I N D 



fome of the indigoes of the Ea(l Indies to thofe of America, 

 h perhaps owing to the former being prepared more cu- 

 rioufly from only the leaves of th^ plant ; and that by beat- 

 ing the herb in the fteeping-vat, which has been praftiTed by 

 fonie with a viewto increafe the quantity, great part oftlie fub- 

 ftance of the leaves and bark is blended with the water along 

 with the colouring matter, and the indigo extremely debafed. 

 It is faid that lime, or lime-water, is fometimes employed 

 in the beating- vat, to promote the fcparation of the tinging 

 particles from the water ; and that the hardnefs or flintinefs 

 of fome forts of indigo is owing to an over proportion of 

 this addition. 



Pomet fays, that the Indians of the village of Sarqueffe, 

 near Amadabat, ufe only the leave? of the indigo, and throw 

 away the plant and branches ; and from thence the moll 

 efteemed indigo is brought. 



Indigo is commonly divided, from the colour which it ex- 

 hibits upon breaking, into three kinds, copper-coloured, 

 purple, and blue. It is Hud that the dyers ufe chiefly the 

 firll ; and the calico-printers (for this drug gives a durable 

 ftain to linen as well as woollen) the laft. On what parti- 

 cular circumftances thefe different appearances depend, we 

 know not ; nor is it certainly known whether the real qua- 

 lity of the indigo has any conneftion with them. The deepeft 

 and hvelieft blue indigo, iibbed with the nail, appears like 

 polifhed copper ; and folutions of all the forts, made in alka- 

 line lixivia, affume alike a copper-coloured flfin upon the 

 furface. 



Good indigo is moderately light, breaks of a ihining fur- 

 face, and burns a'moft wholly away upon a red-hot iron. 

 It is quickly penetrated by water, and reduced into a kind 

 of pafte ; a conliderable part is at the fame time diifufed 

 through the liquor, and very flowly fubfides. This is pro- 

 bably what Labat and Heilot mean by its diffolving in 

 water ; for no part of the indigo really dilTolves ; it cannot 

 indeed be expedled that it fhould, from the procefs by which 

 it is obtained. 



Indigo requires an equal quantity or more of fixed alka- 

 line fait, to render it totally foluble in water. On digefting 

 the indigo, with a gentle heat, in the folution of the alkaline 

 fait, a fhining copper-coloured fkin begins to appear, and 

 gradually covers the whole furface : on agitating the matter, 

 a large blue flower or froth arifes, and the liquor underneath 

 appears of a deep green. If woollen cloth, without any 

 other preparation than moiftening it with warm water, be 

 dipped in this hot liquor, it comes out perfettly green, and 

 changes almoft inftantly in the air to a fine blue. This is 

 the common procefs of dyeinir blue. 



Mr. Heilot defcribes two indigo vats with urine ; one of 

 which is ufed hot, like the foregoing, and the other cold. 

 The hot vat confiils of equal parts of indigo, alum, and 

 tartar, digeiled in urine till the liquor becomes green. The 

 cold one is prepared, by digeiling powdered indigo with 

 vinegar for twenty-four hours, in the proportion of four 

 pounds to about three quarts ; then mixing the matter with 

 about fifty gallons of urine, and llirring the whole together 

 every night and morning, till the liquor turns green, and 

 gathers a head like the common vat. 



Indigo is fitted for printing on linen, by diluting it with 

 ■water into the confiftencc of a fyrup ; then adding fome 

 powdered pearl-afhes, green vitriol, and lime newly flaked ; 

 with fo much water, orcafionally, as will reduce them into 

 the confiflence of thin paint ; mixing the whole thoroughly 

 together, and ftirring the matter every now and then, till it 



fains a copper colour on the furface. The proportions ufed 

 y the workmen are, two parts of indigo, one of pearl- 

 afhes, three of vitriol, and two of lime. The fame compo- 



I N D 



fition, diluted vnth ?. fufRcient quantity of water (about fix 

 gallons to a pound of indigo), and boiled, gives a durable 

 blue to tanned fl<ins, whether dipped in hot or cold. 



