1862.] on Mauve and Magenta, 469 



is the manufacture of coal-gas ; but this is so well known as not to 

 need any detailed description. Let me briefly remind you of the 

 principal features of the distillation of coal, by directing your 

 attention to the two large diagrams representing the " retort house " 

 and the " condensers " of a gas-work. You observe how the coal is 

 heated in stupendous retorts, five or seven of which are generally 

 associated in one furnace. The gas ascends from these retorts in 

 vertical tubes, the bent ends of which dip into a large horizontal pipe, 

 partly filled with water, called the hydraulic main, a considerable 

 amount of the oily and tarry substances generated with the gas being 

 separated by the water. The gas, so far purified, passes on through the 

 condensers — immense vertical iron pipes constantly cooled by a cur- 

 rent of cold water which surrounds their external surface. In these 

 condensers an additional quantity of oily matter is separated, which, 

 together with the oily substances deposited by the gas daring its pas- 

 sage through the hydraulic main, is collected in appropriately placed 

 cisterns. The gas, having traversed the condensers, passes through 

 a series of further purifications before it is delivered into the mains of 

 our streets ; but these, unconnected as they are with our subject, must 

 no longer occupy our attention. 



The distillation of coal being the fundamental operation in the 

 manufacture of Mauve and Magenta, it is but fair that it should 

 not remain without an experimental illustration. In this tubulated 

 retort of hard glass, I am heating fragments of coal. The beak of 

 the retort is inserted into a three-necked glass globe, the lower 

 neck of which terminates in a tube, communicating with a glass vessel 

 for the collection of the " oily products ;" while the third neck is pro- 

 vided with a delivery-tube for the discharge of the gas, which finds its 

 way into a glass gas-holder. The coal has been heated only for a few 

 minutes, and the gas already begins to be freely evolved ; already I 

 may light it at the orifice of the delivery-tube, which, for this purpose, 

 I have removed from the gas-holder; already it burns with the cha- 

 racteristic luminous flame of coal-gas. In the meanwhile, you observe, 

 a considerable quantity of the " oily products " has accumulated in the 

 receiver. Their formation continues as long as the gas is evolved. 

 Ultimately the coal is entirely resolved into gas and oily products, a 

 non-volatile residue, the cohe, remaining behind in the retort. 



It is in the oily products, the so-called " coal-tar-oil,'* that our 

 interest is centred. To my mind this coal-tar-oil * is one of the most 

 wonderful productions in the whole range of chemistry. That may be 

 rather a one-sided view, but having in younger years spent much time 

 in the investigation of this substance, I have acquired quite an affection 

 for it. Nor can you fail to appreciate the interest which coal-tar 

 presents to the chemist when you look at the diagram in which I have 

 endeavoured to arrange synoptically the various substances which have 

 been eliminated from it. 



* A large specimen of coal-tar-oil was here exhibited. 



