tory under regular serial numbers, the identifying marks having been removed, after having been first entered in a special record, together with their respective serial numbers. Samples at the port of importation and those sent for exchange shall be tested in all respects as provided in articles 752 to 756, inclusive, and the separate tests of such samples, together with the accepted tests, shall be promptly reported every second day from each port to the Director of the Bureau of Standards, customs Form 6473, under their respective identifying marks. Complete record of all exchange tests shall be kept on customs Form 6481.

Art. 732. Exchange tests for dry substance.-On each alternate day, beginning with Tuesday, a sample of sugar will be tested in the dry substance at each of the ports named in article 730 and duplicate samples of the same sugar shall at the same time be exchanged, as directed in article 730. The duplicates shall be prepared, marked for identification, and forwarded in manner as provided in article 730. Such samples shall be sent to the laboratory as soon as received, under their respective identifying marks, and reports of tests shall be promptly forwarded every second day from each port to the Director of the Bureau of Standards under such marks. Such reports shall show the direct polarization, the percentage of moisture, and the test in the dry substance. When sugars are imported and tested at any port other than those named in article 730, samples shall be tested in the dry substance at the port of importation and duplicate samples shall be transmitted for like test to the Bureau of Standards. The samples shall be prepared and reports of said tests shall be made in all respects as herein prescribed for samples exchanged and tested at the said first-named ports. Reports of tests prescribed in this and the preceding paragraph shall be made on customs Form 6473. All requests by the Director of the Bureau of Standards for retests of duplicate exchange samples, Form 558, Department of Commerce, of either the polarization or the dry substance at the ports mentioned in articles 730, 733, and 734 shall be immediately complied with and the retest completed not later than the close of the first official day after the receipt of such request, and the results forwarded on customs Form 6473. When for any reason the retests requested by the Director of the Bureau of Standards are

not completed by the close of the first official day after the receipt of the request, the retests shall not be made and the appraiser shall furnish the Director of the Bureau of Standards with a detailed statement why said retests were not made as herein provided.

Art. 733. Exchange samples for Baltimore, Savannah, and San Francisco. The provisions of articles 730, 731, and 732 shall also be in force with respect to a similar series of exchange samples between the ports of New York, Philadelphia, Baltimore, and Savannah, and the Bureau of Standards. The appraiser at San Francisco shall forward once each week an exchange sample to the Bureau of Standards in accordance with the provisions of article 732.

Art. 734. Molasses and sirup exchange samples.(a) In order that the results of the testing of imported molasses at the several ports may be compared, it is directed that the appraisers at the ports of New York, Boston, Philadelphia, Baltimore, and New Orleans shall test one sample of molasses each month and send a duplicate one-half liter sample, properly numbered and labeled, to the Bureau of Standards. The sample shall be mailed in a screw-top metal container. The results of tests shall be promptly forwarded to the Director of the Bureau of Standards and shall show separately the sucrose (Clerget), the reducing sugars, and the total sugars.

(b) A reserve portion of each sample consisting of not less than one-half liter shall be retained by the examiner for retest purposes. All requests by the Director of the Bureau of Standards for retests of duplicate samples shall be immediately complied with.

Art. 735. Adulterated refined sugars.-Samples of all refined sugars shall be sent to the laboratory to determine whether the same, after having been refined, were tinctured, colored, or in any way adulterated. At ports where the Government has no facilities for making such expert examination, samples of all refined sugars shall be forwarded to the Bureau of Standards and the appraiser at the nearest of the following ports: New York, Boston, Philadelphia, New Orleans, Baltimore, Savannah, and San Francisco. Said appraiser will cause the necessary expert examination to be made and report thereon to the collector of the port of importation.

Art. 736. Preservation of sugar samples.-All samples of sugar sent to the laboratory for test must be preserved as nearly as possible in the same condition as when received, and shall be returned therefrom to the examining room in such condition. 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 marks, securely sealed air-tight, and held in safe custody in the examining room 30 days from the date of test for such further test or investigation as may be ordered by the Director of the Bureau of Standards. In case any exchange samples have 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 Director of the Bureau of Standards.

Art. 737. Care of apparatus.-All screens used in the mixing of samples, sample buckets, sample cans, reserve jars, etc., when once used, shall be thoroughly washed, dried, and allowed to cool before being used a second time.

Art. 738. Admission to examining rooms.-All persons shall be denied admission 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.

