106 



II. DIGESTION AND ABSORPTION OF FATS 



the case of most substances which form a choleic acid, a maximum point can 

 be shown on the melting point diagram. When no compound results, no 

 maximum point can be noted. The thawing point diagram is used when 

 the melting point curve shows no sharp maximum. 545 



Figures 2 and 3 illustrate how the composition of the choleic acid deriva- 

 tive can be demonstrated from the melting point curves. 



SrWie Acid 

 D«.oxycholic 0% 1 

 And 



20 10 0* 

 80 90 1 00% 



Fig. 2. Melting point and thawing point diagram of the system sebacic acid + 

 desoxycholic acid. 626 The abscissae give molecular percentages, the ordinates 

 give the melting points (upper curve) and thawing points (lower curve). The 

 melting point of the molecular compound, 4 molecules desoxycholic acid + 

 molecule sebacic acid, is higher than that of either of its constituents. 



Senise 546 has pointed out that, in carrying out the determination of the 

 "thaw" diagrams, different choleic acids are able to form an unbroken 

 series of mixed crystals with each other. Thus, it was found that choleic 

 acids composed of the following pairs of acholic components gave an un- 

 broken series of mixed crystals: stearic acid, palmitic acid; stearic acid, 

 myristic acid; stearic acid, lauric acid; arachidic acid, lauric acid; naph- 

 thalene, anthracene; naphthalene, phenanthrene ; naphthalene, acenaph- 

 thene; anthracene, phenanthrene; anthracene, acenaphthene; phenan- 

 threne, acenaphthene ; stearic acid, naphthalene; stearic acid, anthracene; 

 and stearic acid, phenanthrene. The apocholeic acids behaved in the same 

 manner, as is shown by the following pairs: naphthalene-apocholeic acid, 



646 P. Senise, Bol. faculdade filosof., cienc. e Utras, Univ. Sao Paulo, U, Qalm., No. 1, 

 35-73 (1942). 