Indigo digefted in a moderate heat with different volatile 

 alkaline fpirits, gave only yellowifli and brownifh red tinc- 

 tures ; with rectified fpirit of wine, a rcddidi one ; to lime- 

 water, and to water acidulated with the vitriohc, nitrous, 

 and marine acids, it gave no tinfture at all. 



The concentrated vitriolic acid unites with it into a fmooth 

 pafte, efpecially if the indigo is previoufly well ground with 

 powdered glafs, fand, or other like fubftances. The indigo 

 is thus rendered foluble in boiling water along with the acid, 

 fo as to pafs through the pores of a filter ; the folution, 

 whilll liot, appears of a deep bright green colour, like that 

 made by fixed alkalies, but fades as it grows cold, and 

 changes at lall to a brownifh. Thefe experiments, which 

 were many times repeated with the fame event, feem to over- 

 turn Mr. Hellot's ingenious theory, which deduces the 

 green colour of folutions of indigo from the common pro- 

 perty of blue juices being turned green by alkalies ; and the 

 blue colour which the cloth acquires foon after it is taken 

 out of the vat, from a feparation of the alkali. We here 

 find, that a green folution of this concrete is obtainable by 

 the ftrongefl of the acids, and that with volatile alkalies it 

 difcovers no tendency to greennefs. 



For the method of preparing Saxon Hue and Saxon 

 green from indigo, fee thofe articles. 



Indigo is fometimes ufed among the painters for paper- 

 hangings, and fuch grofs ufes, who grind and mix it with 

 white to make a blue colour ; for without that mixture it 

 would paint blackifli. 



They alfo mix it with yellow to make a green colour. It 

 is alfo ufed in dyeing, and by the laundrefTes, to give a blueidi 

 call to their linen. 



In the Hortus Indus Mahbaricus is an account of the 

 plant whence indigo is drawn ; the decoftion of Vvhofe root 

 is faid to be excellent againft nephritic colics ; its leaves, ap- 

 plied to the abdomen, good to promote urine ; and the in- 

 digo itfelf is faid to be of good ufe in drying of tumours. 



Some phyficians have recommended indigo in the quantity 

 of a drachm, while others look upon it as a poifon ; and in 

 Saxony the internal ufe of it is prohibited. 

 Indigo, Bqjlanl. See Amorpiia. 



Indigo Mills. For the purpofe of effecting the folution 

 and union of indigo with the liquid ufed along witli it, for 

 the purpofes of dyeing, mills of various conflruftions are in 

 ufe. In this procefs trituration or friction is as much as 

 poffible avoided, and the pulverization is effefted merely by 

 bruifing. For this two very fufficient reafons may be af- 

 figned ; the firft, in point of economy, and the fecond, to 

 avoid chemical inconveniency. On whatever fubllance the 

 indigo was triturated or rubbed, a certain proportion of the 

 fluff would be mixed or incorporated along with the pulve- 

 rized indigo, and that proportion of indigo which was ab- 

 forbed by this ftuff would be either totally loll, or brought 

 into union with another fubllance which might prove ufelefs, 

 and probably injurious in the fubfequcnt procefs of dyeing. 

 If the former only was the cafe, the abforbed indigo would 

 be totally loll ; if the fecond took place, the whole procefs 

 might be utterly fpoiled by the combination. In the appropri- 

 ate plate, _/f^. I. reprefents the ground or horizontal plan of 

 fuch an indigo mill as is generally ufed in fmall dye-works, 

 and which is occafionally turned by a man's or boy's hand. 

 This is tedious and laborious, for the operation mull be 

 continued for a very long time before the indigo is fuf- 

 ficicntly mixed with the liquid to be fit for ufe, and only a 



fmaU 



