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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...

NOTES 45 1 formatioqa could not be brought about through the conventional halogenation of the acyl group with subsequent condensation with an amino compound.The melting point of the ethyl DL-dipalmitoxypantothenate thus prepared was 61.5-63.0' in comparison with 57.0-58.5' for the same compound prepared by the in situ palmitoylation of ethyl DL-pantothenate.2 Upon single dose assay with rats,4 the newly synthesized ethyl DL-dipalmitoxypantothenate was found to be fully active as a source of pantothenic acid. EXPERIMENTAL Ethyl ~~N-In,r-dipalmitoxy-p,p'-dimethylbutyryl] paminopropionate (ethyl DL-dipalmitoxypantothenate). Slx hundred twenty-five milligrams (1 mmole) of DL-dipalmitoxypantoic acid2 was dissolved in 40 ml. of dry pyridine which contained 200 mg. (excess) of ethyl p-alanate and 208 mg. (1 mmole) of dicyclohexyl carbodiimide. The clear mixture was set aside a t room temperature for 96 hr. The precipitate was removed by filtration, and the filtrate was evaporated to dryness under reduced pressure. The residue was taken up into ether, and washed with I N hydrochloric acid, a cold 57, potassium carbonate solution and with water. After drying over anhydrous sodium sulfate, the solvent was removed and the residue recrystallized twice from 95% ethanol. Yield: 540 mg. (74.6%), m.p. 61.5-63.0".

No abstract

Baked alkyd urea-formaldehyde coatings pigmented with titanium dioxide can b e varied from high to low gloss. Contraction of the film on cooling produces surface irregularities above flocculated particles, with a resulting loss of gloss. In the test system gloss is increased by the formation of surface active salts from the acids of the alkyd. It is suggested that the cation of this salt is adsorbed within the water layer present as an adsorbed film on the pigment surface. This cation confers a positive electrical charge on the pigment, while the high molecular weight anion serves as counterion. This explains the gloss increase obtained b y treatment with appropriate basic agents, particularly alumina hydrate, or by increase in relative humidity, and also the gloss decrease caused by low molecular weight acids having a strength equal to or greater than that of the alkyd acids.LKYD urea-formaldehyde enamels pigmented with titanium A dioxide can be prepared to yield baked coatings varying in appearance from essentially a matte to a high-gloss finish without change in pigment-volume concentration. The desire to understand the phenomena involved prompted this study of both the mechanical and the colloid chemical aspects of gloss development.After standard procedures for preparing, applying, and baking the finishes had been developed, consideration was given to the influence of the alkyd and urea-formaldehyde vehicles, and of the titanium dioxide pigment. Through electron microscope, hiding power, and electrophoresis studies it has been possible to develop a hypothesis relating the gloss results to vehicle interaction with the pigment causing it to cluster. This in turn is related to the nature of the ionic double layer a t the pigment surface. This hypothesis has suggested an experimental approach emphasizing the nature and strength of the acids of the alkyd vehicle and their interaction with the pigment to yield ions that form the ionic double layer. Modified potentiometric procedures have been developed for these studies. Experimental ProcedureThe conditions chosen for the preparation of the films, in particular the alkyd selected from a number of commercial vehicles and also the details of dipping and baking the panels, were designed to yield large differences in gloss between films, thereby simplifying the interpretation of the results.