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Les diagrammas suivanta illuatrent la mAthoda. 1 2 3 1 2 3 4 5 6 = ^ :::n-.'3aiS!iaiHiH Color App the ..,,,|,,.!,,.,,,,,,,,,„5,,,,.,„,,,,,,,,,„,,,,,j„ ,,, j^^ M.i.i,,|.,„i„.,j„„i.,„i„„j„>„„i„„i;„,=|„,^,^||Jiiij|i! ism-ga'giMSJgiggaaasjiiamaiSg Color Measurement, and its Application in Medicine and the Arts. BY CASEY A. WOOD, M.D. Oft THOMAS A. WOODRUFF. taine imniher of units in the other two scales, so that ajxin combinations of ecjual units of any two or of the three a color nomenclature is founded which consists of eight funda- mental terms by means of which every possible color can be first measured and theti described. The instrumf nt consists essentially of a double, parallel-sided, wooden tube, ending' in an eye-piece at one end, and equal apertures for viewing the color to be measured and for the glasses used as measurers at the other end. Provision is made for the equal illumi- nation of the color to be measured and the standard white or reflector from which the light is conveyed to the comparison tube; and also for the easy adjustment of the gla.sses used in the measure- ments. The mechanism also avoids the side lights (falling on the eyes) which often render the critical estimation of color under ordi- nary conditions of observation absolutely impossible. Both fields of view are evenly illuminated with indirect sunlight. When this is effected, either side can be used for the standard white without affecting the measurement. The colored light from the object to be measured is transmitted through one tube, and the light from a standard white through the other; this standard white light is then intercepted by the graded color glasses until it corresponds in color to the object to be meas- ured, when the numerical color value of the glasses used can be read off. I append a desciiption of the accompanying cuts, from I,ovi- bond's book: "A longitudinal section of the instrument is shown in Fig. 2, which consists of a rectangular tube about ten inches long, divided Fig.lL in the middle by a taper partition, B, terminating in a knife-edge at the eye-piece C, the aperture of which it divides into two equal parts. This cell is represented crosswise in aperture. "At the other end are two openings, A, A, which admit two equal but separate beams of light to the eye-piece in such a manner that, on looking through it, the eye commands a simultaneous dis- tinct view of both openings. The knife-edge of the partition, being inside the range of vision, does not disturb this distinctness of view. COLOR MEASUREMENT The grooves, D, D, are intended to receive the graded sHps of colored glass for intercepting the beams of light transmitted through the tubes before reaching the eye. ' ' The opening at I'^ is intended to receive the gauged vessel containing the colored liquid to be nieasured. "Fig. 3 represents the instrument as arranged for measuring color in liquids up to two inches in thickness. The optical instru- ment, D, slides into the upright stand at A, to receive the gauged cells at H on either side. Light is taken from the standard white reflector, D, on st d D B C, for transmission through the tubes to the eye- piece. COLOR MEASdREMEN'l "A separate stand is required for cells which are longer thai- two inches. The niethorted by a separate stand, K, which can be moved to accommodate a tul)e of any length. The reflector, I), is u.sed as in Kig. •?. "Fig 5 shows the arrangement for measuring color in opaque objects. The optical instrument, B, is here shown as a binocular, but the monocular described in Fig. 3 fits equally well into the shoe A , the bottom of which is commanded by both tubes of the instru- ment. Under one side, at F, is placed the opaque substance to be measured, and under the other the standard white (pure precipitated lime sulphate pressed to an even surface) for reflecting the beam of white light, which is then intersected at J by the suitable standard glasses, as already described for transparent colors." At my request the inventor of this valuable instrument has measured a number of pigment samples selected at random from the stock of a large American color and paint manufacturer. I give the results in a few cases: The paint sold under the name of "prim- f rose 'was found to contain 1.16 red units, 2.9 yellow units, and .04 ofablueumt; the so-called "sahnon " color equals 1.3 units of red, • j 2.7 of yellow, and 1.5 of blue; "llac" equals red 1.85, yellow 1.7, | and blue 3 units; ' ' green stone ' ' is composed of red i . 3, yellow 27 * andblue 1.5 units; " apple blossom " is composed of red 1.9, yellow J .95. blue .8; " light blue " is composed of red .95, yellow 1.2, blue I 4.9; ^cream" comprises red 1.25, yellow 2.5. blue .04; "yellow stone, red 4.3, yellow 3.4, blue 1.5; "dark drab," red 6.2, yellow I 7. blue 7; "extra light" drab, red 1.25, yellow 1.35, blue 2.8; golden brown." red 7.4, yellow 7.4, blue 3.2 8 COLOR MEASUREMENT I would suggest that in giving the composition of a color we write it like a chemical formula: for instance, "golden brown" might be indicated as follows, R7.4Y7.4B;,.2. As L,ovibond* points out, many of these formulas are capable of reduction to simpler terms, but for all practical purposes it is, perhaps, as well to speak of them in terms of the primary colors accepted as standards. The purposes for which the tintometer is now used are numer- ous and embrace almost every department of the arts. A few of these may be mentioned: It has been found that the amount and kind of adulteration in most foods and commercial products, as well as the impurities com- monly found in drinking-water and other fluids, can be determined by the deviation, measured by the tintometer, from the normal tint of the pure article. Instead of making a laborious and complicated chemical examination of the suspected compound, its color value is determined in a few minutes. Such a chromometric examination is usually found to answer all the purposes of a quantitative analysis. In this way the tintometer is now employed in England, and to