105 



substance, although it contains unsaturated groupings. In oil varnishes 

 the function of linoxyn is of paramount importance. 



J. N. Friend (Chem. Soc. Trans, 111, 162, 1917) 'has. studied the 

 effects of heat and of oxidation on linseed oil with reference to changes 

 of density, viscosity, and coefficient of expansion. The problem is 

 complicated by the decomposition of peroxides with the loss of water 

 carbon (Uoxide, and organic vapours. There is an increase in volume 

 up to the setting point of the oil, after which contraction ensues, and 

 the expansion is dependent on the increase in weight. The contrac- 

 tion suffered by the linoxyn explains the cracking of old paint. The 

 action of driers is bound up with the formation of peroxides. (Ingle, 

 J.S.C.I., 36, 319, 1917, and Morrell, Chem. Soc. Trans., 113, 111, 

 191S.) 



From the writer's experience the peroxides undergo polymerisation 

 passing from viscid oils to varnish films. On exposure to air the 

 peroxides undergo slow decomposition. (Ingle, J. S.C.I. , 1913, 32, 

 and 38, 101, 1919, and Salway, Chem. Soc. Trans., 109, 138, 1916.)- 



The gelatmisation of drying oils and oxidation is a problem of 

 the greatest importance affecting the protective power of coatings 

 on wood and on metal. No doubt too much attention has been paid 

 to the interpretation by changes due to modifications in composition 

 or in orientation, but the distinctive and finer differences in the 

 qualities of the coatings often find no explanation on strictly chemical 

 grounds, and the investigator is driven to find some other cause. 

 Many observers have noted the importance of the presence of the 

 glyceryl radicle in the drying of an oil film although its presence has 

 no marked effect on rate or amount of oxygen absorbed. 



Primarily surface phenomena have to be studied and as yet 

 no adequate help has been, rendered by experience of other colloid 

 systems. The Avriter has experienced this difficulty for many years, 

 and is of the opinion that much can be learnt by closer investigation 

 on the lines of study of the properties of gels. (Morrell, J.S.C.I., 1920, 

 39, 153.) 



In the changes occurring during the drjdng of oils attention must 

 be paid to the surface action of the drier. Driers like lead and 

 manganese are iii coUoid solution, and according to Wenzel's Law 

 the amount of chemical change in unit time is proportional to the 

 absolute surface. If it be granted that there is a large absolute 

 surface in colloids many reactions will occur more rapidly and the 

 phenomena of catalysis are especially marked in colloid systems. 



Ostwald (" General Colloid Chemistry," p. 95) states that surface 

 tension may be either raised or lowered by chemical action occurring 

 in the two phases. A lowering of the surface tension between two 

 phases would accelerate the reaction. 



To the best of the writer's knowledge no such measurements in 

 reference to linseed oil have been pubfished. From his own experi- 

 ence from the measurement of the weights of drops in air by 

 Morgan's method (Amer. Chem. Journ., 33, 1911), no change in 

 surface tension of China wood oil before and after exposure 

 could be observed. Possibly the linox3Ti was insoluble because it 



