MICROSCOPICAL TECHNIC 425 



in response to a fundamental law but that various complicating 

 factors enter, great variations being possible by reason of the variety 

 of dyes and fabrics. 



OTTO N. WITT proposed the theory that the dye occurred in the 

 fiber in solid solution. This assumption can only apply to the initial 

 stages as G. v. GEORGIEVICS showed, in experiments on the absorption 

 of acids by wool. The further absorption of dyes, in general, corre- 

 sponds to an adsorption. This is the result of quantitative studies 

 of the distribution of dyes between fiber and liquor (the technical 

 name for the dye solution). 



We owe this knowledge to the researches of J. R. APPLEYARD and 

 J. WALKER, W. BILTZ, H. FREUNDLICH and G. LOSEV, G. v. GEOR- 

 GIEVICS and L. PELET-JOLIVET; these experiments show, moreover, 

 that there is no essential difference between the adsorption of formic 

 acid by blood charcoal and of indigo-carmine by silk. What ap- 

 plies to textile fibers we may apply as well to animal and plant 

 tissues. 



In technical dyeing which has formed the chief basis of theoreti- 

 cal studies, the addition of electrolytes (NaCl, Na^SO^ etc.) are im- 

 portant factors which modify the state of swelling of the fabric and 

 markedly influence the tendency of the more or less colloidal dye to 

 precipitate; in biological staining electrolytes are not used to such 

 an extent, but they always enter as factors. 



The course of the adsorption curve requires that proportionately 

 much more dye shall be removed from a very dilute solution than 

 from one that is more concentrated, an observation which impresses 

 every one who investigates dyes. 



It must be assumed if adsorption phenomena are involved, that 

 the entire dye may be removed by sufficiently prolonged washing, 

 i.e., that the process is reversible; this, as is well known, is contrary 

 to the facts. The adherents of the adsorption theory maintain that 

 traces of the strongly adsorbed dyes which can no longer be recog- 

 nized in the dye bath or wash water are in adsorption balance with 

 the dye taken up by the fiber. 



In most cases of true dyeing, fixation may be brought about by 

 secondary intercurrent chemical processes between fiber and dye. 

 This firm union between fiber and dye is what the adherents of the 

 chemical theory of dyeing (M. HEIDENHAIN, E. KNECHT, W. SUIDA 

 and his pupils) chiefly advance in support of their theory. They say, 

 in general, that the textile fiber is a complex organic substance which 

 undergoes a double decomposition with a dye salt, just the same as 

 any other salt; the result of this double decomposition is on the one 



