INDUSTRIAL AND ENGINE ERING CHEMISTRY
238
XCKN OWLEDGMENT
14) Fink, C. G., and Kopp, A. H., Metropolitan Museum Studies,
The researches in connection with the Metropolitan Museum of Art have been to me the most enjoyable of any in my career. Without the inspiration and encouragement of the late Edward Robinson, director of the museum, and of his able successor, Herbert E. Winlock, the investigations would have been impossible. And without the interested and untiring efforts of my assistants, Charles H. Eldridge and Arthur H. Kopp, and the cooperation of my associates, William Campbell and E. P. Polushkin of the Metallurgical Department at Columbia University, the work would not have reached its present state of practical application and actual service. (13)
BIBLIOGRAPHY Chamot, E. M., and Mason, C. W.,“Handbook of Chemical Microscopy,” Vol. 11, Wiley, 1931. Fink, C. G., Metropolitan Museum Studies, 11, Pt. 2, 236-38 (1930). Fink, C. G., and Eldridge, C. H . , “The Restoration of Ancient Bronzes and Other .4110v~,’’ \ f r t r o i m U m Mus~umof Art Bull 1925.
Vol. 26, No. 2
14) ‘l’)
(16)
IV, Pt. 2, 163-67 (1933). Gettens, R. J . , “Technical Studies in the Field of the Fine Arts,” Vol. I, p. 119. Fogg _ _ Art Museum, Harvard Univ., Cambridre. Mass., 1932. Graham, A. K., Univ. Pa. Museum J., 1929, 246. Keiser, H. D., Eng. Mining J . , 130, 163-65 (1930). Lindsley, L. C., “Industrial Microscopy,” Wm. Byrd Press, Inc., Richmond, Va., 1929. Lucas, A., “Antiques: Their Restoration and Preservation,” Arnold, 1924; “Ancient Egyptian Materials,” Longmans, 1926. Marsh, J. E., “Stone Decay and Ita Prevention,” Basil Blackwell, Oxford, England, 1926. Xichols, H. W., Field Museum Nat. History, Museum Tech. Series 3 (1930). Petrie, Flinders, “Arts and Crafts of Ancient Egypt,” A C McClurg & Co., Edinburgh, 1910. Rathgen, Friedrich, “Preservation of Antiquities,” Cambridge, England, 1905. Rorimer, J. J., “Ultra-Violet Rays and Their Use in the Examination of Works of Art,” p. 76, Metropolitan Museum of Art, New York, 1931. Scott, Alexander, “Cleaning and Restoration of Museum Exhibit?,” His Majesty’s Stationery Office, London, 1926. Wainwright, G. A,, “Iron in Egypt,” J . Egyptian Archaeologu 18, 3-15 (1932).
RECEIVED Deceiriber 22, 1933.
Comparison of Constancy of Gold- and Chromium-Plated Analytical Weights HARVEY I-.MOYERAND PAULK. WINTER,The Ohio State University, Columbus, Ohio
I
T HAS been the authors’ experience that gold-plat.ed analytical weights need reconditioning and adjustment every year when used by beginning students. Three sets of new chromium-plated weights were placed in the laboratory and used under the same general conditions as the goldplated ones. After a year in the student laboratory, it was found that the chromium-plated weights were untarnished and had changed in value much less than the reconditioned gold-plated weights.* In the summer preceding the school year in which these tests were made, all the old weights were cleaned and goldplated by a local technician. All weights, including the new chromium ones, were adjusted by one of the authors (Winter) by comparison with a set of Class S weighbs, previously calibrated by the Bureau of Standards. Small lead shot and small pieces of fine aluminum wire were used to adjust the weights until each weight differed from the standard weight, corrected for calibration, by less than the amount shown in the second column of Table I. All weighings were made by the method of substitution on a long-armed Troemner balance which is used frequently in this laboratory for high-precision weighing. Results were reproducible within less than 0.05 ing. After a year’s use in the laboratory the weights were compared again with the same set of standard weights, whose calibration was checked by comparison with another ,set of standard weights just received from the Bureau of Standards. The calibration of the chromium plated weights and of three sets of gold-plated weights selected as representative of fifty sets is included in the tables. The values for the 50- and 20-gram pieces are rounded off to the nearest 0.1 mg. and for the others to the nearest 5 or 0 in the second decimal place. 1 H.H. Willard at the University of Michigan has informed the authore in a private communication t h a t he has become convinced that chromiumplating is superior to gold-plating for analytical weighte.
All the chromium-plated weights were close to their adjusted values, whereas most of those plated with gold were seriously in error. It seems particularly significant that one chromiumplated 10-gram piece in set A, an old weight plated with chromium as an experiment several years ago, was within the tolerance of its adjustment and that its gold-plated companion was 0.40 mg. in error. TABLEI. CALIBRATION O F GOLD AND CHROMIUM-PLATED WEIGHTSAFTER ONE YEARIN STUDENTLABORATORY PRECISION NOMISALO F AD- ~-GoLD-PLATED---VALVE J c s n m N r Set A Set B Set C 50 20 10 10 5 2 2 1 1 1
’‘ b C
M Q.
0.1 0.1 0.05 0.05 0.05 0.05 0.05
f0.4 f0.4 +0.05” 4-0.40 +0.10 0.00
0.05
-2.20b 0.00 +0.10
0.05 0.05
....
+0.6 +0.6 10.30 10.20 +o. 10 +O. 30 +0.30 +0.20
.... ....
Ma. +0.7
+1.3 +0.20 +o. 20 f 0 . 10 +0.05 0.00 +O. 05
.... ,...
-CHROIIUJd-PLATED-Set D Set E Set F
M Q.
Ma.
MQ.
-0.2
-0.2 +0.1 -0.15
0.0 f0.1 -0.06 -0.05
-0.20b 0.00
t0.05
+o. 1
-0.05
-0.10 -0.05 0.00 0.00 0.00
....
....
-0.10
o.ooc
0.00
....
0.00 0.00
....
....
....
,...
Chromium-plated. Stem loose Stem nut
A comparison of the two kinds of weights after a year’s use suggested that the superiority of the chromium was due t o its greater resistance to scratching and abrasion. The corrosion of the brass where the gold had worn off would explain the positive errors among the gold weights. The weights were given a severe test, since 50 sets were used by approximately 175 beginning students throughout the year. It is probable that heavily plated gold weights would have remained more nearly constant in value than these reconditioned gold-plated ones, but it is not probable that they would have excelled the much cheaper chromium-plated weights. RECEIVIPD September 2, 1933
