HYSICAL tests (6) have established that pronounced structural changes may occur in paint films during ex-P terior exposure. Many of these changes can be ascribed only to chemical reactions between pigment and the vehicle, but none of the products have been definitely identified, even in the case of simple systems. Investigators have assumed (1,4,10) that when basic pigments were present, soaps were formed. No data have been previously obtained, however, to prove that this is true, although evidence of saponification (8) and the effect of the acidity of linseed oils upon paints containing different basic pigments (3) is such as to suggest that these general assumptions are correct. This paper describes a study of certain zinc oxide paints and zinc oxide-oleic acid mixtures which demonstrated that the pigment can react with the vehicle under certain conditions. The products were isolated and identified in the case of the simpler systems consisting of zinc oxide and oleic acid.Paint films containing zinc oxide as the only pigment rapidly become hard and brittle upon exterior exposure. This marked change in film structure was observed by one of the authors in a study of the flexibility of zinc oxide paint films. In this study (6) the paints were prepared by dispersing 24 per cent of zinc oxide by volume in a linseed oil having an acid number of 4. The paint contained the usual proportion of a commercial leadmanganese-cobalt n a p h t h enate drier. Films which were 0,003 inch thick were applied to tinned copper panels by means of a pair of shims and a straight edge used as a draw knife, and when dry they were exposed on a vertical fence facing south a t Sayville, Long Island. Portions were cut from the panels after 1-day, 3-week, and 5week exposure periods. The films were loosened from the metal by running mercury around the edges of the panels and allowing it to a m a l g a m a t e with the tin. This permitted removal of the s l m s without subjecting them to any unusual stress or otherwise affecting their WILLIAM HOWLETT GARDNERPolytechnic Institute, Brooklyn, N. Y. physical state. The films were then conditioned for 24 hours a t 75' F. (23.9' C.) and 50 per cent relative humidity just prior to testing. The test consisted of bending the film over mandrels varying in size from */16 to 3/8 inch in diameter in steps of 1/16 inch.The films exDosed for 1 dav could be readilv flexed over a 1/16-inch mandrel without rupture, whereas the films which had been removed after 3-week exposure could not be bent over the largest mandrel (3/8 inch) without breaking. The films exposed for 5 weeks readily broke between the fingers upon the slightest bending. These tests indicated that the films had become hard during this short exposure and that a t least some of the ingredients were transformed in such a way as to modify the internal structure of the film. MICROSCOPICAL STUDIES. Some idea of what may haveoccurred was obtained by observing slides of various dilute mixtures of zinc oxide and linseed oil with the aid of the microscop...

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All methods that have been suggested for the preparation of thiocyanogen solutions involve the use of strictly anhydrous solvents, since the presence of moisture causes rapid hydrolysis and decomposition to take place. It is possible, however, to stabilize thiocyanogen in aqueous solution to a limited extent by the presence of large quantities of potassium thiocyanate.Thiocyanogen has been prepared by the action of iodine upon an ethereal suspension of silver thi0cyanate.l This reaction does not go to completion, since thiocyanogen is a halogenoid2 lying between bromine and iodine in order of chemical activity. It can be prepared by the oxidation of a solution of hydrogen thiocyanate in ether with manganese dioxide. The electrolysis of thiocyanates in alcoholic solution results in the discharge of the thiocyanate radical and the formation of thiocyanogen as an anodic p r~d u c t .~ The interaction of plumbic acetate and thiocyanic acid in ethereal solution presumably results in the formation of plumbic thiocyanate which immediately decomposes into thiocyanogen and plumbous thio~yanate.~The action of bromine upon various metallic thiocyanates gives thiocyanogen in better yield, but few solvents yield

spaces as being continuous, anymore than we would necessarily expect them to be in the solid phase of a jelly. Undoubtedly a few of the channels have external openings on both sides since some varnish films show a definite porosity (1, 2, 3, 5, 8,9), but it is clear from the studies made that the pores which do exist are usually extremely fine (1). Swelling by various liquids may, however, produce a permanent increase in permeability since varnish films would be of the elastic type of gels. The adsorptive forces involved when a liquid or vapor