APPENDIX E. REPORT ON SUGAR DETERMINATIONS. [CORRESPONDENCE.] YALE COLLEGE, New Haven, Conn., December 30, 1887. SIR: I have the honor to transmit to you herewith a report on certain standard quartz plates used in the classification of sugars for duty, made by a committee of the National Academy of Sciences, in compli ance with the request, contained in your communication of June 17, 1887. Very respectfully, O. C. MARSH, President of the National Academy of Sciences. Hon. C. S. FAIRCHILD, TREASURY DEPARTMENT, Washington, D. C., June 17, 1887. GENTLEMEN: Certain questions connected with the classification of imported sugars are now under consideration by this Department. It becomes necessary that three standard quartz plates used by appraisers in determining the saccharine strength of sugars whereby its classifi cation for duty is made, be tested with a view to ascertain their exact measurement, angle, and ray. I will thank you to inform me if the necessary test can be made by your Academy, and, if so, upon receipt of your reply, the plates will be forwarded to such address as you may indicate. Respectfully, yours, The NATIONAL ACADEMY OF SCIENCES, C. S. FAIRCHILD, Secretary. Washington, D. C. YALE COLLEGE, New Haven, Conn., June 28, 1887. SIR: Your communication of June 17, inquiring if the National Academy of Sciences would undertake the examination of the standard quartz plates used in the classification of sugars for duty, reached me to-day. In reply, I have the honor to say that the Academy will undertake the proposed investigation, and I have appointed Prof. A. W. Wright, of Yale University, to superintend the work. If you will have the plates forwarded to him at New Haven, Conn., the investigation will be com. menced without delay. Very respectfully, O. C. MARSH, President of the National Academy of Sciences. Hon. C. S. FAIRCHILD, YALE COLLEGE, New Haven, Conn., June 28, 1887. SIR I inclose a communication from the Secretary of the Treasury, dated June 17, 1887, inquiring if the National Academy of Sciences would undertake the examination of the standard quartz plates used in the classification of sugars. I have informed the Secretary that the Academy will undertake the proposed investigation, and I have requested him to send the plates to you, whom, as chairman of the committee, I have appointed to superintend the work. Your colleagues in this investigation will be Prof. Edward S. Dana, and Prof. Charles S. Hastings of Yale College, and it will be a favor to the Department if you can complete the examination at an early day. The proper province of the National Academy is not merely to make a technical examination in a case of this kind, but, likewise, to bring out the scientific principles involved, as a basis for future use, and with this idea in view, I hope you will be able to undertake the work. Very respectfully, O. C. MARSH, President of the National Academy of Sciences. Prof. A. W. WRIGHT, NEW HAVEN, CONN., December 29, 1887. SIR: The committee appointed by the president of the National Academy of Sciences, at the request of the honorable Secretary of the Treasury, to examine certain quartz plates used in the laboratories of the United States appraisers' offices in Boston, New York, and Philadel phia, respectfully report that they have completed the examination and measurement of these plates, and submit herewith the results obtained by them, together with an account of the methods employed, and of the instruments and processes made use of in the different stages of the work. Very respectfully, your obedient servant, Prof. O. C. MARSH, ARTHUR W. WRIGHT, Chairman. President of the National Academy of Sciences. REPORT. The committee have made an examination of six quartz plates sent to the chairman by order of the Secretary of the Treasury, from the ap praisers' offices of Boston, New York, and Philadelphia. The plates are used in adjusting the saccharimeters employed in the determination of the saccharine strength, or degree of purity, of imported sugars, upon which depends the classification of such sugars into different grades for duty. The use of the saccharimeter is founded upon the property of cane sugar, that when a ray of plane-polarized light is passed through a solution of it, the plane of polarization of the ray is turned to the right, and the angle through which the plane is turned in a column of the solution of given length is proportional to the strength of the solu tion, or, in other words, to the amount of sugar contained in it. The same property is found in quartz, for a ray transmitted through it in the direction of the crystalline axis, and the variety of quartz known as right-handed, turns the plane of polarization to the right, and the amount of the turning for light of different wave-lengths, or the dispersion, is very nearly the same as for cane sugar, and is proportional to the thickness of the crystalline plate. Each plate bears a number representing the exact percentage which a column of sugar solution of a certain length bears to a standard sugar solution of the same length under certain standard conditions, when it rotates the plane of polarization to the same degree as the quartz plate. Hence, when placed in the saccharimeter, it may be, and is, used to determine the exactness of the scale of the instrument, or for adjusting it when not properly set. As an error in the setting affects all subsequent measurements made with the instrument, the importance of a correct determination of the exact value of the quartz relatively to a standard sugar solution is evident. L.