THE PRODUCTS OF THE DISTILLATION OP COAL. 297 



so small, that the burning properties are not interfered with by the in- 

 troduction of a large quantity of incombustible materials found to be 

 required with wax, &c. The coloured candles tinted, red, mauve, violet, 

 crimson, &c, by the coal-tar dyes, and produced by the Messrs. Field 

 in various designs, are really beautiful objects. The temperature at 

 which this substance becomes fluid varies with the source from which it 

 is obtained; that from Boghead coal fuses at 114°, that from Bitumen 

 at 110°, whilst the paraffine from Rangoon tar requires a heat of 140° 

 before it melts. A high melting point is an important matter in candle 

 making ; for under such circumstances the well which is formed at the base 

 of the wick during burning, containing a supply of liquid matter ready to be 

 drawn up by the wick for combustion, is preserved intact, and " gutter- 

 ing " obviated. Paraffine candles burn with a clear, white, smokeless 

 flame. According to Dr. Letheby, weight for weight, the illuminating 

 power is 22 per cent, greater than sperm, 40 per ent. greater than wax, 

 46 per cent, greater than stearine, and 58 per cent, greater than compo- 

 site ; or to estimate it in another way, the light produced by 98lb. of 

 paraffine is equal to that of 1201b. of sperm, or 1381b. of wax, or 1441b. 

 of stearine, or 1551b. of composite candles. Accirding to Dr. Frankland, 

 the cost of light in relation to other candles is, paraffine, 3s. 10d.;_ sperm 

 6s.8d.; wax, 7s. 2d. Paraffine is now extensively used to supply the plac e 

 of sulphur in dipping matches, thus remedying the suffocating odour 

 produced by the formation of sulphurous acid when a lucifer is ignited. 

 After the separation of these important substances with such manifold 

 applications and uses, Pitch is left as a residuum, but not as a waste 

 product. A comparatively recent application of it is, the conversion of 

 small, almost valueless, coal into an excellent kind of coke. The pitch 

 is ground and mixed with seven or eight parts of coal, and put into a 

 cokeing oven, the vapour of the pitch becoming decomposed, deposits its 

 carbon on the coke in the process of burning, which increases greatly 

 the product from a given quantity of coal. A manufacture of patent 

 fuel from pitch is also carried on largely near the coal beds of Wales, by 

 grinding and mixing it with small coal, heating together, and then by 

 great pressure moulding it into bricks, when a compact mass is formed 

 in some respects superior to coal. The other applications of pitch con- 

 sist in its use for asphalting roads and roofs ; it is also employed in ship- 

 building and in the preparation of lamp-black. 



Such, then, are the most important points in the technology of the 

 destructive distillation of coal, and few subjects are more extensive or 

 more interesting. Abstruse scientific researches have given these valu- 

 able products to us, and made known and developed their wide applica- 

 tion. The labours of Dr. Faraday into the nature of benzole may be 

 looked upon as the starting point, and the further development is due 

 to the industry of chemists of our own time. There is doubtless yet a 

 mine of wealth to be explored, both in a scientific and commercial sense, 

 capable of producing results probably as little expected, as at first was 

 the appearance of our brilliant but well-known tar dyes. 



VOL. IV B B 



