228 ANNUAL OF SCIENTIFIC DISCOVERY. 



traces the various steps 'by which the well-known colors, mauve, 

 magenta, etc., are manufacted from coal-tar: 



Coal-tar is a very complex body. It contains a large number of 

 substances, some of which are volatile, others more difficultly volatile, 

 and others not at all volatile in the ordinary sense of the word. 



I have here a retort filled with tar, and I am now going to pass 

 through that a current of steam; and you will see that after a little 

 while, when it passes through freely, it will distil over along with the 

 water, and that this water will contain, swimming on its top, a certain 

 quantity of naphtha. The steam which passes through the tar will 

 take away the more volatile portions of the tar and condense it upon 

 the top under the name of naphtha. What remains behind is a mix- 

 ture of what is called dead oil and pitch. This dead oil is afterwards 

 distilled off, and what remains behind in the retort is finally pitch. 



In distilling it in this way we obtain from one hundred parts of 

 coal-tar, of naphtha nine parts, of dead oil sixty parts, and of pitch 

 thirty-one parts, so that there are various substances obtained. I 

 have only time, however, to deal with the naphtha. Now, naphtha 

 itself, or the substance which we get over by distilling the tar with 

 steam, is a general word also. The crude naphtha contains, first, 

 basic oils, or oils acting as bases ; secondly, acid oils, or oils acting as 

 acids ; and, thirdly, neutral hydrocarbons. 



This naphtha is purified and clarified. There is added to it sul- 

 phuric acid. The sulphuric acid takes up the basic oils, unites with 

 them and forms salts sulphates of these bases. The sulphuric acid 

 unites with the basic oils and produces this " sludge," as it is termed 

 bv the manufacturers the bases united with the acid. 



i/ 



Now, these are extremely valuable, and it is from them that coal- 

 tar colors are obtained ; but they are entirely lost by the manufac- 

 turer. They will probably be saved afterwards, but at present they 

 are thrown away as a sort of tar. The first things that we obtain of 

 any advantage are the acid oil and the naphtha. The naphtha itself, 

 the crude naphtha, is employed at once, without any purification, for 

 the purpose of making India-rubber water-proof coats and similar 

 articles. But it is purified for various very important purposes. 

 When the most volatile portions are collected, what comes over are 

 the acid oils. Now, these acid oils consist of two acids, carbolic acid 

 and cressylic acid. Carbolic acid has the formula C^li^Oa ; and the 

 cressylic acid is what is called a honiologue of the other, or contains 

 CoIL more. It consists of Ci 4 H 3 O 2 . Common creosete is a mixture 

 of these two acids. This carbolic acid which forms common creosote 

 is, after purification, and when perfectly dry, a solid, and forms one 

 of the most powerful disinfecting agents. When this acid is treated 

 with nitric acid it loses part of its hydrogen, and that hydrogen be- 

 comes replaced by peroxide of nitrogen, a lower oxide of nitrogen 

 than nitric acid. When it is treated with nitrogen three of these go 

 away, and the hydrogen is replaced by what is termed a compound 

 radical a body which plays the part of hydrogen, and which forms a 

 yellow substance called carbazotic acid. Carbazotic acid is carboWc 

 acid, three of whose equivalents of hydrogen have been substituted 

 by three equivalents of an oxide of nitrogen. 



Now, this carbazofcic acid can be prepared in large quantity from 