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LABORATORY PROCEDURE

Art. 739. Interpretation of "testing by the polariscope." The expression "testing by the polariscope * sugar degrees," occurring in a tariff act, shall be construed to mean the percentage of sucrose contained in the sugar shown by direct polarimetric estimation.

Art. 740. Laboratory records.-A permanent record of all samples received from the examiner shall be kept in the laboratory. The samples shall be identified therein by their serial numbers arranged in the order in which they are received. It shall be the duty of the chemist in charge to report the results of all tests of such samples made and recorded, severally, including the third and fourth tests, when made, to the assistant appraiser or examiner in charge of classifications.

Art. 741. Arrangement of laboratories.-Plans for laboratories for the testing of sugar and molasses must be

approved by the Commissioner of Customs. 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 heat, so that the temperature may be controlled, and shall not be too near any source of heat which can not be controlled. The polariscopes shall be placed in the darkest portion of the room whenever possible, and the top of the table upon which they are placed shall be surrounded on three sides by blackened partitions or walls not less than 3 feet in height. If necessary, suitable curtains may be hung around the polariscope to exclude extraneous light. The surroundings of the polariscope shall be such as always to permit the air from the remainder of the room to circulate around the instruments with the greatest freedom. The separation of the lamp from the instruments will be accomplished by the wall around the top of the table. The opening in the partition between the lamp and the instrument shall be as small as possible and yet allow sufficient light for the proper illumination of the polariscope. The polariscope shall not be near ovens, assay furnaces, hot-water heaters, or any other source of heat.

Art. 742. Standardized apparatus.-All thermometers, flasks, weights, polariscope tubes, polariscope tube cover glasses, quartz control plates, and polariscopes, used in the work of testing sugar, shall be standardized at the Bureau of Standards, Department of Commerce, and, with the exception of the polariscope tube cover glasses and weights, shall be marked with the initials "U. S. C. S.," and bear the stamp of the Bureau of Standards. No test of sugar shall be made with apparatus which is not properly marked unless special authority is given by the Secretary of the Treasury.

Art. 743. Standardization temperature.-All the apparatus used in the work of testing sugar by the polariscope shall be standardized at a temperature of 20° C.

Art. 744. Thermometers.-All thermometers shall have the centigrade scale and be graduated to one-fifth of a degree or less.

Art. 745. Sugar flasks.-(a) The flasks shall have a height of 130 millimeters; the neck shall be 70 millimeters in length and have an internal diameter of not less than 11.5 millimeters and not more than 12.5 millimeters. The upper end of the neck shall be flared, and the gradu

ation marks shall be not less than 30 millimeters from the upper end and 15 millimeters from the lower end of the neck.

(b) All flasks shall be standardized to contain 100 metric cubic centimeters at 20° C. The glass funnels used in filtering shall have a diameter of approximately 90 millimeters. The cylinders shall have a height of approximately 125 millimeters and a diameter of approximately 40 millimeters.

Art. 746. Laboratory weights.-Only brass weights shall be used, and they shall be forwarded to the Bureau of Standards for standardizing not less than once a year. A sufficient number of standardized duplicate weights shall be kept in reserve in each laboratory to take the place of those being standardized.

Art. 747. Polariscope tubes.-The length of all polariscope tubes shall be either 100 millimeters ±0.03 millimeter or 200 millimeters ±0.03 millimeter, and the diameter of the opening through the tube shall be not less than 9 millimeters. No tube shall be retained in use that has become bent or dented or has had its threads injured sufficiently to make the adjustment of the cap difficult.

Art. 748. Quartz control plates. All quartz control plates shall be mounted in a brass retaining box which shall exert no pressure whatever upon the plate and yet allow it minimum play. Each plate will be accompanied by a table, signed by the Director of the Bureau of Standards, giving its exact value at different temperatures from 10° to 35° C.

Art. 749. Standard sugar solution.-All polariscopes shall be so standardized that when a 200-millimeter tube filled with the standard sugar solution is polarized at 20° C. the instrument shall read 100° S±0.01° S. All points on the scale shall indicate percentages of the standard solution. The standard sugar solution shall be prepared by dissolving 26 grams of pure sugar in pure water and making up the volume to 100 metric cubic centimeters, all weighings to be made in air with brass weights and the volume to be completed at 20° C. A length of 200 millimeters of the standard sugar solution shall be considered to give a rotation of 40.763°, for light of wave length 5,461 centimeters X 10-8.

Art. 750. Polariscopes and their adjustment.-(a) All polariscopes used in the testing of imported sugars shall