DYEING. 



247 



Processes 

 of Dyeing. 



Important 

 mi.-ukt 

 with respect 

 to the scar- 

 let Jyc de- 

 tected by Or 

 Bancroft. 



bright and less durable than that of the quercitron 

 bark. This last had also the advantage of being not 

 only the brightest, but the cheapest of all yellows ; since 

 one pound of the bark in powder, which cost but three- 

 pence farthing, dyed, with a sufficient quantity of mu- 

 riate of tin, between thirty and forty pounds weight of 

 woollen cloth, of a full bright golden yellow ; and this 

 being afterwards dyed in the same liquor, with one- 

 fourth less of cochineal than what is usually employed, 

 acquired a scarlet, equal in beauty and durability to 

 any which is usually given by the ordinary means with 

 a full proportion of cochineal ; and such were the ge- 

 neral results of a great number of experiments." 

 ' 257. Dr Bancroft was accordingly induced to make 

 trial of this method of dyeing scarlet on a large scale, 

 at the dye-house of Messrs Goodwin, Platt & Co. Bank- 

 side, Southwark ; but owing to the muriate of tin be- 

 ing either too much concentrated, or too highly oxy- 

 genized, the result was far from being attended with 

 the success expected. In a subsequent trial, in which 

 a nltro-muriate of tin was used, by mixing the muria- 

 tic acid with about one-third less than its weight of the 

 nitric, the mordant acted very feebly, or rather failed in 

 exalting the yellow colour of the bark, which took but 

 slowly on the stuff, and never rose higher than a straw 

 colour ; while a considerable quantity of yellow colour- 

 ing matter, united to the calx of tin, remained floating 

 in the bath, " not because the calx was too intimately 

 combined with the acid, as in the first experiment, but 

 because for want of a sufficient attraction between them, 

 it had been almost wholly decomposed as soon as they 

 were put into water; and in boiling, it fixed itself with 

 the bark colour upon the cloth very sparingly, superfi- 

 cially, and slowly. 



'2. r i*. " As this nitro-muriate of tin," says Dr Bancroft, 

 " though exempt from the defects of the muriatic so- 

 lution, had failed through others of a very opposite na- 

 ture, I was induced to mix much greater proportions of 

 nitric with muriatic acid, for dissolving tin. in order to 

 see how much of the former could be used in this way, 

 without so far yellowing the cochineal crimson as to 

 preclude the use of any of the quercitron yellow in the 

 dyeing of scarlet, an effect which I still expected from 

 the nitric acid, when used in a very large proportion ; 

 but, to my great surprise, I could discover no such ef- 

 fect, even when I had dissolved the metal in nitric acid 

 alone. . At first I suspected some impurity in tile aeid 

 which had been employed ; but having procured a fresh 

 supply, and ascertained its purity by the proper means, 

 I still found that tin dissolved by it, had not the least 

 tendency to change the cochineal crimson towards a 

 yellowish or scarlet hue; and that this effect, in the n,\nal 

 ii-iii/ af tit/fin* that colour, resulted wholly from the tar- 

 tar, (acidulated tartrite of potash,) which u always em- 

 ployed at lie same time. This fact I ascertained by repeat- 

 ed and varied experiments, in which I constantly found 

 that cochineal, with the dyer's common solution of tin, 

 and even with that made by nitric acid only, would pro- 

 duce nothing but a crimson, without tartar ; and that 

 cochineal, Kith tartar, would produce a scarlet, not on- 

 ly with these last mentioned solutions, but also, and 

 equally well, with the muriatic solution of that metal ; 

 and therefore that every thing which had l>een taught 

 and believed to the contrary, was repugnant to truth. 

 And here I cannot conceal my wonder, that an error of 

 o much consequence, and so destitute of all foundation, 

 should have been propagated and confirmed by so many 

 acute reasoners and sagacious observers in other re- 

 spects ; for, besides other eminent writers, Mr Poerner 



has more recently adopted and propagated the same er- Processes 

 ror, after making a great number of experiments, seve- ^*J "^j 

 ral of which, if they had been duly considered, would "~^~~ 

 have taught him the truth on this subject. This was 

 even more lately done by Berthollet, in his Elemens 

 tie I' A>t de hi Tf'mture, where, to adopt the words of 

 Dr Hamilton's translation, he says, " Tartar, as we 

 have seen, gives a deeper and more rosy hue to the co- 

 louring matter of cochineal, precipitated by the solution 

 of tin. It moderates the action of the nitro-muriatic 

 acid, which tends to give scarlet an orange cast, though 

 this orange cast is not to be seen in the precipitate pro- 

 duced by the solution of tin, which is, on the contrary, 

 of a fine red. It is probable that the solution of tin 

 gives scarlet an orange tinge, by means of the action 

 the nitro-muriatic acid exerts on the wool, which, as 

 well as all other animal substances, it has the property 

 of turning yellow. Thus, (adds he,) by putting more 

 of tartar into the reddening, a deeper and fuller scarlet 

 may be obtained ; and on the contrary, the scarlet may 

 be rendered more inclining to orange, by omitting this 

 ingredient." Here then it is manifest, (says Dr Ban- 

 croft.) that the nitro-muriates of tin are each supposed 

 to produce effects directly contrary to what are really 

 produced by thrm, the effects of each being ascribed to 

 the other ; a mistake capable of producing much dis- . 



appointment and detriment." In the last edition of his 

 Elements on Dyeing, Berthollet has accordingly, with 

 much candour, acknowledged his error, and admitted 

 the truth of Dr Bancroft's observations. 



259. Had Dr Bancroft's attempts to simplify and im- 

 prove the method of dyeing scarlet with cochineal, pro- 

 duced no other effect than the correction of a mistake, 

 which had prevailed so long and so universally, the re- 

 sult, even in this point of view, might have justly been 

 deemed important ; but the failures which he had hi- 

 therto experienced in realizing his speculative opinions, 

 instead of diminishing his confidence in his former rea- 

 soning, only increased his diligence in searching after 

 more suitable means for accomplishing his purpose, and 

 at length, after various experiments, he discovered that 

 the murio-sulphate of tin, the composition of which we 

 have already described (2 1 6.), formed an excellent mor- 

 dant for the process he had proposed. 



260. To dye a scarlet with this mordant, it is neces- New pr- 

 sary to put the cloth, suppose lOOlb. weight, into a cess, 

 proper tin vessel, nearly filled with water, in which 



about 8lb. of the murio-sulphuric solution of tin have 

 been previously mixed, to make the liquor boil, turn- 

 ing the cloth as usual through it by the winch, for a 

 quarter of an hour ; then taking the cloth out of the 

 liquor, to put into it about four pounds of cochineal, 

 and two pounds and a half of quercitron bark in pow- 

 der ; and having mixed them well, to return the cloth 

 again into the liquor, making it boO, and continuing the 

 operation as usual, until the colour be duly raised, and 

 the bath exhausted, which will be the case in about 

 fifteen or twenty minutes ; after which, the cloth may 

 be taken out and rinsed as usual. " In this way," says 

 Dr Bancroft, " the time, labour, and fuel necessary for 

 filling and heating the dyeing vessel a second time, will 

 be saved ; the operation finished much more speedily 

 than in the common way ; and there will be a saving 

 of all the tartar, as well as of two thirds of the cost of 

 xpii it, or nitro-muriatic solution of tin, which for dye- 

 ing 100 Ibs. of wool, commonly amounts to 10s.; where- 

 !l>s. of the murio-sulphuric solution will only cost 

 about Ss. There will be, moreover, a saving of at least 

 one-fourth of the cochineal usually employed (which > 



