ROSENSTIEHL'S GREEN 721 



pound. The salt obtained by the action of concentrated hydrochloric acid is a com- 

 pound with three equivalents of acid. 



Exposed to 100 C., this salt gradually loses acid, the brown crystals becoming 

 indigo-blue ; and if the exposure be continued until the weight becomes constant, the 

 original green-salt with one equivalent of acid is reproduced. 



Sulphate of Rosaniline is readily obtained by dissolving the free base in boiling 

 diluto sulphuric acid. On cooling, the salt is deposited in green metal lustrous 

 crystals, which by one recrystallisation become perfectly pure. 



Acetate of Rosaniline. This is probably the finest salt of the series. Mr. Nicholson 

 obtained it in crystals an inch in diameter, which, on analysis, were found to be 

 the pure monacid acetate. The crystals of this salt, when freshly prepared, exhibit iu 

 a marked manner a beautifully green metallic lustre ; on protracted exposure to the 

 light this lustre disappears, and the crystals assume a dark reddish-brown tint. 



The acetate is one of the more soluble salts both in water and in alcohol ; on a 

 smaller scale it cannot be conveniently recrystallised. 



Nitrate of Rosaniline is easily formed by dissolving the base in warm dilute nitric 

 acid. On cooling, the salt crystallises in small crystals resembling the other salts of 

 rosaniline. 



Of the remaining salts of this base we may mention the chromate, which is obtained 

 by adding chromate of potash to a solution of the acetate, in the form of a brick- 

 red precipitate, becoming a green crystalline, almost insoluble, powder on ebullition 

 with water. 



The Tannates of Rosaniline, described by M. E. Kopp, are also very beautiful 

 salts ; they are true carmine lakes which rival the renowned carmine-lake obtained 

 from cochineal. They are entirely insoluble in water, but soluble in alcohol, wood- 

 spirit, and acetic acid. In the dry state they do not present the green metallic 

 appearance of the other salts of rosaniline, but preserve their beautiful carmine-red 

 colour. 



The tannate of rosaniliue is of considerable importance to industry, not only because 

 it is formed in nearly all the cotton fabrics dyed and printed in red or rose with ros- 

 aniline, but also because, by reason of its insolubility, it enables the manufacturer to 

 make use of very dilute aqueous solutions of aniline red, which are often obtained in 

 the factories during the purification of rosaniline. In fact, the best manner of' 

 treating these solutions, which are too poor in colouring-matter to be advantageously 

 employed in any other way, consists in precipitating them with a fresh solution of 

 nut-galls ; after a very short time all the rosaniline is precipitated in a state of mag- 

 nificent red lake, the mother-liquors becoming almost entirely colourless. 



Iodide of Rosaniline. Hobrecker, of Crefeld, discovered a violet colouring-matter, 

 derived from rosaniline, which crystallises easily, and is characterised by its rich 

 reddish tone. This colouring-matter is obtained by the action of a mixture of 

 chloride of benzyl and iodide of methyl upon rosaniline, dissolved in methylic alcohol. 

 The mixture is digested for some time in a water-bath. As the deep violet solution 

 cools, needles of a green metallic lustre separate out, and can be obtained completely 

 pure by re-solution in alcohol and re-crystallisation. The compound an iodide is 

 almost insoluble in water, sparingly soluble in cold alcohol, but more soluble in the 

 same liquid when hot. The iodide, dried at 100 C., was analysed by Hofmann, 

 with the following results: Carbon, 70'56 ; hydrogen, G'O ; nitrogen, 5 '89 ; iodine, 

 17-67: total, 100-12. 



ROSEINE. See ANILINE BED. 



ROSE&ET. The fur of the ermine Mustela erminea, as it is taken from the 

 animal in the summer. See ERMINE. 



ROSEMARY. The Rosmarinus officinale contains a volatile oil, and is used in 

 perfumery. 



ROSENSTIEHIi'S GXUBEXT, known also as Cassel green. This is a baryta 

 green, or a manganate of baryta. The best mode of preparing it is as follows, ac- 

 cording to M. E. Fleischer : On precipitating a green boiling solution of manganate 

 of potash with chloride of barium, there is formed a deposit strongly granular, but 

 not crystalline. This precipitate is of a violet colour, bordering on blue. It is well 

 washed by decantation, and then filtered. When dried, its colour becomes paler as 

 the temperature rises. At a dark red heat it is white, with a slight greyish-blue 

 tinge. If heated higher, with access of air, it becomes by degrees completely green, 

 then of a fine blue, and at very elevated temperatures it is converted into a dirty 

 brown-grey. If a solution of permanganate of potash is precipitated with chloride of 

 barium, and allowed to boil, there is slowly formed a reddish-violet deposit (colour of 

 peach-blossom), and the liquid retains an intense violet colour. The precipitate may 

 be washed by decantation, and filtered withoiit decomposition. It can evtn be dried 

 at 100 without losing its colour. When gradually heated, the permanganate of baryta 

 VOL. III. 3 A 



