378 MUREXIDE 



form of crystals. The manufacture of the latter has been brought to such perfection 

 that, crystallised in the shape of magnificent needles, exquisitely beautiful and pure, it 

 has come into commerce at very reduced prices. 



Statistics of the Manufacture. We may form an idea of the extent of this manu- 

 facture, at a time when it had reached its culminating point, from a statement made 

 by Messrs. Schunck, Angus Smith, and Roscoe, that the weekly yield of murexide of 

 one factory only that of Mr. Kumney of Manchester amounted to no less than 

 twelve cwts., a quantity in the production of which, it is asserted, about twelve tons 

 of guano were consumed. The cost of murexide in paste was originally 30s. per lb., 

 but it has gradually fallen to half that price. 



Isopurpurate of Ammonium. According to a private communication from M. E. 

 Kopp, the isopurpurate of ammonium of M. Hlasiwetz, a product obtained by the 

 reaction of cyanide of potassium upon picric acid, is not only isomeric but identical 

 with the murexide obtained from uric acid. M. Kopp bases his opinion upon the 

 fact that in dyeing wool and silk with murexide the same processes are requisite, and 

 give the same results, whether the murexide employed be prepared from picric acid 

 or from uric acid. The dyed stuffs thus produced exhibit no greater differences of 

 hue than may be observed in fabrics dyed by means of aniline reds of different pre- 

 parations. The manufacture of murexide by means of picric acid and cyanide of 

 potassium is extremely simple. To a hot saturated solution of the cyanide is added 

 a solution of picric acid (one part dissolved in seven or eight parts of boiling water), 

 and the mixture allowed to boil for some time. On cooling it deposits a crystalline 

 mass consisting chiefly of impure purpurate of potassium. By filtering and squeezing 

 through linen, redissolving the crystalline mass in hot water, and adding carbonate 

 of potassium to the filtrate, the salt is reprecipitated : purpurate of potassium is thus 

 obtained, this salt being but slightly soluble in the alkaline liquid. This precipitate 

 is filtered off, pressed and redissolved in hot water ; sal-ammoniac is then added, 

 and on cooling, beautiful crystals of murexide are obtained. 



Murexide Dyeing and Printing. The first conception of the industrial application 

 of murexide appears to belong to Dr. Saac, formerly of Wesserling, Haut Rhin, now 

 of Barcelona ; the processes for dyeing wool and silk by murexide is due to M. 

 Depouilly ; the methods for printing with this material upon cotton were devised by 

 M. Ch. Lauth, who employs as mordants chiefly the salts of mercury, lead, and zinc. 



In order to dye silk purple, separate aqueous solutions of murexide and of corrosive 

 sublimate are prepared, containing respectively about five per cent, of colouring 

 matter and of salt. The solution of murexide is mixed in the cold with a certain 

 quantity of the sublimate, and the mixture is acidulated with nitric acid. In this 

 cold bath the silk is agitated until the desired shade of colour has been produced. 

 Subsequent immersion in a sublimate bath containing three per cent of the salt, 

 imparts to the colour its characteristic freshness and brilliancy ; qualities in which 

 it remained without a rival until eclipsed by the still more brilliant and more easily- 

 prepared aniline colours. 



In order to dye silk of a brilliant yellow, a salt of zinc is substituted for the salt of 

 mercury, the rest of the process remaining the same. When the fabrics of silk have 

 been dyed, they are passed through water rendered very slightly alkaline by means 

 of a little carbonate of sodium, after which they are washed. 



Wool may be dyed with murexide in different ways, either by using the corrosive- 

 sublimate bath first and then applying the murexide ; or, by first immersing the 

 fabric in the murexide bath, and afterwards fixing the colour, by passing the web 

 through water and a hot bath of corrosive sublimate to which a little acetate of 

 sodium has been added. Sometimes a certain quantity of nitrate of lead is added to 

 the murexide bath, in order to facilitate the fixing of the colouring-matter. 



In order to produce rose-coloured or purple tints by murexide upon cotton, nitrato 

 of lead and murexide are dissolved together in water. 



The printed cloth is first suspended in a damp room, then introduced into a room 

 pervaded by a slight ammoniacal atmosphere, which assists in fixing the purpur.ito 

 of lead ; and lastly, passed through a corrosive-sublimate bath, containing one and n 

 half per cent, of salt, to fix the colour firmly on the fabric. This process may be 

 conducted in various ways, but must always be based upon the employment of nitrate 

 of lead and corrosive sublimate. 



The murexide colours are very fresh and brilliant, and may be exposed to the light 

 without fading. They are, however, excessively sensitive to the action of sulphurous 

 acid, which tarnishes and discolours them with extreme rapidity. This drawback 

 becomes very serious in places where the use of gas has become general ; since in the 

 combustion of even well-purified coal-gas there is always enough sulphurous acid 

 generated to act upon fabrics dyed with murexide. 



Although the manufacture of murexide has dwindled to a mere shadow of what it 



