation of coal, and it is- 

 to the latter, which is collected in proper cisterns, that attention is now to 

 be drawn ; the material from which colours vieing in beauty with our finest 

 crimson, purple, and blue are produced. To the consideration of their 

 preparation this paper is to be directed. After the tar is separated from 

 tbe water which exists with it in the gas works, it is submitted to distilla- 

 tion, the result is that a light (Sp. gr. 0.830) and heavy (Sp. gr. 0.885) oil 

 passes over into the receiver, and a black substance known as pitch is left 

 in the retort. Some more detailed knowledge of the constitution of tar 



