320 SCIENCE PROGRESS 



they obtained by precipitating a solution of cellulose in 

 ammoniacal copper-hydrate by means of an acid. So obtained 

 it contains hydro-cellulose which has a greater affinity, or 

 absorbing power, for basic dyes than cotton has, so to render 

 them more alike in behaviour both were mercerised. The work 

 was carried out at a uniform temperature of 14 — 17° C. and it 

 was found that 



C f 



^C w 



= K, 



thus showing that the general partition law holds for other 

 fibres than silk. 



The actual value, however, for 



Q K 



^C w 



is less for mercerised cotton than for mercerised precipitated cellu- 

 lose, i.e. the latter appears to take up more dye. This, however, 

 is dependent on the temperature, for at ioo° C. the reverse is 

 the case. The increased attraction of the powdered cellulose is 

 probably due to its greater surface area, but owing to the same 

 cause the powder offers less resistance to the increased solvent 

 action of the water at high temperatures and thus loses colour 

 more readily than the fibre. This again points to " surface 

 effects" or ''adsorption phenomena" as being the true cause 

 of dyeing. 



Schmidt in 1894 from experiments on the absorption of picric 

 acid by cellulose and of malachite green and eosine by silk could 

 obtain no constant ratio of the form given above, so Walker and 

 Appleyardm. 1896 re-investigated this point. They studied the 

 absorption of picric acid by silk, estimating the acid volumetric- 



N 

 ally with — K O H with lacmoid as an indicator. If the solid 



J 20 



solution theory applies, it is a matter of indifference whether 

 the picric acid is originally all in the silk, all in the water, 

 or distributed between these two substances in any ratio 

 whatever. The final equilibrium must always be the same, 

 being determined only by a certain ratio of the concentrations 

 in the water and in the silk. If the original concentration in the 

 silk is too great, it will lose picric acid to the water. This was 

 confirmed by Walker, but he pointed out that such a result is 



