November 15,1934
I N D U ST R I A L A N D E N G I N E E R I N G C H E M I S T R Y
473
The film is unchanged by ing results, but in the case treatment before test. of most very green films the The test does not deform varnish next to the interor alter the film. face remains tacky, or in the Results are independent nature of a viscous liquid. of rate of a p p l i c a t i o n of Very light loads slowly apstress. plied by hand will strip off The test, being graphic, such films, leaving a thin will show inequalities of adlaver of v a r n i s h o n t h e metal. In such cases not FIGURE 4. APPARATUS SHOWING TEST IN PROCRESS hesion over the length of the sample. As the width of the adhesion but cohesion of the partially dried varnish is measured and testing a t these speeds stripsisdecreased and their number on a single panel isincreased, no doubt gives abnormally high results. The same type of we can to that extent localize areas of varying adhesion. variation was noted by Douglas and Pettifor (8) in their The test is independent of hardness, brittleness, flexibility, study of glue bond strength where their energy-absorption etc. method was used after exposure of specimens to atmospheres LITERATURE CITED of different humidities. This condition offers no difficulty, (1) h Y , u. 8.9 Med. De&, Tentative Specifications, NO. 2248, however, with the thoroughly dried films here discussed, with June 14, 1933. which the separation is clean and speed of test does not in- (2) Christopher, Western G ~8, ~16 ,(1932). fluence the results, a t least within any accuracy of importance (3) Douglas and Pettifor, Third and Final Rept. of the Adhesives Research Comm., Dept. Soi. Ind. Reaearch, England, Appbnin varnish testing. dix 1, p. 5 (1932). Another question of vital interest refers to the relation (4) Hart, circ, 435 (June, 1933). Am. Paint Vsrnish Mfre. between adhesion to aluminum and to other metals. Study is (6) pharmaoopeia,U.s.,loth ~ ~ ~ v vinsi^^,i p. ~128 (1925). 1 in progress with foils of tin, lead, copper, and zinc. Iron and (6) Schmidt, Farben-Ztg., 37, 376 (1931). (7) Schmidt, Z. angezo. C h m . , 46, 625 (1933). steel are of course of first importance, but means have not yet (8) Shaw, T. P. G., private communication to Gardner, “Physical been found for studying them. and Chemical Examination of Paints, Varnishes, Lacquers and CONCLUSIONS The method described meets the requirements of a factory test method as follows: It is reproducible and adaptable to any type of iilm. Films may be dried Or baked under any conditions before
test.
Colon,” p. 220, Inst. of Paint 85 Varnish Research. Washing-
ton, 1933. Reuckeroth, A. w.,and Gttrdner, H. A., SCi. Section Education Bureau, Am. Paint Varnish Mfrs. Assoc., Circ. 323,
(9) Van
p. 155 (1928). RWBXVZD April 18, 1934. Presented before the Division of Paint and Varnish Chemistry at the 87th Meeting of the American Chemical Society, St. Peteraburg, ma., Maroh 26 to 30. 1934.
Stability of Aqueous Solutions of Boric Acid Used in the Kjeldahl Method ABNER EISNERAND E. C. WAGNER Harrison Laboratory of Chemistry, University of Pennsylvania, Philadelphia, Pa.
I
N A RECENT paper [“Titration of Ammonia in F’resence The solution kept in Pyrex glass gave after 197 days a color of Boric Acid,” Meeker and Wagner, IND. ENG.CHEM., not distinguishable from that of the freshly prepared color Anal. Ed., 5 , 396 (1933)l it was mentioned that boric acid standard. The solution kept in lime glass showed no d e solutions suffered deterioration on standing, finally failing to yield a pink color with methyl red. This behavior has now been investigated and is apparently attributable to lack of purity of the distilled water used, revealed by the fact that one lot of freshly prepared boric acid solution was practically neutral to methyl red, the water itself being alkaline. This does not account for the progressive deterioration of other solutions, which could not be studied because none of the water giving such a result was available for examination a t the time its probable responsibility was discovered. A freshly prepared 4 per cent solution of c. P. boric acid in redistilled water was transferred to two bottles, one of lime glass and the other of Pyrex glass, both previously cleaned by steaming out. The fresh solution gave a normal pink color with methyl red under the conditions specified for the ammonia titration. The bottles were kept at room temperature and protected from dust and light. Portions of the solutions were removed at intervals and tested under the conditions of the microtitration: 5 cc. of boric acid solution were diluted with 25 cc. of redistilled water, boiled to remove carbon dioxide, and cooled, 2 drops of 0.05 per cent methyl red indicator were added, and tthe color was com ared with that of a color standard similarly prepared from a Eeshlp made solution of boric acid (using the same lots of boric acid and redistilled water).
terioration for 91 days; after 70 days more, the weakening of the color with methyl red was just visible; after a final interval of 36 days the deterioration was measurable, addition of 0.02 cc. of 0.01 N acid to the test portion being required to equal the color intensity of the standard. At the end of the test period the pH of each solution was determined using a potentiometric titration outfit with calomel half-cell. The two stored solutions and a fresh solution all showed the same. pH. A colorimetric determination of the pH of a fresh 4 per cent solution gave the value 4.1. This demonstration of the stability of boric acid solution, especially if stored in Pyrex glass, removes a possible objection to the boric acid modification of the Kjeldahl method using methyl red indicator. However, the method d e scribed for restoration of solutions deteriorated as kst reported has been used repeatedly and is satisfactory. The necessity for such treatment will probably not arise if boric acid solutions are made with distilled water of the quality ordinarily available in analytical laboratories. RECEIVED June 28,1934.
