arising under the provision of law referred to in the preceding paragraph, representative samples of such sugars shall be preserved in manner as provided in paragraph 33, and such samples shall be held for use until the final liquidation of the entry.

50. All samples of sugar sent to the laboratory for test must be pre served as nearly as possible in the same condition as when received, and shall be returned therefrom to the examining room in such condition with the reports of the tests. All samples tested for exchange, and all exchange samples, as soon as they have been returned from the laboratory, shall be labeled with their identifying mark, securely sealed air-tight, and held in safe custody in the examining room thirty days from the date of test, for such further test or investigation as may be ordered by the Department. In case any exchange sample has been received at any port not properly filled and sealed as herein prescribed, the appraiser at the port of receipt shall immediately notify the appraiser at the port of transmittal, and shall also report the facts to the Department.

51. Attention is hereby particularly called to the provision of article 840, Customs Regulations of 1892, prohibiting the admission of all persons to the examining rooms of the appraiser's office, except officers and employees whose duties require them to have access thereto. This provision must be strictly enforced.

52. All requests for the retesting of any mark or marks of sugar shall be properly filed, and a record thereof shall be kept by the examiner in charge of classifications.

53. These regulations shall take the place of all orders or regulations heretofore issued with reference to the sampling and classification of imported sugars and molasses.

54. The following is the form of statement which will be used as provided in paragraph 43, blanks for which will be furnished by the Department on requisition.

Daily statement of classification of sugar, etc.

Name of importer.

U. S. APPRAISER'S OFFICE,

189-.

Remarks.

STANDARDIZATION AND ADJUSTMENT OF APPARATUS AND

INSTRUMENTS.

55. All polariscopes, weights, flasks, polariscope tubes, and quartz control plates used in the work of testing sugar by the polariscope will be standardized and their accuracy attested by the Office of Standard Weights and Measures, United States Coast and Geodetic Survey. They will be marked with the initials U. S. C. R., and no test of sugar will be made with apparatus which is not so marked, unless special authority is given. Each quartz control plate will be accompanied by a table giving its sugar value at temperatures of each degree centigrade from 10° to 35°, in terms of the Ventzke scale.

PROPER ARRANGEMENT OF LABORATORIES.

56. Plans for laboratories for the testing of sugar must be approved by the Secretary of the Treasury.

The room used for the purpose shall be one that is as far removed as possible from the vibration of machinery; it must be well lighted and have some means of artificial heating, so that the temperature may be controlled, and shall not be too near steam boilers, furnaces, flues, or any source of heat which can not be controlled. The polariscope shall be placed in the darkest part of the room, and this part of the room may be darkened, if desired, by curtains or hangings. In no case, however, shall the polariscope be entirely separated from the room in which the rest of the work is performed, as the solutions must be made up and polarized at the same temperature. The lamp used for the illumination of the polariscope, on the other hand, must be separated from the instrument, as its heat tends to increase the temperature of the room and cause it to vary from time to time. The separation of the lamp from the instrument will be best accomplished by means of a board partition, making a separate compartment for the lamp, which may have its own window or opening for ventilation. The partition must be perforated with an opening just large enough for the passage of light to the instrument. If a separate compartment for the lamp can not be made, a wooden screen may be used, perforated in a proper manner, and placed on the table between the instrument and the lamp.

The table upon which the polariscope stands must be level, and the instrument itself must not be near any source of uncontrolled heat, and must not be exposed to the direct rays of the sun.

INSTRUCTIONS RELATIVE TO THE USE OF THE POLARISCOPE.

DEFINITION OF THE WORD "DEGREE" AS IT OCCURS IN THE ACT.

57. The expression "testing * degrees by the polariscope," occurring in the act, is construed to mean the percentage of pure sucrose contained in the sugar, as ascertained by polarimetric estimation. Until further notice the degree of the "Ventzke scale," as hereinafter

defined, will be considered as indicating the correct percentage of sucrose, in the form of instrument used by this Department in testing sugar. The Ventzke scale is hereby defined to be such that one degree of the scale is the one-hundredth part of the rotation produced in the plane of polarization of white light in a column 200 millimeters long by a standard solution of chemically pure sucrose at 17.50 C., the standard solution of sucrose in distilled water being such as to contain, at 17.5° C. in 100 cubic centimeters, 26.048 grams of sucrose. The density of this solution will be 1.10 at the given temperature.

In this definition the weights and volumes are to be considered as absolute, all weighings being referred to a vacuum.

DIRECTIONS FOR THE POLARIZATION OF SUGAR.

58. The following directions for the use of the polariscope in testing sugar are based upon the recommendations in a report made by a commission consisting of the chief chemist of the Department of Agriculture, the chemist of Internal Revenue, and the assistant in charge of the Office of Standard Weights and Measures, Coast and Geodetic Survey, and must, be closely adhered to in all tests of sugar for classification.

Description of instrument and manner of using.

