116 EXPERIMENT STATION. [Jan. 



13.5463 at 20° C). The Wagner Glass Works reported 1 

 cubic centimeter as equal to 13.59 grams of mercury at 60° F., 

 which was probably the Molir cubic centimeter. 



The differences were not large or the errors especially serious, 

 but the need of a scientific standard was unmistakable, if uni- 

 formity was to be secured with a safe interchange of apparatus. 

 Only the limit of error has permitted the interchange of appa- 

 ratus in the past, which is a point to be noted. 



Reasons for a New Standard. 

 With these facts at hand, it was necessary to submit the case 

 to some recognized authority for a decision, or at least advice 

 as to what action ought to be taken. This plan also seemed the 

 most promising for the reason that the two parties interested, 

 the manufacturers 1 and the State officials, 2 neither agreed with 

 each other nor among themselves as to a standard or methods 

 of testing. The matter was finally referred to the National 

 Bureau of Standards at Washington, as the body best fitted to 

 deal with the case. Director Stratton 3 wrote as follows : — 



We are decidedly of the opinion that there would be less likelihood of 

 errors in milk-testing work if all volumes were expressed in true cubic 

 centimeters. It of course does not make any difference what unit is used, 

 provided the same one is used to measure the milk sample and the fat; 

 but if — as might easily happen — the pipettes used to measure the milk 

 are graduated on one basis and the neck of the Hash on another basis, 

 serious errors might be introduced in the result. 



Referring again to the question of graduating Babcock ware for testing 

 milk, which we have given some attention, we hope that you will see your 

 way clear to adopt as the unit in this work the true cubic centimeter at 

 20° C. This, we feel confident, will }>revent confusion in the end, by 

 bringing the apparatus used in testing milk and other dairy products in 

 agreement with the volumetric apparatus used by chemists in general. 

 While the practice of using the gram of water at a certain temperature 

 may have possessed some advantages in Mohr's days, we doubt very much 

 whether it woidd be any convenience to use such units as the gram of 

 water at L5°, L7.5° or '20° at the present time. 



The use of the true cubic centimeter is necessary in all absolute work, 

 and it cannot under any circumstances be dispensed with. 



i Loco citato. - Station reports and correspondence. 3 Correspondence. 



