312

DYEING AND CALICO PRINTING .

chemical agents—what beautifies the one injuring the other; so that if boththese colours occur on the same piece the beauty and brilliancy of one ofthem will be of necessity sacrificed to the other.

Even as late as the middle of the first quarter of this century field bleachingand boiling the goods in bran-water were the chief modes of clearing in use.The application of soap for clearing purposes dates from the year 1804, whenit was first used by M. D. Koechlin, who also appears to have occasionallyemployed chlorine.

The modern processes for clearing madder-dyed goods have been graduallydeveloped, and are more the result of accidental discoveries than of a regularlystudied course of research. For clearing of rose-reds and reds by themselvesalmost every printer and dyer has his own peculiar method, but generallythe following is an outline of the process applied:—Soap baths, a tin-saltbath, and a boiling up of the goods under pressure with crystallised carbonateof soda and soap. The ingredients used and their proportions may be learntfrom the undermentioned examples:—1. Soap bath—Water, 1200 litres;white soap, 4 kilos, for goo metres (g84’267 yards) of cloth ; temperature, 56°;time of immersion, one hour and a quarter. 2. Washing in machine withcold water. 3. Bath of nitro-muriate of tin (perchloride of tin)—Water,800 litres; solution of the tin preparation, 1*5 litres for 300 metres of cloth;temperature from 56° to 62°; time of immersion, from fifteen to twentyminutes. 4. Washing in machine as in No. 2. 5. Second soap bath—Water,

1200 litres; soap, 3 kilos.; cloth, goo metres; temperature, g4°; time, threequarters of an hour. 6. Again washing in cold water. 7. Third soap bath—Water, 1200 litres; soap, 3 kilos.; cloth, goo metres; temperature, g4°;time, three quarters of an hour. 8. Another washing in cold water, g.Boiling in a closed boiler under pressure—Water, 1200 litres; soda crystals,2-5 kilos.; soap, 2*5 kilos.; time, two hours. 10. Again washing in coldwater. 11. Warm bath at 50° during thirty minutes’ time.

Field bleaching in combination with some of the above operations is stillin use for certain styles, chintzes, and furniture prints, because the tints be-come more transparent. As regards the adtion of these different operations,at the first soaping the goods lose much colouring matter; the liquid, indeed,becomes rather deeply red. This is partly due to-the colouring matter, whichhad been temporarily fixed to the white portions of the tissue, and partly alsoto such of the constituents of the madder as yield less fixed permanentcolours than alizarin, viz., purpurin, and, more so, pseudopurpurin combinedwith the mordant while in the beck.

Dr. Schiitzenberger has demonstrated that properly mordanted cloth dyedby means of pseudopurpurin yields to a soap bath the greatest portion of itscolour. Soap, moreover, has the effedt of dissolving the greater part of theyellow matters, which cause the dulness of the colours. The adtion of thesoap is not simply detergent, for in consequence of a more or less completedecomposition of the soap,* a portion of the fatty acid is precipitated on thetissue, and combines either chemically or mechanically by a strong adhesionwith the coloured lake, thereby communicating to that substance a far greaterfastness and power of resisting the adtion of light and solvents than it

* The reader is reminded that soap is in a chemical sense a salt made up of a base anda fatty acid.