103 



are coiisiclercd by some to belong to the class of IsocoUoids (Wo. 

 Ostwalcl). f 



Drying Oils. 



The di-ying oils used in varnishes and in paints in contact with 

 water ought to behave like other vegetable oils in their power to yield 

 emulsions, and the generaUsations laid down in E. Hatschek's Report 

 (B.A. Reports on Colloid Chemistry, 2, 16), may be considered to 

 apply. {See also " Modern Conceptions of Emulsions," W. Clayton, 

 J.S.G.I., 38, 113, 1919.) 



The drying oils seem to differ among themselves m their emulsifying 

 power, although no drop number data are available. In the writer's 

 opinion soya bean and linseed oils are superior to China wood oil ; 

 moreover, polymerised linseed oils emulsify better than raw linseed 

 oil, but the emulsions aie less stable. The properties of the emulsions 

 with the soaps of the drjdng oils containing divalent metals are similar 

 to those of other vegetable oils. 



When a drying oil is thickened by heat out of contact with the 

 air a marked increase in viscosity and modification of other physical 

 and chemical properties are manifested. (The Chemistry of Linseed 

 Oil, J.N. Friend, 1917, contains a fuU bibhography of the subject.) 



Thickened linseed oil contains polymerised molecules, but 

 there is also evidence of the shifting of the unsaturated linkages 

 (Morrell, J. S.C.I. , 34, 105, 1915). Such thickened oils are considered 

 by Wo. Ostwald to belong to the IsocoUoid class which includes 

 petroleum, paraffin, liquid sulphur above 170° C.,and highly polymerised 

 Uquids. (Wo. Ostwald, " Handbook of Colloid Chemistry," 2nd Edit., 

 p. 102.) 



The IsocoUoids are considered to be composed of one chemical 

 substance ; in other words the disperse phase and the contu\uous 

 medium contain the same substance in different states. Their 

 internal friction shows remarkably high temperature coefiicients 

 varying greatly with changing temperature. Comparison with the 

 system stjTol-metastyrol is, perhaps, the best in considering thickened 

 drying oils (Lemoine, Compt. Rend., 125, 530, 1897, and 129, 719, 

 1899). Seaton and Sawyer {Jour. Ind. Eng. Chem., 8, 490, 1916), in 

 an investigation on the molecular weights of drjring oils and their 

 polymers have found that only in stearic acid as solvent were they 

 able to obtain values of the molecular weights which were mdependent 

 of the concentration of the solution or which showed absence of 

 combination of solvent and solute. 



In view of the complexity of composition of linseed oil with, its 

 varying amounts of mixed glycerides more reliable results may be 

 expected from China wood oil. 



C. J. Schumann {Jour. Ind. Eng. Chem., 8, 5, 1916) has investigated 

 the changes which Tung oil undergoes on heating. The oil at first 

 forms a simple polymeride and on further heating it sets to a stiff gel. 

 Schapringer {Chem. Zent. Blatt, 2, 1469, 1905), considers that the 

 gelatinisation proceeds in two stages, the first progressive, and the 

 latter instantaneous ; a case of mesomorphic polymerisation. (Kron- 

 stein, Ber. 35, 4150, 1902, and 49, 722, 1916.) 



