analyzing the butter samples in this survey, and the results given 

 in International Units have been corrected for such loss except 

 where otherwise noted. Results given in micrograms of vitamin A 

 in this report have not been corrected. 



The carotene content of the butter was determined by washing 

 the carotene solution in Skellysolve B with either 92-percent 

 methyl alcohol or 94-percent diacetone alcohol to separate the 

 carotene from the other pigments in the butter, and then reading 

 the carotene fraction either with a colorimeter or a spectropho- 

 tometer. 



The above methods gave the results in micrograms of vitamin 

 A and micrograms of carotene. In calculating the total vitamin A 

 potency of the butter, 0.6 microgram of the carotene and 0.25 

 microgram of the vitamin A were each taken as equal to 1 Inter- 

 national Unit of vitamin A. 



Method of Obtaining Butter Samples for Analysis. — Most of 

 the States that participated in the survey divided their butter- 

 producing sections into areas in which butter was produced under 

 more or less uniform conditions and collected samples of butter 

 at weekly or monthly intervals from representative creameries in 

 each production area. The number of samples collected depended 

 on the capacity of the State experiment station to do the necessary 

 analytical work. Fortunately some of the largest butter-producing 

 States cooperated in the survey, and the extent of the sampling in 

 these States leaves little doubt about the vitamin A potency of the 

 butter they produce. Approximately 3,500 samples of butter have 

 been analyzed by the 20 State stations that took part in this study. 



VITAMIN A POTENCY OF CREAMERY BUTTER BY REGIONS 



It will be noted in table 1 that the 3 regions 

 represented in the survey produce more than 

 97 percent of the Nation's total output of 

 creamery butter, and that the 14 States in 

 which the samples were collected for analysis 

 produce about 64 percent of the total output. 

 It therefore seems reasonable to consider the 

 results obtained in these 14 States as representative of practically 

 all the creamery butter produced in the country as a whole. In 

 fact, the 12 North Central States alone produce more than 77 

 percent of all the butter made in this country, and the 6 North 

 Central States that participated in this phase of the survey pro- 

 duce more than 54 percent of the total. The results obtained in 

 these 6 States undoubtedly represent closely the potency of the 



