and Dyeing Turley Red. 1 73 



dcs has been terminafed, and before the common ones are 

 put into the boiler, powdered jrall-nut or lluimac muft be 

 added, with a new but fmall portion of madder : the procefs 

 muft be managed alfo in fnch a manner, that the ebuhitioa 

 (hall not take place till two hours after, 



I feveral times tried to cxhanlt ihe madder bv fimple ebul- 

 lition, and without adding- anv thing elfe than chalk ; but 

 I found that this was unfavourable to all colours, black ex- 

 cepted : it even appeared that the ctfeft of the madder was 

 much lefs than when the heat was moderately applied, and 

 when the acctnnulated calorie cafily decompofed the colour- 

 ing fubftance. It is this tendency to be decompofed, and 

 particularly by fermentation, however little it be moiliened 

 or diluted with water, which has' hitherto prevented me from 

 obtaining a fubftantial colf>ur, pretty dark, and fufficiently 

 fixed to be applied on anv kind of tiuff. I t)l)ferved alfo, that 

 if the heat was carried too far tlie (irft time, in circumftances 

 when it was propofed to madder a fecond and third time, it 

 prevented me not only from obtaining bright and agreeable 

 fliades, but alio of the requifite intenfity. The aqueous ve- 

 hicle of the madder, at too high a temperature, never fails 

 to weaken the adhefive force of the alumine and the oxide of 

 iron to the ftufl', and to take fmm it a portion, which an ex- 

 perienced eye may cafily remark on cxamiuinir the bath. 



I fhall here repeat, that for conunon and low-priced articles 

 it is indif|.K'nfablv neceOarv to employ gall-nuts or (lumiac, 

 which will lave one half and even two thirds of the madder; 

 but the colours obtained arc ncith.er fo fixed nor fo bright. 

 'I'he addition of chalk, hoA-cvcr, nnilt not be omitted ; other- 

 wile the gallic acid will carry away a portion of tl;e alumine 

 and coloured oxide of iron, which will weaken the lliades, 

 and, by larnidiing the ftuffs, will alfo attack the white which 

 may have been prefeived in them. Without the addition of 

 Gull-nu's or Ihumac, it feemed to me impoflible to exhauft 

 the madder entirely of its colouring parts; which made me 

 prclume that their adficfion i,~ favoured by the vifcid nature 

 of the tanning principle of thefe aliringent fubliances, which 

 carry awav and combine with themfclvcs the colouring parts. 

 I (liall obfervc alio, tha« gall-nuts as well as (humac loie the 

 property of dyeing black ; and accjuire, on the »>ther liand, 

 that of dyeing or colotn-ing alumine yellow, oxide of iron 

 olive green, by the ad«lilif)n of chalk, the calcareous bale of 

 which unites itfelf to the gallic acid. Do thiTe yellow and 

 olie- green colours arifc from any peculiar fubllancc con- 

 tained in the grill-nuls and (humac, or are ibey indebted for 

 4 "^ ' their 



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