109 



by benzene (Winkleblech, 7j. Angew. Chem., 19, 1953, 1906). Kerosene 

 benzol, carbon diaulphide, chloroform act similarly, but ether has no 

 effect, and produces no emulsions. Such emulsions are noticeable 

 in varnish analysis and are considered by Bancroft to be due to violent 

 shaking, causing drops of the second liquid, which have the power of 

 condensing colloid particles on the surface and coalescing to larger 

 complexes, to form a rigid emulsion with water. 



Colophony in the form of re'sinates behaves similarly to the soaps 

 of fatty acids in forming emulsions. Among the more recent contri- 

 butions to the subject may be mentioned the work of L. Paul {Kolloid 

 Zeits, 21, 176-91, 1917), who states that solutions of alkali and resin 

 soaps behave hke highly dispersed colloid systems. These colloidal 

 soaps combine with basic dyes to form coloured rosin lakes and are 

 characterised by the readiness Avith which they combine with 

 petroleum hydrocarbons (Z. angew. Chemie., 28, Ref. 415, 387, 1915; 

 and Seifen Zeitung., 42, 640, 659, 1915). The same author {Kolloid 

 Zeits., 21, 148 and 191) finds that certain fractions of the distillate 

 obtained by distilling a mixture of colophony with phenol or a and j8 

 naj)thol yield dyes with diazo and tetrazo- compounds. 



Just as in the case of fats, fatty acids, soaps, and tannic acid, the 

 surface tension of water is lowered by resins or resinates which may 

 be considered to assume emulsoid or suspensoid properties in different 

 dispersion media. J. Friedlander [Z. phys. Chem., 38, 430, 1901) 

 showed in the solution of rosin in 1 per^cent. alcohol how very slight 

 are the changes in viscosity of a liquid when it takes up a suspensoid 

 phase, and again a solution of rosin in alcohol containing a little water 

 possesses a relatively high temperature coefficient (5-6 per cent, per 

 degree temperature) against that of water, 2 per cent. (Hardy, 

 Z. phys. Chem., ZZ, 328, 1900). Cohn {Chem. Zeit, 40, 791, 1916) 

 describes gel formation produced when colophony is treated with 

 aqueous ammonia. 



A. P. Laurie and Clerk Ranken {Roy. Soc. Proc. A, 94, 53, 1917) 

 describe the imbibition exhibited by some shellac derivatives. The 

 solid which separates on cooUng a solution of shellac in boiling sodium 

 carbonate when immersed in water expands rapidly and ultimately 

 disintegrates to a flocculent precipitate. At the maximum point of 

 expansion the solid on immersion in a solution of sodium carbonate 

 contracts, expanding again when transferred to water. It was found 

 that the expansion was inversely proportional to the concentration of 

 the salt solution. Since the shellac molecule is here considered to 

 be permeable to salt solutions the mechanism of the expansion may 

 be accounted for by the passage of the salt solution through the 

 diaphragm, the soluble nucleus dissolving in the presence of the salt 

 solution and the amount which can dissolve controlling the consequent 

 osmotic pressure. 



Shellac films from spirit solutions do not absorb normal salts from 

 half normal solutions. The writer {loc. cit.) has found that the presence 

 of salts, e.g., N/2 KoSOj or N/2 KCNS reduces the water absorption 

 of the shellac film and no salt could be detected passing through it. 

 The water absorption by shellac is much less than in the case of 

 ordinary varnishes, but the effect is more permanent giving a cloudy 



