VITAMIN A AND CAROTENE 253 



where E — optical density for 1 cm. cuvette = 2 — log per cent 

 transmission with 1 cm. cuvette. The factor 637 is based on an E 

 (1%, 1 cm.) of 1720 for vitamin A palmitate in alcohol at 328 m/x, 

 calculated as free alcohol. The factor 480 is based on an E (1%, 

 1 cm.) of 2080 for /3-carotene (Sniaco) in kerosene-xylol. 