The instrument to be employed in the testing of imported sugars for the assessment of duty is known as the half shadow apparatus of Schmidt & Haensch. It is shown in the following cut:

The tube N contains the illuminating system of lenses and is placed next to the lamp; the polarizing prism is at O, and the analyzing prism at H. The quartz wedge compensating system is contained in the portions of the tube marked F, E, G, and is controlled by the milled head M. The tube J carries a small telescope, through which the field of the instrument is viewed, and just above is the reading tube K, which is provided with a mirror and magnifying lens for reading the scale.

The tube containing the sugar solution is shown in position in the trough between the two ends of the instrument. In using the instrument the lamp is placed at a distance of at least 200 millimeters from the polarizing end; the observer seats himself at the opposite end in such a manner as to bring his eye in line with the tube J. The telescope is moved in or out until the proper focus is secured to give a clearly defined image, when the field of the instrument will appear as a round, luminous disk, divided into halves by a vertical line passing through its center, and darker on one-half of the disk than on the other, when the compensating quartz wedge is displaced from the neutral position. If the observer, still looking through the telescope, will now grasp the milled head M and rotate it first one way and then the other, he will find that the appearance of the field changes, and at a certain point the dark half becomes light and the light half dark. By rotating the milled head delicately backward and forward over this point he will be able to find the exact position of the quartz wedge operated by it, in which the field is neutral, or of the same intensity of light on both halves.

With the milled head set at the point which gives the appearance of the middle disk as shown above, the eye of the observer is raised to the reading tube K, which is adjusted to secure a plain reading of the divisions and the position of the scale is noted. It will be seen that the scale proper is attached to the quartz wedge, which is moved by the milled head; and attached to the other quartz wedge is a small scale called a vernier, which is fixed, and which serves for the exact determination of the position of the movable scale with reference to it. On each side of the zero line of the vernier a space corresponding to nine divisions of the movable scale is divided into ten equal parts. By this device the fractional part of a degree indicated by the posi tion of the zero line is ascertained in tenths; it is only necessary to count from zero, until a line is found which makes a continuous line with one on the movable scale.

With the neutral field, as indicated above, the zero of the movable scale should correspond closely with the zero of the vernier, unless the zero point is out of adjustment.

59. If the observer desires to secure an exact adjustment of the zero of the scale, or in any case if the latter deviates more than one-half of a degree, the zero lines are made to coincide by moving the milled head and securing a neutral field at this point by means of the small key which comes with the instrument, and which fits a small nipple on the left hand side of F, the fixed quartz wedge of the compensating system. This nipple must not be confounded with a similar nipple on the right-hand side of the analyzing prism H, which it fits as well, but which must never be touched, as the adjustment of the instrument would be seriously disturbed by moving it. With the key on the proper

nipple it is turned one way or the other until the field is neutral. Unless the deviation of the zero be greater than 0.5° it will not be necessary to use the key, but only to note the amount of the deviation, and for this purpose the observer must not be content with a single setting, but must perform the operation five or six times and take the mean of these different readings. If one or more of the readings show a deviation of more than 0.2° from the general average, they should be rejected as incorrect. Between each observation the eye should be allowed a moment of rest.

The "setting" of the zero having been performed as above, the determination of the accurate adjustment of the instrument by means of the "control" quartz plates is proceeded with. One or more such plates will be furnished with each polariscope, and as their sugar values vary with changes of temperature, each plate will be accompanied by a table giving its exact value at different temperatures from 10° to 35° C.

60. The plate is placed in the instrument and the field observed; it will be seen that the uniform appearance of the field is changed. The milled head is turned to the right until the exact point of neutrality is reestablished, just as described above in setting the zero. The scale is read, the observation repeated, the reading taken again, and so on until five or six readings have been made. The average is taken, readings being rejected which show a divergence of more than 0.2, and the result corrected for the deviation of the zero point, if any was found, the deviation being added if it was to the left and subtracted if to the right. If the adjustment of the instrument be correct, the result should be the value of the control plate used, as ascertained from the table, for the temperature of 20° C. A variation of 0.2 from the established values may be allowed for errors of observation, temperature, etc., but in the hands of a careful observer a deviation greater than this, after a careful setting of the zero, shows that the instrument is not accurately adjusted

After the adjustment of the instrument the setting of the zero point is dispensed with, the indication of the scale for sugar solutions being corrected by the amount of deviation shown in the reading of the control plate from its established value as ascertained from the table, at the temperature of the room.

For example: A sugar solution polarizes 80.5; the control plate just before had given a polarization of 91.4, the temperature of the room during both observations being 25° C. According to the table the value of the control plate at 25° C. is 91.7; the reading is therefore 0.3 too low, and 0.3 is added to the reading of the sugar solution, making the corrected result 80.8. The temperature of the room must be ascertained from a standardized thermometer placed close to the instrument and in such a position as to be subject to the same conditions.

The use of the new apparatus of Schmidt & Haensch, known as the triple-shadow polariscope, is also permitted and recommended.

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