_d_. Acids and alkalies have apparently little effect on this particular vitamine.
It may be well to state here however that owing to variability in behavior with variation in conditions it is dangerous to draw too general conclusions and until a given source has actually been investigated under specific cooking conditions one should not rely too strongly on analogies based on comparative experiments. This statement applies to all vitamines and presents one of the live subjects of investigation for the cooking schools and the food factories.
_e_. Little has been learned further about the chemistry of this substance. [Footnote: Since the above was put in type Steenbock has shown that the A vitamine resists saponification and that by saponifying fats which contain the A it may be possible to secure a fraction rich in the vitamine and free of fat.] Butter fat, nitrogen free and phosphorus free is shown to carry the vitamine and it is therefore assumed that the vitamine lacks these elements. It has been claimed that it may be removed from butter fat by prolonged extraction with water but this has not been confirmed by more recent experimenters. Steenbock was the first to call attention to the association of the A vitamine with yellow pigment in plant and animal sources. Butter, egg yolk, carrots, yellow corn contain it while white corn and white roots are less rich in this vitamine. This observation suggested the chemical relation between the vitamine and carotin. It has however been shown by Palmer and others that carotin is not vitamine A. This association of the pigment with the vitamine is therefore apparently a coincidence and this clue has failed as yet to throw light on the chemical nature of vitamine A.
II. THE CHEMICAL PROPERTIES OF VITAMINE "B"
When Funk first studied this substance he conducted all his evaporations in vacuo from fear that higher temperatures would prove destructive. Subsequent investigation however has shown that 100° has very little if any destructive effect if the vitamine is held in acid or neutral solution. Temperatures between 100° and 120° maintained in an autoclave at 15 pounds above normal pressure do tend to slowly destroy the factor. The extent of this destruction also varies with the character of the crude extract. In general, then, there is little fear of injuring this vitamine in ordinary cooking temperatures if the use of alkali is avoided.