

DYEING. 





Or Ran- 

 i rwf"t" rca- 

 vming not 

 conclusive. 



Additional 

 experiments 

 of Or Ban- 

 croft, to dis- 

 prove Bcr- 

 thollct's 

 theory. 



place; anil this without any intermediate tint, which 

 would not have been the case, if the effect of the n\y- 

 muri.ttic acid hud, as M. Bcrthollet siip)x>ses, resembled 

 combustion. Anil, on the other hand, the Mack, on 

 which the oxymuriatic acid could make but a very slight 

 impression, was completely dotroved (excepting the 

 colour of its ferruginous lwisis) by the nitric acid." Dr 

 Bancroft accordingly infers, that the powerful action 

 exerted by the oxymuriatic acid on colouring matters, 

 does not result from the abstraction of its oxygen, 

 but from some quality peculiar to itself; " from the 

 combined agency of its constituent parts, and not 

 from the action of either separately, as has been sup- 



171. It is obvious, however, that, in reasoning con- 

 cerning the effects of the nitric and oxyumriatie acids, 

 the Dot-tor has confounded two things which are per- 

 fectly distinct: the acidity of these bodies, and their 

 disposition to part with their oxygen. Even admitting 

 that the quantity of oxygen contained in acid bodies 

 was proportional to their acidity, it would not follow, 

 that the most acid substances would most readily im- 

 part their oxygen to other bodies. The nitrous oxide 

 sup]x>rts combustion with a brilliancy little inferior to 

 oxygen gas itself; the nitric oxide, which, with the 

 same base, contains double the quantity of oxygen, so 

 far from supporting combustion, immediately extin- 

 guishes the greater number of burning bodies which 

 are plunged into it. It cannot be inferred, therefore, 

 that, because nitric acid possesses greater acidity than 

 oxymuriatic acid, the former must necessarily give out 

 more oxygen than the latter, to the substances brought 

 within the spheres of their activity. But though this 

 argument is by no means conclusive with respect to 

 the dissimilarity of effect produced by atmospheric air 

 and oxymuriatic acid, anil though several explanations 

 might be offered to account for the different results ob- 

 tained in the preceding experiments, in perfect consis- 

 tency with Berthollet's theory, the following facts, which 

 Dr Bancroft has stated, certainly tend to prove, that 

 whatever analogy may hold between the action of com- 

 mon air anil oxymuriatic acid, the latter cannot be re- 

 garded, in all cases, as a measure or indication of what 

 colours would suffer by exposure to sun and air. 



17~. He put into an empty glass-stopped phial, the 

 following colours upon separate bits of muslin, viz. 



" 1st. A fast madder-red, dyed topically by an emi- 

 nent calico printer, upon a basis, from acetate of alu- 

 mine applied by the block. 



" 2d, A fast yellow, dyed from weld upon the same 

 basis, by the same calico printer. 



" 3d, A fast yellow, dyed upon the same basis, from 

 quercitron bark. 



" 4th, A fine durable purple, produced by the co- 

 louring matter of the buccinum lapillus. 



" 5th, A logwood purple, produced by mixing with 

 a strong decoction of that wood as much muriate of tin 

 as rendered the former slightly acid, and, after thicken- 

 in ir the mixture with gum-arabic, applying it in spots 

 -lin ; which, after being properly dried, was wash- 

 ed with soap and water. 



" 6th, A full bright yellow, produced from a similar 

 decoction of the quercitron bark rendered slightly acid 

 by an admixture of nitro-muriatc of tin, made with two 

 parts of nitric to one part of muriatic acid ; gummed 

 and topically applied in the same manner as the log- 

 wood puqile, and in like manner dried, and after- 

 :ied. 



~'h, A similar yellow, made from the quercitron 



bark, only substituting murio-sulphatc of tin for the Dnr:' ,; 

 nitro-muriatc." ol' r..lmnA. 



17S. " I'pon these colours," snys Dr Bancroft, " I s "~- """" 

 poured oxymuriatic mid, with which Mr Aeciim had 

 recently supplied me, (and which I had kept secluded 

 from the light) until the phial was full ; utter which, in 

 less than two minutes, I found that the bit-, of muslin, 

 with the madder, weld, and quercitron colours, dyed 

 upon the aluminous II.-IMS, were become perfectly white, 

 by a complete extinction of their several colours. Whilst 

 the logwtxxl purple, that from the buccinum, and tile 

 quercitron yellows, with solutions of tin, were not ap- 

 parently changed. But, in about five minutes, the 

 logwood purple appeared to be losing body, as did the 

 quercitron yellows soon after; and a similar effect soon 

 became evident in the shell purple. In about fifteen 

 minutes from the time when these colours were immer- 

 sed in the oxymuriatic acid, the logwood purple had 

 nearly disappeared ; and this was the case of the quer- 

 citron yellows in about three minutes afterwards, and 

 of the shell pm-ple about two minutes later ; excepting 

 that a part of the latter, as well as a part of one of the 

 yellows given with tin, had each preserved a portion of 

 colour, by having been protected by the bits of muslin 

 from the sun's rays, which, as the sky was clear, had 

 had free access to the phial containing them at the 

 window where this experiment was made; a fact which 

 manifested the influence of solar light in promoting the 

 dc.-tructive action of the oxymuriatic acid on the co- 

 lours in question. It is here to be recollected," conti- 

 nues he, " that the three first-mentioned colours, dyed 

 upon the aluminous basis, would have resisted the ac- 

 tion of sun and air for two or three months, and the 

 madder for a much longer time ; and yet they were 

 completely destroyed in an eighth part of the tiir.e 

 which was required to destroy the logwood purple, and 

 the yellows with tin ; neither of which could have been 

 exposed to the sun and air for a single week without 

 becoming of a faded brown. It is also worthy of ob- 

 servation, that the Tyrian or shell purple was detroyetl 

 by the oxymuriatic acid almost as soon as the logwood 

 purple and quercitron yellows last mentioned, though it 

 would have resisted the sun and air probably fifty times 

 longer than either of them." These experiments cer- 

 tainly shew, that whatever similarity may subsist be- 

 tween the effects of oxymuriatic acid and atmospheric 

 air on colouring matters", the former cannot be regard- 

 ed as the very accurate test of the durability of colours, 

 which Berthollet was disposed to represent it. Indeed, 

 the only sure mode of determining the durability of 

 colours, appears to be direct exposure to air, sun, wa- 

 ter, and the other agents to which dyed stuffs are 

 most frequently exposed. We shall therefore subjoin Ouf 

 the observations of Hclloton this subject, together with mcthod o{ 

 his account of the methods employed by Dufay, which tlctenni- 

 laitl the foundation of the regulations adopted by the ning the 

 French government respecting fading and durable co- durability 

 lours: "The late Mr Dufay," says Hellot, " who had '" 

 been selected by government as a per-on whose labours 

 might greatly improve the art of dyeing, made experi- 

 ments on the subject, by dyeing wool of all colours, and 

 even with dyes of all sorts, used either for durable or 

 fading colours ; he even sent to the different provinces 

 for such as are not employed at Paris ; and, finally, he 

 collected most of the different substances which he con- 

 ceived might be employed in the art, and tried a very 

 great number of them," investigating their good or bail 

 qualities, without paying any regard to the prejudices 

 of the dyers. 



5 



