320

DYEING AND CALICO PRINTING.

clearing there are printed on this cloth stripes of buff (an iron mordant), ablack will appear on those stripes which are touched by the buff, while thatcolour is not altered on the white portions. This proves that during thedyeing process the tannin has only become fixed on those portions of thecloth which are mordanted with alumina. A similar effedt may be obtainedby substituting for nut-galls any other astringent, as, for instance, quercitronor sumach. 7. Cloth uniformly dyed with Turkey-red is in some parts coveredwith a thin paste containing tartaric acid and an iron salt. After dryingthe cloth so prepared is immersed in a bath containing a solution of bleaching-powder. This substance does not a< 5 t upon the Turkey-red dyed portion atall, but the portions where the acid is printed are discharged, while at thesame time on these spots the iron is deposited, hydrated oxide being pre-cipitated on the fibre. If the cloth is next, after previous washing, placed ina somewhat acidulated solution of ferrocyanide of potassium, prussian blueis produced upon the portions of the cloth where the red was discharged.8. M. Carlos Kcechlin has published* the following interesting effedt of con-version operated upon a madder-dyed cloth:—

M. Persoz first observed that madder purple when treated with hydrochloricacid is turned to an orange-yellow: if cloth so treated is next placed in a milk oflime bath it becomes a beautiful bluish-purple, exhibiting great brilliancy. Whengarancin-dyed purples are similarly treated there is only an amaranth colourproduced. This difference as regards the garancin is simply due to theabsence of lime from the purple-lake which garancin yields on cloth ; for ifthere is added to the beck containing the garancin an excess of lime, so as toproduce a colour which resists strong soaping, the treatment with acid, andsubsequently with milk of lime, will have the same effedt as on madder.

When a pattern dyed purple with madder or fieur de garance is immersedin sulphuric acid, sp. gr. 1*116, and next washed in water, and afterwardsimmersed in a solution of aluminate of soda without excess of alkali (thealuminate made from Bauxite), the pattern will become instantaneously red,and the quantity of alumina which becomes fixed is in the diredt proportion tothe strength of the iron mordant originally printed on the cloth, and havingserved to produce the purple pattern. It therefore appears that the acid(sulphuric just named) discharges the iron of the mordant, leaving the colouruntouched, and the latter—as soon as brought in contadl with the aluminateof soda—attradls alumina therefrom, combining with it instead of with theiron which had been taken from it. The reds so obtained may be soaped, butdo not resist this operation so well as do the reds obtained by ordinarymethods.

As regards the opinion of M. C. Koecnlin upon the adlion of the lime forfixing the purples, M. Mathieu-Plessy observes that the alcoholic extracts offieur de garance and garancin, neither of which contain any lime, yield indyeing—distilled water being used—very fast purples, which, if treated asabove described with hydrochloric acid, behave exa< 5 tly as madder-dyed purples.This fa< 5 l proves that, as regards the cause of the want of fastness of garancin-dyed purples, there is some unknown circumstance, and that it is not solelydue to the absence of lime.

* “Note sur la Teinture par Substitution” (Bulletin de la Societe Industrielle de Mul-house, vol. xxviii., p. 119).