I2I that these differences could not be readily and accurately determined from a single reflection.
At about this stage of the investigation this bureau purchased a colorimeter designed and built by Prof. A. H. Pfund, of Johns Hopkins University, on the multiple reflection principle. By means of this instrument the color peculiarities of a paper are determined from three or more diffuse reflections from the paper, and its color characteristics are thus very much accentuated.
The color characteristics were determined by measuring the coefficient of diffuse reflection for red (625 mtu wave-length), green (55 ยฐ m~ wave-length), and blue (460 m,u wave-length) light. The means of getting the three colors of light were three glass filters, transmitting light of the dominant hue as given above, inserted consecutively in the eyepiece tube of the colorimeter, and the diffuse reflection from the paper was matched against the standard for the three colors given.
The color characteristics of twenty-one samples of commercial papers, collected from various sources, were determined, and it was found that all were more or less deficient in the proportion. of blue light reflected, and also that all were deficient, but to a much smaller degree, in the proportion of green light reflected.
The twenty-one samples were also matched for color by unaided eye observation by seventeen individuals experienced in color work. There was practically no agreement, however, among the seventeen individuals as to the " whiteness " of the various papers. This circumstance would thus seem to be an effective argument for the substitution of the Pfund colorimeter for the unaided eye as a means of grading white papers for color.
EMBRITTLEMENT OF MALLEABLE CAST IRON RESULTING
FROM HEAT TREATMENT.'