306. STANDARDS FOR BABCOCK 

 GLASS WARE. 



(Adopted by the Association of Official Agricultural Chemists of 

 North America.) 



SEC. 1. The unit of graduation for all Babcock glassware 

 shall be *the true cubic centimeter (.998877 gram of water at 

 4 C.). 



(a) With bottles, the capacity of each per cent, on the scale 

 shall be two-tenths (0.20) cubic centimeter. 



(b) 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. 



SEC. 2. The official method for testing bottles shall be cali- 

 bration with mercury (13.5471 grams of clean, dry mercury at 

 20 C., carefully weighed on analytical balances, to be equal to 

 5 per cent, on the Babcock scale), the bottles being previously 

 filled to zero with mercury. 



SEC. 3. Optional methods. The mercury and cork, alcohol and 

 burette, and alcohol and brass plunger methods may be employed 

 for the rapid testing of Babcock bottles, but the accuracy of all 

 questionable bottles shall be determined by the official method. 



SEC. 4. The official method for testing pipettes and acid 

 measures shall be calibration by measuring in a burette the 

 quantity of water (at 20 C.) delivered. 



SEC. 5. The limits of error. (a) For Babcock bottles shall 

 be the smallest graduation on the scale, but in no case shall it 

 exceed five-tenths (0.50) per cent., or for skim milk bottles one- 

 hundredth (0.01) per cent. 



(b) For full-quantity pipettes, it shall not exceed one-tenth 

 (0.10) cubic centimeter, and for fractional pipettes, five-hun- 

 dredths (0.05) cubic centimeter. 



(c) For acid measures it shall not exceed two-tenths (0.20) 

 cubic centimeter. 



