PINCOFFEST 



577 



Picric acid is used for dyeing silk and wool of a yellow colour. Its colouring power 

 is very considerable, and it exhibits a great affinity for nitrogenised substances. The 

 colour resists the action of light very well, but it is somewhat affected by washing, 

 particularly with soap. It is rendered more stable by mordanting the material with 

 alum. 



Cotton, hemp, and flax, do not show any affinity for picric acid. The acid may 

 therefore be employed to distinguish silk and wool from cotton and flax. For this 

 purpose it is only necessary to plunge the tissue in a boiling solution of picric acid, 

 and then wash in water. The silk and wool will assume an intense yellow colour, 

 whilst the cotton and flax remain perfectly colourless. 



The use of picric acid for dyeing purposes was first suggested by M. Guinon of 

 Lyons, in 1845. 



Picric acid, under the influence of reducing agents, produces other colouring- 

 matters ; treated with ferrous salt and an alkali, for example, it produces a red acid 

 (Wohler's nitro-haematic acid). Under the influence of cyanide of potassium, again, 

 it gives rise to a purple potassium salt (Mr. Hlasiwetz's isopurpurate of potassium). 

 This purpurate, treated with an ammoniacal salt, produces an ammonaical compound, 

 which, when applied to dyeing, acts like the murexide of uric acid, giving, in fact, 

 precisely the same tints. Under the influence of chloride of tin, picric acid may even 

 produce, blue, purple, and red colouring-matters ; but the nature of these substances 

 is very little known, and not one of them has as yet (1862) received any practical appli- 

 cation. Hofmann. 



Instead of free picric acid, the alkaline picrates have been used in dyeing. This 

 practice is to be condemned since these salts are highly explosive, and are indeed used 

 on the Continent as explosive agents. Picrate gunpowder is prepared, in which 

 picrate of potash replaces saltpetre. Picrate of ammonia enters into the composition 

 of many coloured fires. The isopurpurate of potash mentioned above is now used as 

 a dye under the French name of Grenat soluble. 



PXCROMEXi is the name given by M. Thenard to a black bitter principle which 

 he supposed to be peculiar to the bile. MM. Gmeliri and Tiedemann have since called 

 its identity in question. 



PXCXtOTOXXlff (Picrotoxic acid) is an intensely bitter poisonous vegetable 

 principle, extracted from the seeds of the Menispermum cocculus (Cocculus Indicus), 

 It crystallises in small white needles, dissolving in boiling water and in alcohol. It 

 does not combine with acids, but forms combinations with alkalis. 



P2ETRA DURA. Ornamental work, executed in coloured stones, representing 

 flowers, fruits, birds, and the like. The Florentine work and the inlaid marble v/ork 

 of Derbyshire are of this character. 



PIG* IRON. See IRON. 



PIGMENTS. See COLOUKS ; PAINTS. 



PIMENTO. (Myrtus pimenta, Linn. ;Eugeniapimenta, DeCandolle.) Allspice, or 

 Jamaica pepper. This plant is cultivated in Jamaica in regular Pimento walks. The 

 full sized-fruit is gathered green and sun dried, during which process it is frequently 

 immersed. It is sent to the English market in bags of 1 cwt. each. This fruit con- 

 sists, according to Bonastre's complicated analysis, of : 



or Betel Nut. See AHECA. 

 PINCHBECK. A yellow metal, composed of 3 ozs. of zinc to 1 Ib. of copper. 

 See ALLOTS ; BRASS. 



PIMrcoFFW, or Alizarine commercials Under these names, some years ago, 

 VOL. III. P P 



