1908.] PUBLIC DOCUMENT — No. 33. 117 



New Standard. 



The recommendation by the Bureau of the true cubic centi- 

 meter as the basis of graduation, because it is a well-defined unit, 

 universally recognized, and for uniformity in volumetric appa- 

 ratus, appeared worthy of acceptance. The standard or basis of 

 graduation was eventually drafted as follows : — 



Section 1. The unit of graduation for all Babcock glassware shall be 

 the true cubic centimeter (0.998S77 grams of water at 4° C). 



(«) With bottles, the capacity of each per cent, on the scale shall be two 

 tenths (0.20) cubic centimeter. 



(6) With pipettes and acid measures, the delivery shall be the intent 

 of the graduation and the graduation shall be read with the bottom of the 

 meniscus in line with the mark. 



As the necessary change in graduation is slight and the 

 manufacturers few in number, there ap})ear no serious obstacles 

 in the way of the adoption of the new standard, though one 

 firm opposed it as impracticable. 



Methods of Testing, 



(«) Bahcock Bottles. — Of the several methods^ in vogue 

 for testing Babcock bottles, calil)ration with a weighed amount 

 of mercury was the most sensitive, because of the high specific 

 gravity of the metal. The process had also the advantage of 

 being generally understood and extremely simple. The figures 

 assumed for the specific gravity of mercury, hoAvever, have 

 usually been too high. According to the Bureau of Standards, ^ 

 1 cubic centimeter at 20° C. should weiojh in air asfainst brass 

 weights 13.5471 grams. The ofiicial method was readily de- 

 duced from the above. 



Section 2. The official method for testing Babcock bottles shall be 

 calibration with mercury (13.5471 grams of clean, dry mercury at 20° C, 

 carefully weighed on analytical balances, to be equal to 5 jjer cent, on the 

 scale), the bottle being previously filled to zei'o with mercury. 



1 Connecticut Agricultural Experiment Station, twenty -fiftli (1901) annual report, pp. 280, 

 281; Vermont Agricultural Experiment Station, fourteenth (1901) annual report, pp. 222, 

 223; Wisconsin Agricultural Experiment Station, ninth (1892) annual report, pp. 221, 222; 

 tenth (1893) annual report, p. 125; Testing Milk and its Products, fifteenth edition, Far- 

 rington & WoU, pp. 47-53; Modem Methods of Testing Milk and Milk Products, L. L. 

 Van Slyke, pp. 4.>-49. 



8 Correspondence. 



