LO-KAO.
429
China a few years previously, that it had been dyed green by a substance un-known in Europe.* * A piece of this cloth having been sent to M. Persoz forinvestigation, he found that the dye was of organic origin, and quite differentfrom any then known in Europe. The first genuine sample of the dye-wareever sent to Europe was received by M. Persoz,f through the kindness of M.Forbes, then United States Consul at Canton. Shortly after this sample hadbeen sent to Paris a comparatively large quantity of lo-kao came via Bataviato Holland, and having attradled the attention of the silk dyers at Lyons, wassold at 533 francs per kilo.
Lo-kao is met with in commerce, or rather was, since it is now-a-daysalmost entirely superseded by the aniline greens, in the shape of thinlaminae, varying in thickness of from 1 to 4 millimetres, and from 2 to 5 centi-metres square. These laminae exhibit a blue colour, with a violaceous or greenreflection; they are fragile, yet difficult to pulverise, becoming a pasty mass.Lo-kao contains from 2i'5 to 33 per cent of ash, chiefly oxide of iron, lime,and alumina; 9-3 per cent of water; and 6 i-g per cent of colouring matter.It is decomposed by heat, but does not yield any sublimate; it is insolublein alcohol, wood-spirit, sulphide of carbon, and ether. Water does notdissolve lo-kao, but makes it swell up; dilute and cold acetic, hydrochloric,sulphuric, and tartaric acids aid its solution. With the aid of heat thesolutions of lo-kao are rendered olive-brown by concentrated acids, an iron-grey precipitate being deposited, and the supernatant liquid becomes yellow, andturns orange on the addition of an alkali. Concentrated sulphuric aciddissolves lo-kao, yielding a reddish brown solution.
Alkalies at first aid the dissolution of this green pigment, but when it isleft a long time in contadt with the alkaline fluid the colour turns brown, andmore rapidly at a boiling temperature, being converted into a new pigment,which cannot be again made green, but which has the property of becomingfixed upon previously mordanted cotton. The alkaline carbonates also destroythe green colour on prolonged adtion along with water at a pressure of from2 to 3 atmospheres.
The reducing acids, such as phosphorous, arsenious, hyposulphurous, oxalic,and formic, when added to lo-kao, cause the formation of a purple-violetprecipitate. Hydrosulphuric acid converts lo-kao and its solutions into ablood-red substance, but by the adtion of air the liquid becomes graduallygreen again, after having passed through a series of intermediate shades.Hydrosulphuret of ammonia also reduces and energetically dissolves lo-kao.Protochloride of tin dissolves lo-kao largely, and turns its colour blood-red.
liv., 415; ]v., 290. "Repertoire dc Chimie Appliquee,” 1 ., n, 75, 78, 370; ii., 53; iv., 405.Buchner’s “ Repertorium,” viii., 6g. "Bulletin de la Societd Industrielle de Mulhouse,”xxv., g6. “Notice du Vert de Chine et de la Teinture en Vert chez les Chinois," par M.Natalis Rondot; suivie d’une " Etude des Propridtes Chimiques et Tindtoriales du Lo-kao,”par M.J. Persoz; et de “ Recherches sur la Matidre Colorante des Nerpruns Indigenes," parM. A. F. Michel. Paris: chez Lahure et Co., 1858.
* Letter from the Chamber of Commerce of Mulhouse to the then Minister of Commerce,&c., viz., M. Dumas, 27th April, 1850.
t This is the statement as found in the published papers above quoted, but from a privatecommunication we know with perfedt certainty that a sample of the dye was brought over alongwith the cloth.