ANILINE-RED 183 



described above, there is always produced simultaneously a certain quantity of a green 

 colouring-matter, which may be purified by taking advantage of the circumstance that 

 it is freely soluble in alkaline solutions. When crystallised or precipitated by suitable 

 reagents, it is commonly known by the name of ' iodine-green,' and may be regarded 

 chemically as a double compound, resulting from the union of iodide of ethyl with the 

 already ethylated rosaniline. The colour has an affinity for silk and wool, it is re- 

 markably brilliant, and is much used on that account for dyeing bright green, the 

 shades being modified at pleasure by developing with picric acid. This body under- 

 goes a remarkable alteration by heat, which resolves it again into its constituents, the 

 colour changing from green to violet. 



The following method of applying the aniline-green dye on straw will be useful. 

 The straw is laid for some time in boiling water and then washed in cold water. It 

 is next bleached in a bath containing 20 grammes of chloride of lime, and 7 to 9 

 grammes of sulphuric acid. No more water is used than is needful to give sufficient 

 room for the straw to be well covered and turned about. It is then well washed in 

 cold water. A mordant is then made up of sumach, alum, and tartar. In this it is 

 well worked, and allowed to steep for 1 5 minutes. Half the mordant is then run off, 

 and the vessel is filled up with pure water. The straw having been taken out, aniline- 

 green, and, if necessary, picric acid, are added, and the straw is worked in this till the 

 right shade is obtained. 



ANIIiINE-RED. The discovery of this colour is clearly due to Dr. Hofmann. 

 In 1858 this chemist wrote, in the 'Proceedings of the Koyal Society' (vol. ix. 

 p. 284) as follows : ' The aqueous solution yields, on addition of potassa, an oily 

 precipitate containing a considerable portion of unchanged aniline ; on boiling this 

 precipitate with dilute potassa in a retort, the aniline distils over, whilst a viscid oil 

 remains behind, which generally solidifies with a crystalline structure. Washing 

 with cold alcohol, and two or three crystallisations from boiling alcohol, render 

 this body perfectly white and pure, a very soluble substance of a magnificent crimson 

 colour remaining in solution. The portion of the black mass, which is insoluble 

 .in water, dissolves almost entirely in dilute hydrochloric acid, from which it is re- 

 precipitated by the alkalies in the form of an amorphous pink or dingy precipitate 

 soluble in alcohol, with a rich crimson colour. The greater portion of this body 

 consists of the same colouring principle, which accompanies the white crystalline 

 substance.' 



This red colouration was indeed noticed in 1843 by Dr. Hofmann, while studying 

 the action of fuming nitric acid upon aniline. In 1856 Natanson observed it when 

 examining the action of Dutch liquid upon aniline. The industrial discovery of 

 aniline-red was made in 1859 by Messrs. Verguin and Kenard Brothers, of Lyons. 

 Their process for obtaining it was as follows : A mixture of ten parts of aniline, 

 and from six to seven parts of tetrachloride of tin, either anhydrous or hydrated, is 

 heated to ebullition for fifteen or twenty minutes. The liquid first becomes yellow, 

 and then gradually more and more red, until at last the colour is so intense that the 

 mass appears black. The mixture is allowed to cool, and then treated with a large 

 quantity of boiling water, which acquires a magnificent red colour, and, without any 

 other preparation, forms a splendid dye both for silk and wool. It is found advis- 

 able to previously purify the red colouring-matter, for which purpose its insolubility 

 in saline solutions is made available. If the concentrated red liquid be partially 

 saturated with carbonate of soda, and a quantity of common salt added, the 

 aniline-red is precipitated in a solid state, and constitutes thefuchsine of the chemist. 

 This has only to be dissolved in water, alcohol, or acetic acid to prepare the dye- 

 bath. 



Kenard and Franc stated, at the same time, that anhydrous mercuric, ferric, and 

 cupric chlorides might be used in the place of the chloride of tin. 



Several other processes for obtaining aniline-red were suggested, and some of 

 them used. Gerber-Keller treated aniline with the nitrates of mercury. Lauth 

 and Depouilly used nitric acid ; and six months before the discovery by these French 

 dyers, two English chemists Medlock and Nicholson had separately patented, 

 within a few days of each other, as the result of their experiments, a similar 

 process. 



Modlock and Nicholson, and Girard and De Laire, all, in 1860, patented the use of 

 arsenic acid. This process, being now almost exclusively employed, must be described. 

 Arsenic acid is combined with a slight excess of aniline; the crystalline mass is 

 heated by means of a slow fire to about 120 to 140 C., care being taken not to 

 exceed 160 C. The operation, according to the scale on which it is carried on, 

 requires from four to nine hours for completion. A perfectly homogeneous mass, fluid 

 above 100 C., is thus obtained, which on cooling solidifies to a hard substance, with 

 metallic bronze-coloured lustre. When dissolved in boiling water it produces a 



