107 

 The application of Hatschek's formula :- 



VA-1. 



rj = viscosity of the continuous phase. 

 Tyi = viscosity of the emulsion phase. 



A = ration of total volume of the emulsoid to the volume of the 

 continuous phase. 



(Zeil. Chem. Ind. Kolloid, 11, 284, 1912) would throw light on the 

 relationship of resin, oil and thinner and also on the composition of 

 the disperse j)hase, although the formula is stated to be inapplicable 

 to organic solvents. Von Smoluchowski {Koll. Zeitsch., 18, 1910, 

 19 IG) does not consider the prospect of deducing such a formula likely 

 to be successful . 



The drying of varnish films is chemically an oxidation process 

 accompanied by increase in weight, volume, and in viscosity during 

 the formation of the coUoid Unoxyn. The rate of drying may at 

 first be rapid, followed by a period of sweating or syneresis. After 

 a time the sweating disappears ; this is possibly a chemical processi 

 connected mth movements in the combined oxygen of the peroxides 

 primarily formed or to changes in the character of the prehminary 

 linoxyn coating. Wolff {Farben Zeit, 24, 1119, 1919) maintains that 

 oxidation and polymerisation proceed at rates depending on the wave 

 length of Ught to which a varnish is exposed. 



It is to the linoxyn that the water-resisting power of varnishes is 

 due. Recently work has been done in connection with the protection 

 of metal and wood parts of aircraft under the auspices of the British 

 Engineering Standards Association, and for the Materials Section of 

 the Technical Department of the Air Ministry. Few resin or resin 

 oil coatings are impervious to water ; possibly Japan lacquer is the 

 best. 



From the writer's unpublished investigations the whiteness of a 

 varnish layer when immersed in water is an emulsion of water in 

 the resin oil mixing as continuous medium. 



An emulsion would be formed if the emulsifying agent ui this 

 case, the resin or oil soap, forms a colloid solution in the non-aqueous 

 solvent (Bancroft, Jour. Phys. Chem., 17, 501, 1913). 



The best water-resisting coatings give an emulsion with difficulty, 

 and although the layer may take up as much as 5 per cent, water, the 

 varnish film wiU remain clear. The conditions are essentially dependent 

 on the nature and concentration of the linoxyn surface layer and on 

 the nature of the oil and rosin together with the electric charge on 

 the metaUic components present in the mixing. It must be pointed 

 out that increased rate of drying of the oil is not sufficient to prevent 

 emulsification. 



The surface layer of a varnish is essentially semi-permeable to 

 water, but not to salts contained therein, e.g., NaCl, K2SO4, KCNS. 



If plain wood be suitably varnished and placed in water absorption 

 will proceed at a rate which varies with the nature of the coating. 

 Professor Lang and the writer have found that for a high class article 



