234 ANNUAL OF SCIENTIFIC DISCOVERT. 



was produced. He named it purpurate of ammonia. This substance, when 

 dry, has the appearance of a dark-red powder, soluble in water, to which it 

 communicates a magnificent red color. This solution not only gives a pre- 

 cipitate with metallic salts, but, when evaporated, yields beautiful crystals, 

 having the irridescent appearance of the wings of cantharides. 



This discovery has also been useful to medical men, by enabling them to 

 distinguish the uric acid calculi. 



Messrs. Liebig and Wohler had also investigated the subject, and succeeded 

 in obtaining from the uric acid contained in the faces of serpents this sub- 

 stance, which they called murexide, and a new class of organic substances, 

 the knowledge of which has much facilitated the application of murexide to 

 dyeing and printing. Mr. Saac was the first to apply the products of uric 

 acid to the dyeing of fabrics; his process consisted in dipping woollen fab- 

 rics, prepared with a salt of tin, into a weak solution of alloxan, a pro- 

 duct discovered by Liebig and Wohler, in heating urea with nitric acid. The 

 fabic so prepared was then dried, and when submitted to heat, a fine crimson 

 was generated, the intensity of which was increased by the fumes of ammo- 

 nia. But, owing to the difficulty of obtaining a color of uniform shade, 

 Mr. Saac's process required improvements, and these have been effected by 

 Mr. Schlumbcrger. 



The process followed by Messrs. Saac and Schlumberger, could not be 

 applied to silk or cotton fabrics. The method of dyeing silk with murexide 

 was discovered by M. de Pouilly, who adopted the following processes, viz., 

 dipping the silk in a concentrated solution of bichloride of mercury mixed 

 with murexide, squeezing the silk well, and han.iring in the air, when a mag- 

 nificent crimson insoluble compound is fixed on the silk. This effect is pro- 

 duced from the fact, that, when solutions of bichloride of mercury and 

 murexide are mixed together, an insoluble compound is only formed after 

 the lapse of an hour or two. 



The process for dyeing cotton is due to Messrs. Lauth and Schlumbergcr, 

 and consists in producing on cotton a purpurate of lead by mordanting with 

 nitrate of lead, passing into an alkali, and then dyeing in a solution of 

 murexide; in order to give full brilliancy to the color, it is lastly passed 

 through a weak solution of bichloride of mercury. This process was fur- 

 ther improved by Messrs. Dolfus, Meig & Co., in France, and Mr. Lightfoot, 

 in Lancashire, by printing murexide with an excess of nitrate of lead, and 

 subjecting the cloth so printed to the action of ammoniacal fumes, or passing 

 through a solution of caustic soda mixed with sal ammoniac. In order to 

 render this substance more generally useful, it remained to find a method 

 for obtaining fast colors with it on mixed fabrics, such as mousseline de 

 laine, and this has also been effected by Mr. Schlumberger. The cloth is 

 first prepared by uniting binoxide of tin with the wool. This object is 

 attained by using a salt, known to calico-printers as pink salt, the double 

 chloride of ammonium and tin, and then printing on the prepared fabric 

 the following mixture : 



1 part of murexide. 



6 parts of nitrate of lead. 



2 parts of nitrate of soda. 



The pieces are then allowed to age for two or three days, when, to fix the 

 pnrpurate of lead on the cotton, and the purpurate of ammonia on the wool, 



