Manufacturer and builder 1, 1878
A new artificial dyestuff of a beautiful red color has costly been introduced in the trade, but the material from which it is made, as well as the manner of preparation is kept a secret. This having excited the curiosity of chemists, the Germans, as is usual in such order to find out what it is. Prof. Hoffmann found that it consisted of an organic acid combined with soda as a base, and this coloring salt is, in the same way as is the case with lakes, combined with a large quantity of alumina. It is very soluble in hot water - not much in alcohol, and forms a deep reddish-orange solution, which crystallizes in cooling. The crystals are insoluble in ether, and will stand considerable heat without chemical change. At a red heat they swell up and leave carbon behind, which soon burns up.
If the crude dyestuff is dissolved in boiling alcohol, strong chlorhydric acid added, and left to cool, fine needles crystallize out of the solution, to which however much incombustible materials (aluminum, soda, etc.) adhere, which, by repeated solutions in alcohol and crystallization, may be purified and the pure dye principle obtained,w hich consists of beautiful red-brown needles, also soluble in water, alcohol, and ammonia, but not in ether. From the ammoniacal solution it may be precipitated by an acid, which has then a deep violet hue.
The composition of this pure dye principle appears to be naphtho-sulpho acid, and diazo benzo; and, in fact, Hoffmann also obtained by the combination of these substances a new orange dye. In order to make the naphtho-sulpho acid, he digested naphthol with sulphuric acid in presence of oxid of lead. From the lead salt obtained the lead was precipitated by a current of sulphuretted hydrogen, and the remaining clear solution neutralized with carbonate of soda. To this solution he added nitrate of anilin and nitrate of potash, and obtained a red precipitate, which, after repeated solutions and re-crystallization in alcohol and hydrochloric acid, gave the same fine needle crystals that were obtained from the new dye; so that Prof. Hoffman was at last satisfied that he was on the right track, and had traced the ingredients and composition of the new secret dyestuff, while he gives the result of his investigations to the world for the benefit of all interested.