some extent elsewhere, by all sorts of conmiercial houses, and it is also used with great success by the health departments of cities for the ready detection of impurities and adulterations in milk, water, beer, and other foods. The slightest departure from purity, whether in food or any other product, is at once shown by a measurable and corresponding variation in color. The substitution of an exact color measurement for a chemical analysis is not new in physics. For example, the Bessemer process of converting iron into steel is almost entirely regulated by color changes observed in the furnace flame. It is exactly on this principle, except that the examination is made leisurely, that in a mixture or solution any departure from the standard, both as to kind and amount, is estimated by this instrument. When an exact color measurement has been made of a certain product (it matters not whether it be liquid or solid), the tintometer very readily shows whether a commercial sample is of equal purity. To a limited extent chromometry has also been made use of for diagnostic purposes in medicine. In urinary analysis we have the Vogel scale of colors, where variations from the tint exhibited by normal urine are intended to indicate something of the chemical composition of that excretion. The best example, however, of the use of a chromometer as an aid to medical diagnosis is the hemoglobinometer, by which color- ♦ Measurement of tight and Colour, p. 39. changes in certain im] normal bloc blood unde it correspoi exactly con blood. In which I ia urer of abnc Gower's to exact chron in 1885. H the shade o movement i under exam off the side ment for chr The att Fleischel ins I/Ovibond's € ored glass," in glass of \ ground and vessels were arranged to right-angles line to read color match \ the thickness liquids prove "An inci concerning th ing colors, o\ without a bre to arrive at blending, wa; person may i point by the entirely to re standards; th( ard-glass slip minute shades- i^^mvw^pn COLOR MEASUREMENT "^ changes in the blood, pointing to an excess of or a diminution in certain important constituents, are measured by reference to a normal blood color taken as a standard. In Gower's instrument the blood under examination is diluted with water, drop by drop, until it corresponds in color to that of a tube of red fluid assumed to exactly correspond in shade with a one-per-cent. solution of normal blood. In practice this little instrument presents several defects, which I intend, later on, to point out. A more pretentious meas- urer of abnormal blood, and one which conforms more closely than Gower's to those conditions that have been found necessary for exact chromometry, is that of Fleischel von Marxow, first patented in 1885. Here the blood is compared with a standard ruby glass, the shade of which is increased or diminished by a simple screw movement until it corresponds in color with the blood mixture under examination. The absence of any arrangement for cutting off the side lights appears to me to reduce the value of this instru- ment for chromometric purposes. The attempt to compare the standard glass now used in the Fleischel instrument with blood samples is beset with difficulties, lyovibond's early experiments {loco cii., p. 14) showed this. "Col- ored glass," he says, " was next tried, and long rectangular wedges in glass of different colors, with gradually graded tapers, were ground and polished for standards, whilst corresponding tapered vessels were made for the liquids to be measured. These were arranged to work, at the end of the instrument, up and down at right-angles before two apertures, s^de by side, with a fixed centre line to read off the thickness of each before the aperture when a color match was made; but here also the difference of ratio between the thickness and color depth of the different colored glass and liquids proved fatal to the method. "An incidental observation was made during these experiments concerning the difficulty of arriving at a final judgment with taper- ing colors, owing to one shade gradually blending into the next without a break of any kind to arrest the vision. The mental effort to arrive at a decision, under these conditions of gradual color- blending, was troublesome and vexatious in the extreme. Any person may realize this difficulty by attempting to fix a definite point by the vision in a graduated color line. I was enabled entirely to remove the difficulty by using separate glass slips for standards; the line of color decision made by each additional stand- ard-glass slip used being a precise definition between the most minute shades. ' ' 10 COLOR MEASUREMENT I am myself now engaged in experimenting with a hemometer, constructed on the same lines as the tintometer, which I shall intro- duce to the profession shortly if I find it of any especial value. A rather curious application of the tintometer has been made in a certain Agricultural Experiment Station where the value of fertil- izers under examination is determined by the change in color pro- duced in the leaves of certain plants whose growth was used as a test. The degree of dryness, as well as the amount of yellow, in samples of white lead, can be accurately measured chromometri- cally, while the analysis of natural waters is after a few trials made exceedingly simple, from the fact that the amount and kind of impurities in them bear a fixed relation to their color. So it is with flour, glucose, indigo, annatto, lard, butter, chlorophyll, steel, petroleum, wine, glycerin, and a hundred other articles of every- day production. But quite apart from these practical applications of a color- measure to medicine and in the arts, it is to be hoped that some universal chromometric standard will finally be adopted, and so there will be added another to that long list of sciences whose technology is, in the widest sense, the common property of all scientific men. Editorial in f r) i.s so te 01 bv all Editorial in Fthruary Cleveland Journal of (Medicine ) rm«Sliii,Si^^SM«i ii*SiaSfiWiiS2£i3Ei •#llSKM^*?-.-«;ftji*ii»iSi-'