280
IKDUSTRIAL -4XD ENGlNEERING CHEMISTRY
minimize the fluctuations in the take-off pressure, tube B should be as small as is possible without permitting entrainment of the mercury in the exhaust gas. (If desirable, a plug of cotton or glass wool may be inserted in tube C below the exhaust to prevent passage of entrained mercury.) The surface of the mercury in the outer container should be large, so that its level will not vary appreciably with changes in level b. For a moderate gas stream, standard Pyrex glass tubing having the following outside diameters was used satisfactorily: A , 7 mm.; B, 15 mm.; C, 10 mm. A 500-cc. Erlenmeyer flask or ordinary bottle may serve as the container.
VOL. 10, NO. 5
tubes are necessary, a leveling bottle connected t o the outer reservoir may prove advantageous in permitting operation under various pressure conditions.
Literature Cited dskey, J . Am. Chem. Soc., 52, 970 (1930). Balm, 2. Elektrochem., 38, 868 (1932). Green, ISD. ESG. CHEM.,Anal. E d . , 8, 40 (1936) Hein, Z. ungew. Chem., 40, 846 (1927). Lux, 2. anorg. a22gem. Chem., 226, 21 (1935). (6) Sickel, Chem.-Ztg., 50, 926 (1926). (7) Stock, Ber., 47, 3103 (1914). (8) Zbzd.. 58B, 2058 (1925) (1) (2) (3) (4) (5)
Obviously, the dimensions may be varied as necessary, glass inner seals may be used in place of the rubber connections, and liquids other than mercury may be used if desired. I n some applications where permanent seals between the glass
KECEIVEDS o p e m b e r 1 2 , 1 9 3 i
Preparing Fragile Paint and Varnish Films For Determination of Tensile Strength, Elongation, and Permanent Set ERNEST H. B A l O R h m LEO IL-IMPF City of New York, Laboratory of the President nf the Borough of Queens. Long Island City, N. Y . ~~
S
EVERdL physical properties of paint and varnish filnis,
such as toughness and elasticity, have usually been determined only indirectly. Reduction with kauri, exposure and weathering tests, etc., are not always suitable for evaluating such properties. Preparation of the free film in a forin which permits handling makes possible a direct examination of its properties. Two methods of preparing free filnisstripping from the foundation (3) or dissohing the foundation with acid (1) yield films which may be tested in extensiometers such as t h a t of Gardner ( 2 ) or Tesson (4). For stress-strain measurements Kelson (3) prepared paint and varnish films by spraying or flowing on amalgamated tin plate (stating t h a t brushing does not give satisfactory films unless t,he material has a sufficiently low yield value to permit brush marks to flow out). His films were 0.120 to 0.150 mm. thick for paints and 0.090 to 0.100 mni. thick for varnishes, about ten times the thickness usually found in practice. Furthermore, he had difficulty in obtaining films of uniform thickness. Most paint and varnish films are too t'liin, too soft, or too brittle to be handled by Selson's method. In the authors' method, the free film is prepared on a thin tinfoil foundation, enabling the operator t o handle it easily until the test specimen is placed in the extensometer. There the test piece floats upon a bath of mercury which removes the tin-foil backing by amalgamation, leaving the free film in place for testing. The film is made by pouring the material to be tested on a sheet of tin foil (0.001 cm. thick). T o obtain a uniform film and t o keep any material from reaching the back of the foil, which
TABLE I. DETERMINATIONS Film
Material
Age of
Film
Thickness
Days
Cm.
Maxi- PerTotal mum maBreak- Elonga- nent ing Load tion Set Grams % %
Spar varnish, federal specifi35 cation TT-T-12la 60 0 0020 Raw linseed oil, with 5% 6.5 liquid driers 10 0 0015 Floor varnish, federal speciBcation TT-T-71 68 0.0026 74 4 0 Vehicle of fiat ceiling paint" F8 0 0015 0 Vehicle obtained by permitting pigment t o settle.
+
17
,.
20
19
0 30
0 30
would later prevent the amalgamation of the tin, the coated foil is hung from a 3.2-mm. (0.125-inch) horizontally fixed metal rod to which it is attached with paper clips. A similar rod is attached f the foil and left free, thus kceping the panel 0th. After drying, the test piece is cut so that right angles t o the direction of f l o r ~of the material. In any ot,her direction there will usually be an appreciable variation in film thickness. B template in the form of the test piece is helpful in cutting the specimen and marking it for elongation measurements. Two holes, 40 mm. apart, are drilled in it and carbon black is rubbed gently over the holes to get the elongation marks on the film. The apparatus for testing is a horizontal extensometer. The test piece floats upon mercury in a shallow dish ( 5 mm. deep, 40 mm. wide, 250 mm. long). The ends of the test piece are gripped by folded emery paper held in position with paper clips. One grip is attached to a stationary support by a thin rubber band. The other is attached by a strong thread passing over a pulley t o a light pan. The top of the pulley is on a level Rith the surface of the mercury. About half an hour is sufficient for amalgamation and then weights can be applied and measurements made. The progress of the amalgamation is usually visible. Some determinations by this inet'hod are given in Table 1.
Discussion Characteristics of paint and varnish films, the influence of age, humidity, and temperature, or the effect of new ingredients or a neK procedure of production can be studied by this method. It offers a means for evaluating tough and elastic films, such as those called for by federal specification TT-P-5la and others. This method can be used where the kauri reduction test is inapplicable because of incompatibility of the kauri solution and the vehicle of the material to be tested.
Literature Cited (1) Bayor and Kampf, I K D .ENG.CHEY.,Anal. Ed., 9, 49 (1937). (2) Gardner, H . A,, "Physical and Chemical Examination of Paints. Varnishes, Lacquers, and Colors," 6th e d . . p. 1003, Washington, Institute of Paint and Varnish Research, 1933. (3) Selson. H . A,, Proc. .4m. SOC.Testing Muterials, 21, 1111-34 (1921). (4) Tesson, F., Researches et inventions, 17, 189-202 (1936). RECEIVED January 19, 1938.
