ANILIXE, OK COAL-TAR COLORS. 



25 



A further portion of it can be obtained from 

 the residue in tbe retort ; and the entire quan- 

 tity is finally to be distilled again and rectified. 



The aniline of commerce is never pure. As 

 benzole (CiH 6 ), in the ordinary modes of sepa- 

 ration, always holds and carries with it some 

 portion of at the least toluole (CuEU), so, 

 when nitro-benzole is prepared, there is formed 

 at tbe same time with it nitro-toluole ; and 

 finally, in the change in which, as commonly 

 stated, nitro-benzole is converted into an iline, 

 the nitro-toluole mixed with the former is in 

 the mean time and by a like reaction converted 

 into toluidine (C^HgN). The commercial ani- 

 line is always a mixture of at least these two 

 substances, and very probably contains minute 

 quantities of still other homolognes of aniline 

 proper. This very impurity of aniline, it will 

 presently be seen, is essential to the produc- 

 tion of the coloring matters. Dr. Phipson 

 gives the boiling-point of pure aniline as 35 9. 6, 

 and that of toluidine as 388.4 F. ; and he states 

 that the anilines sought for the manufacture 

 of the dyes are those having their boiling-points 

 between about 365? and 410 F., and which 

 are neceesarily, therefore, mixtures. 



As met with in commerce, aniline is a col- 

 orless, oily liquid, which sinks in water, and 

 has a vinous odor, and an acid, burning taste. 

 It is very slightly soluble in water, but readily 

 so in alcohol or ether. These qualities, also, in 

 much the same degree, belong to pure aniline ; 

 this, however, being lighter, and having a 

 lower boiling-point. Its specific gravity is 

 1.028. The formation of aniline from nitro- 

 benzole takes place by substitution of an equiva- 

 lent of amide in the former for that of hypo- 

 nitric acid; so that its formula is CioH 7 X. It 

 is a powerful organic base, having a resem- 

 blance to certain vegetable alkaloids, and com- 

 bining with many acids to form salts. A 

 characteristic quality of this base, that of 

 striking a fine purple blue with bleaching 

 powder and other oxidizing agents, and the 

 observation of which finally led to the de- 

 velopment of the aniline dyes, has been al- 

 ready mentioned. 



Some other derivatives of coal-tar besides ani- 

 line have been made to yield dyes ; as, certain 

 homologues of aniline, and also chinoline, naph- 

 thaline, carbolic acid, &c. The " coal-tar col- 

 ors " are thus much more numerous than the 

 "aniline colors," strictly so called; although 

 the latter expression appears sometimes to be 

 used as equivalent to the former. 



Since the time when Verguin and the Re- 

 nard brothers brought out the aniline crimson, 

 by action of a chloride of tin on aniline, other 

 chemists and manufacturers in different Euro- 

 pean countries have produced the crimson or 

 particular hues of it by the employment of a 

 variety of other oxidizing agents, among these 

 being chlorides of lime, carbon, mercury, iron, 

 and perhaps others of the metals, and also ni- 

 trate of mercury, nitric acid, bichromate of pot- 

 ash, ozone, arsenic acid. &c. The hues obtained 



usually vary with the nature of the oxidizer 

 employed ; and the consequence has been the 

 issuing of a proportionately large number of 

 patents, and also much litigation between dif- 

 ferent claimants. 



Perkin's aniline purple is a material quite 

 unlike in composition to the crimson or rosani- 

 line of Hofmann, with its derivatives. The 

 former appears, according to a late statement 

 of its discoverer, to consist essentially of mau- 

 veine (CsiH^X;), which plays with acids the 

 part of a powerful base. The aniline crimson 

 was at first never obtained pure, and accounts 

 of its composition varied Mr. Xicholson first 

 procured it in the pure state, by acting on the 

 boiling solution of the compound formed by 

 the crimson dye with acetic acid (a form in 

 which the material is quite generally used in 

 dyeing), by means of ammonia. The basic 

 substance is deposited from the liquid, on cool- 

 ing, in the form of needles and plates, which, 

 so far as entirely pure, are perfectly white or col- 

 orless. Dr. Phipson, however, cites M. Preisser 

 as having shown, some years ago, that most col- 

 oring matters in the pure state have no more 

 color than white sugar. For the name, roseine, 

 which Nicholson gave to this pure crimson dye, 

 i. e., magenta, but which is now appropriated to 

 another of these dyes, Hofmann, who analyzed 

 the former, substituted rosaniline. This body, 

 in the white crystalline, i. e., pure form, is in. 

 reality a hydrate of the true base; and in 

 Hofmann's latest expressions of it would be 

 represented by CioHiaN^ILO, equivalent to 

 C 4 oH 21 X 3 O. It forms with acids numerous 

 perfectly crystallizable salts, which possess the 

 vivid crimson color of the dye ; and as it enters 

 into these it contains no oxygen, and is repre- 

 sented by C 4 oHi9N 3 . The magenta dyes in 

 practical use are always some one or more of 

 such salts ; in the latter of which the color 

 seems to be developed. TVhen the pure white 

 crystals, however, of rosaniline are exposed to 

 the atmosphere, they rapidly turn pink, and 

 ultimately dark red, no perceptible alteration 

 of weight attending this change ; and when 

 dissolved in alcohol, they impart to the liq- 

 uid a deep-red color. Heated to 212 F. the 

 base loses a minute quantity of water ; and at 

 temperatures above 266 it is decomposed, 

 leaving a quantity of carbon and an oily liquid 

 containing much aniline. The rosaniline base 

 appears capable of forming three classes of 

 salts, containing respectively one, two, and 

 three equivalents of acid ; the monacid salts 

 are stable, and the dyes belong to this class. 

 The crystals of these salts, red when seen in 

 thin plates by transmitted light, are by re- 

 flected light of a rich greenish metallic lustre. 

 Being very hygroscopic, they require to be 

 kept from the air. 



After Prof. Hofmann had been for some time 

 engaged in the investigation of rosaniline, he 

 discovered that during the oxidation of aniline 

 there was formed another base, also a coloring 

 matter, and of a beautiful yellow color, which 



