114 Chemical Manufactures. 



by rendering the earthy bases soluble,, and therefore capable of 

 removal. The subsequent addition of lime neutralizes the re- 

 sinous colouring matters and other hurtful substances which 

 the acid may have set free. When sulphuric acid is added to 

 ground madder, all that is soluble in water can be extracted — 

 including* a large quantity of sugar, which is used for the ma- 

 nufacture of a spirit that pays for the whole process ; since, 

 though it is not drinkable, it answers well for varnishes. The 

 dye stuff obtained in this way is termed garancine ; it gives no 

 colour to cold water ; but, as it produces its whole dyeing effect 

 at once, it is more powerful than the original madder ; it affords 

 brighter colours also, and does not stain the white parts of the 

 cloth, which greatly simplifies the after-process. But, as the 

 colours which it produces are less permanent, and do not so 

 effectually, resist soap, etc., it cannot be so well employed for 

 pink or purple. When the residue, after dyeing with madder, 

 and the exhausted dye-liquor, are acted on with sulphuric acid, 

 an inferior garancine, termed garanceux, is obtained; it will 

 not give a good purple. The chief derivatives of madder, may 

 be seen among the chemical products in the eastern annex. 



But by far the most interesting manufacture connected with 

 dyeing, is that which has for its object the production of 

 colouring matters from coal-tar. The latter was long a re- 

 proach, both to the chemist and the economist, neither of whom, 

 until within a recent period, applied it to any very useful pur- 

 pose. It was generally consumed as fuel, the least profitable 

 way in which it could be employed. Very valuable substances 

 are however, now obtained from it, and among them aniline, 

 which, with its compounds, has a special interest, on account 

 of its capabilities as a source of colour, having been discovered 

 long since the Exhibition of 1851. It is one of the bases dis- 

 covered by Bunge, and was called by him Kyanol, but it has 

 since been termed aniline, from the Indian name for one of the 

 plants whence indigo, the substance from which it was first 

 obtained, is procured. It may be had from a variety of sources, 

 bat most abundantly from coal-tar. 



In the method of manufacture that is found most inex- 

 pensive and convenient, naphtha is first obtained by distillation 

 of the tar; then benzole, by distillation of the naphtha, with 

 certain precautions; nitro-benzole, by the addition of nitric 

 acid to the benzole ; and aniline from the nitro-benzole, by 

 means of reducing agents. Two gallons of tar produce about 

 ten grains of aniline. The various stages of this process are 

 beautifully illustrated (No. 581) by the Messrs. Perkins, who 

 exhibit also a mass of aniline purple, in the solid form, which 

 is believed to have required for its production the tar from two 

 thousand tons of coal ; but it would impart a fine purple to one 



