THE BUREAU OF STANDARDS 215 



arts by an experienced eye. The temperature scale of the bureau is now 

 reproducible to about 1° at 1000° C. and to about 10° at 2000° C. 



It should not be supposed that the constant efforts for higher accu- 

 racy are made to satisfy the dreams of the pure scientist; they are 

 demanded by the requirements of technical tests and commercial proc- 

 esses. The character of some products is materially affected by a varia- 

 tion of 20° in the very high temperatures employed in their manu- 

 facture, and an accuracy of about 10° is required. To meet this demand 

 there must be the exercise of man}*- precautions and the elimination of 

 many sources of error. 



The importance of great accuracy is well illustrated by a test which 

 the bureau was called on to make in a dispute between a purchaser and 

 a seller of coal, in a case where the contract was based on the heat value 

 of the coal, with a penalty clause for any deficiency in the heat value, 

 and a premium for any excess above the stipulated one. A difference of 

 about 0.05° was found between the thermometers used by the two 

 parties. While this difference was small, it was sufficient to bring the 

 parties into agreement, and to make a difference of some $25,000 a year 

 in the money paid for the coal. 



The division of optics has been engaged in many investigations of 

 moment, but none of more practical value than the improvements in 

 the application of polarized light to the testing of sugar solutions by 

 means of the polariscope. Plane polarized light differs from common 

 light in having all its vibrations reduced to a single plane. The optical 

 property of a sugar solution utilized to determine the amount of sugar 

 present is its property of rotating the plane of polarization when the 

 polarized light passes through it. The degree of rotation determines 

 the per cent, of sugar present. 



The bureau is able to make immediate application of its research 

 work in this field, thus directing public attention to the results attained. 

 As a result of the polariscopic tests of imported sugars at the bureau, 

 the differences in the findings at the five principal sugar ports of entry 

 have been reduced to 0.2 per cent. The importance of this work grows 

 out of the fact that it increases the accuracy of the tests made on duti- 

 able sugars and rigidly defines the scientific basis on which the revenues 

 from them are collected. 



The division of chemistry is in a large way auxiliary to all other 

 divisions and cooperates with them in giving such service as chemistry 

 alone can offer. It has been indispensable in the work of the division 

 of electricity; it has prepared materials in the purest form for setting up 

 Weston normal cells as standards of electromotive force, and for use in 

 the silver voltameter for the international unit of electric current. 



Much of the labor in testing supplies offered by the bidders under the 

 new system of purchase by the General Supply Committee devolves on 

 this division. The analyses of writing and printing inks, paper, and 