-DESCRIPTION OF THE QUARTZ PLATES. Of the six quartz plates, three were received by the committee early in July, and these bore the numbers 51.5, 99.1, and 99.1-2. During the first week of September, three others were received, bearing the numbers 50.8, 96.0, and 98.8. In the following paragraphs, they are desig nated by the numbers simply, and in the order of their numerical value. No. 50.8.-This was a portion of a broken plate, and was in three fragments, the largest of which comprised the central portion of the plate, and was amply sufficient for the examination. It was simply mounted loosely in an ordinary sugar tube. The number was marked upon the end of this tube. No. 54.5.-A circular plate, 15 millimeters in diameter, mounted in a blackened brass tube, 30 millimeters in diameter and 38 millimeters long. At about the middle of one side of the tube, a short brass pin, or plug, was inserted, the mark number being engraved in the metal near it. No. 96.0.-A circular plate, 15 millimeters in diameter, mounted in a polished and lacquered brass tube, about 125 millimeters long, and having at each end a flange of the same diameter as that of an ordinary sugar tube, for supporting it in the proper position in the saccharimeter. The number is marked in the flat surface at the end of the tube where the plate is inserted. No. 99.1.-A circular plate, 15 millimeters in diameter, not mounted. The value 99.1 is not marked upon the plate, but was communicated to the committee in a letter from the appraiser. No. 99.1-2.-A circular plate, mounted like No. 96.0, having substan. tially the same dimensions, and marked upon the end surface in the same manner. No. 98.8.-A circular plate of the same size as the preceding, mounted in a rather heavy brass tube, which was polished and lacquered. The tube, 30 millimeters in diameter and about 125 millimeters long, has a pin on one side, like No. 54.5. The mark is scratched upon the end surface of the tube. II.-THICKNESS OF THE PLATES. The thickness of each of the quartz plates was measured with a spherometer with great care. Independent series of measures were made by two members of the committee with substantially identical results. They are given herewith, and may be considered accurate to the thousandth part of a millimeter. They represent the thickness at the center of the plate, which is approximately the mean thickness of the whole plate: The rotation of the plane of polarization by a quartz plate of given thickness, cut perpendicularly to the axis, has been determined with great precision by several different physicists. Mascart,* from a series of very accurate measures, deduces the value 210.73, for the angle of rotation of the plane of polarization for the rays from a sodium flame, for a thickness of 1 millimeter, and states that this value is correct to one part in two thousand, or one unit in the last decimal place given, at the temperature of 15° C. Govet and Sarasin † give the value 210.727, for 20° C. Von Lang‡ found the value 210.727, at about 21° C. These observations were made with long columns of quartz, and the results may be accepted as correct. The number 210.73 may be taken as the most accurate value for 20° C. The direction of the ray in all these experiments was very accurately parallel to the crystalline axis. For thinner plates, of from 1 to 2 millimeters in thickness, the com. monly accepted value, for 20° C., is 210.67 per millimeter,§ which is founded upon the determination made by a number of different observers. The difference is perhaps due to a change in the constitution of the substance of the crystal near the surface, made in polishing, or, more probably, to the fact that these plates will rarely, if ever, accurately fulfill the conditions of perfect parallelism of the surfaces and perpendicularity of the crystalline axis. The number is probably too small, but, as will be mentioned further on, these thin plates give different values according to their position. Were the rotation of the ray strictly proportional to the thickness of the plate, its value could be readily deduced from the measurement of the thickness by the use of the above data. As they were found, however, to give results varying among themselves, as well as less accurate than those obtained subsequently by a different process, this method was abandoned as unsuited to the requirements of the problem. III-ROTATIONS. For the measurement of the rotation of the plane of polarization the following instruments were used: (1) A pair of Nicol's prisms, one of which was stationary, and the other mounted in a graduated circle, the quartz plate being placed between the two, perpendicular to the line of collimation. The rotation was measured by the extinction of the light, or by the use of a bi-quartz or bi-selenite plate as an indicator. (2) A Laurent polarimeter, or saccharimeter, large model, having a circle 184 millimeters in diameter, graduated around the entire circumference, reading directly by a vernier to intervals of two minutes of are, and readily allowing measurements to one minute of arc. The circle was investigated for the determination of its errors, and found to be perfect within the limits of possible accuracy of reading. (3) A polaristrobometer of Wild, reading by a vernier directly to tenths of degrees, and by *Annales Sci. de l'École Normale. Deuxième série. Tom. I, p. 209. Sitzungsb. Akad. der Wissenschaften, Wien, Bd. LXXIV, p. 213. |