TRIPLE BEAM BALANCE for weighing chemicals, measuring specific and general laboratory use
THE ANALYST'S COLUMN L. T. HALLETT, Science Editor
gravity,
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1 AST month we dealt with the history -*-^ and function of the Bureau of Customs Laboratory by A. F . Parks. This month we continue with Part II, a resume of the analytical methods used.
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Analytical Methods of Bureau of Customs
auxiliary weight)
•
From the previous outline of function it may be understood t h a t customs labora tories would have need for a continuing program of developing analytical methods. At the present the analytical methods used by customs laboratories may be divided as follows: First come official methods which are developed by customs personnel either by modification of generally recog nized methods or by development of test methods peculiar to customs needs. An other category of customs methods is those which are required by law or regulation. Frequently customs chemists consider these methods to be cumbersome and per haps even inaccurate, b u t in certain case? they have become written into the law or regulation which because of its long con tinued practice has the effect of law. Such methods cannot be changed for more mod ern, precise, or accurate methods. An example of this is the method of determin ing total sugars in sirups and other prod ucts covered b y t h e Internal Revenue Act. This Act specifically refers to the methods outlined in the Customs Regula tions of 1937. While these methods are still considered to be accurate, they are time-consuming and should be replaced b y more rapid methods. The third type of analytical methods might be called special methods devised b y the chief chemist for a particular prob lem a t hand, or they m a y be old estab lished methods published by organizations such as the ASTM, AOAC, Oil Chemists' Society, and others. In this connection, customs has a peculiar problem in con nection with assessing t h e duty on coal tar dyes. For example, an imported dye which will give substantially the same re sult ivhen used in substantially the same manner as a domestic dye is valued on a different basis from one having no domestic counterpart. This requires numerous com parison tests in the customs laboratories using samples of the imported dyes against samples of domestic dyes. T h e Division of Technical Services has a standing Committee on Laboratory Meth ods. Chemists assigned to this work are selected for their special qualifications in writing laboratory methods and for their knowledge of the special requirements of the tariff act which may be applicable to various commodities. This committee de termines t h e need for customs laboratory
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VOLUME
2 7, N O .
6, J U N E
1955
11 A
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methods generally under one of three criteria: (a) Numerous samples of one kind are encountered and a conveniently written method would be economical; (b) no standard method is available; and (c) special requirements of the tariff act re quire modification of an existing method or a completely new method is needed.
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Most customs laboratory methods are tested by an interlaboratory test proce dure conducted by the methods committee where identical or specially modified samples are sent to each customs labora tory for test. These test samples are usually forwarded in triplicate to be run on different days. The results are con solidated and treated statistically to deter mine the within- and between-laboratory variation. The information gained from this interlaboratory test procedure is used in evaluating t h e precision and accuracy of the methods.
s
Customs methods in general are not published, although a few are available in Treasury Decisions, Bureau of Customs circular letters, and Customs Regulations. Most of the methods may be made avail able in limited quantities gratis to individ uals who apply to the Division of Technical Services, Bureau of Customs, Washington 25, D . C. The Bureau of Customs Sampling Guide was issued in 1938 as a confidential booklet designed for use of customs officers only. I t has since been declassified, and the material therein m a j ' be available to interested persons. There are 16 specific sampling methods contained therein, covering from 400 to 500 named items in addition to numerous items by reference to class of compounds or materials.
VOLUME
2 7, N O . 6, J U N E
1955
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The Bureau of Customs Gauging Man ual of 1941 was issued primarily to instruct customs officers in the methods for deter mining the capacity of casks, cylinders, tank cars, and large storage tanks and in cluded methods and tables for determining quantities of distilled spirits with the use of the gaging rod. I t also included methods and tables for determining the quantity of petroleum products, molasses, and oils in large tanks. Another series of unpublished articles which may be of interest is the weighing methods used on certain imported com modities. These are published in the form of bureau circular letters and may be made available in limited quantities to interested persons. Among the items covered are the so-called scientific weighing methods for raw sugar, bales of staple rayon, refined sugar, tanning extracts, tobacco, burlap, and wool. For the most part these meth ods are used exclusively by customs to "calibrate" weights furnished by the .importers or public weighers, or on in voices. Generally, weighing is performed b y selecting a minimum number of bales, bags, or individual containers and com paring the customs weight of these bags with the foreign weight on the same item. With a minimum number of comparisons, a conversion factor, correct within sta tistically controlled limits, is used to con vert a total foreign or the public weigher's weight into a customs weight, which is then used for duty purposes. By the use of these methods valuable time in unloading steamships and handling merchandise is saved, and the final weights obtained are considered as good as or better than the formerly used 100% weighing by customs.
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