November 15,1934
I N D UST R I AL A N D E N G I N EE R I N G CH E M I ST R Y
In case of a complete obliteration method as described in this paper, a decrease in the ultimate brightness of a paint results in higher hiding-power value figures, as observed a t visually complete contrast obliteration. This effect of decreased brightness has been previously demonstrated by Pfund (S), Gardner (g), and Rhodes and Fonda (9). Morrison (6) found that there was an increase in the hiding power of a paint when raw linseed oil was substituted for refined linseed oil. This was ascribed by him to the presence of coloring matter in the raw oil; obviousIy it was due to the decreased brightness of the paint. T h e interdependhiding value is illustrated in Figure 3. A practical linseed oil paint of 90 per cent ultimate brightness was reduced in brightness successively to 84 and 78 per cent by the addition of a coloring
395
EVALUATION OF PIGMENTS FROM HIDING-POWER VALUES For the purpose of comparison, hiding values of paints of 28 per cent pigment volume concentration were selected for composite pigments because this concentration is considered standard in pigmentation of most linseed oil paints. On the other hand, zinc sulfide and titanium dioxide are used a t low pigment concentration only, and were therefore compared on the basis of 15 per cent pigment volume concentration. Hiding-power values determined by the authors are as follows (Figure 2):
TABLE11. HIDINGPOWER VALUES 28 PER CENTPIQMENT VOLUMECONCENTRATION Lithopone Titanium barium pigment High-strength lithopone Titanated lithopone Titanium calcium pigment 15 PER CENTPIQMENT VOLUMECONCEITRATION Zi,nc sulfide Titanium dioxide
HIDINQ POWER Sq. ft.llb. 43 58 67 67 74
10s
180
Hiding-power values a t pigment concentrations other than those given above may be readily obtained by drawing a vertical line through hiding-power curves a t any desired pigment concentration. (It is interesting to note that the hidingpower relations of various pigments shown above are consistent with those obtained by Hallett, 3.)
ACKNOWLEDGMENT Acknowledgment is due to Jos. L. Turner, director of research, and D. W. Robertson, sales engineer, both of the Titanium Pigment Co., Inc., for their valuable help and suggestions in the preparation of this paper.
LITERATURE CITED (1) Bruce, H. D., Bur. Standards, Tech. Paper 306 (1926).
Gardner, Sward, and Levy, Am. Paint Varnish Mfrs. Assoc., Sci. Sect., Circ. 362 (1930). (3) Hallett, R. L., Proc. Am. SOC.Testing Materials, 30, Part I1
(2)
(1930).
G.S., IND.ENG.CHEM.,Anal. Ed., 2,69 (1930). Kraemer and Schupp, Jr., “Determination of Hiding Power of White Paints,” presented before the 85th Meeting of the American Chemical Society, Washington, D. C,, March 26 t o 31, 1933. (6) Morrison, R.A.,OiKcial Digest Fed. Paint & Varnish Prod., 112,
(4) Haslam,
(6)
t h o u g h t h i s influence can be clearly traced even a t comparatively low pibment concent r a t i o n s , it manifests itself in a most pronounced manner
8
‘
po
f
$ a
745 (1932).
(7) Pfund, A. H., Am. Soc. Testing Materials, Tech. Papers 30,878 +-
(1930). (8) Pfund, A. H., J. Franklin Inst., 196,69 (1923). (9) Rhodes and Fonda, IND.ENQ.CHEM., 18, 130 (1926). (10) Sawyer, R. H., Ibid., Anal. Ed., 6 , 113 (1934). (11) Sawyer, R.H., “A Method for Measuring the Hiding Power of Dry Paint Films,” presented before the 86th Meeting of the American Chemical Society, Chicago, Ill., September 10 t o 15. 1933. RECEIVED April 28, 1934. Presented before the Division of Paint and Varnish Chemiatry a t the 87th Meeting of the American Chemical Society, 8t. Peteraburg, Fla., March 26 to 30,1934.
STARCH FROM WASTESWEETPOTATOES MAYFINDUSE IN PAPER INDUSTRY. According to the results of experimental tests made by the Bureau of Standards sweet potato culls offer some possibility as a source of starch for sizing paper and for paper adhesive. The culls constitute a huge waste in the southern states, and the Bureau of Standards and the Bureau of Chemistry and Soils are jointly endeavoring t o find ways of profitably using them. Corn starch and cassava starch are used extensively in book pa ers to improve their printing quality. The Bureau of Standar& made and tested wood-fiber book papers sized with these starches and with sweet potato starch and the latter compared very favorably with the others.
