174 UOW OllOJ'S J'EKL). 



containing brine concentrates the latter where the two 

 are in contact, though the effect may be difficult to dem- 

 onstrate. 



Dcfecatiug Action of Charcoal on Solutions. — Char- 

 coal manifests a strong surface attraction for various 

 solid substances, and exhibits this power by overcoming 

 the adhesion they have to the particles of water when dis- 

 solved in that fluid. If ink, solution of indigo, red wine, 

 or bitter ale, be agitated some time with charcoal, the 

 color, and in the case of ale, the bitter principle, will be 

 taken up by the charcoal, leaving the liquid colorless and 

 comparatively tasteless. Water, which is impure from 

 putrefying organic matters, is sweetened, and brown sugars 

 are whitened by the use of charc^oal or bone-black. In 

 case of bone-black, the finely divided bone-earth (phos- 

 phate of lime) assists the action of the charcoal. 



Fixin,^ of Dye-Stutfs. — The familiar process of dyeing 

 depends upon the adhesion of coloring matteis to the fiber 

 of textile fabrics. Wool steeped in solution of indigo at- 

 taches the pigment permanently to its fibers. Silk in the 

 same way fastens the particles of rosaniline, which consti- 

 tutes the maizenta dye. Many coloi's, e. g. madder and 

 logwood, which will not adhere themselves directly to 

 cloth, nre made to dye by the use of mordants — substances 

 b'ke alumina, oxide of tin, etc. — which have adhesion both 

 to the fabric and the pigment. 



Absorptive Power of Tlay. — These ejects of charcoal 

 and of the fibers of cotton, etc., are in great part identical 

 with those previously noticed in case of sand and humus. 

 Their action is, however, more intense, and the efi'ects 

 are more decided. Charcoal, for example, that has ab- 

 sorbed a pigment or a bitter principle from a liquid, will 

 usually yield it up again to the same or a stronger solvent. 

 In some instances, however, as in dyeing with simple col- 

 ors, matters are fixed in a state of great permanence by 



