228 ANIMAL FATS AND PHOSPHATIDES. 



the solid varieties of tallow but also in the vegetable fats. Stearic acid, 

 CigHseC^, is found in the free state in decomposed pus, in the expectora- 

 tions in gangrene of the lungs, and in cheesy tuberculous masses. It 

 occurs as lime soap in excrement and adipocere, and in this last 

 product also as an ammonium, soap. It also exists as alkali soap in the 

 blood, bile, transudations and pus, and in the urine to a slight extent. 



Stearin is the hardest and most insoluble of the three ordinary neutral 

 fats. It is nearly insoluble in cold alcohol, and soluble with great dif- 

 ficulty in cold ether (225 parts). It separates from warm alcohol on 

 cooling as rectangular, less frequently as rhombic plates. The opinions 

 regarding the melting-point are somewhat varied. Pure stearin, 

 according to HEINTZ/ melts transitorily at 55 and permanently at 71.5. 

 The stearin from the fatty tissues (not pure) melts at 63 C. 

 CH 3 



Stearic acid, (CH 2 )i6, crystallizes (on cooling from boiling alcohol) in 



COOH 



large, shining, long rhombic scales or plates. It is less soluble than the 

 other fatty acids and melts at 69.2 C. Its barium salt contains 19.49 

 per cent barium, and its silver salt contains 27.59 per cent silver. 



CH 2 .O.C 16 H 31 



Palmitin, or tripalmitin, C 5 iH 98 O 6 , = CH.O.C 16 H 31 O. Of the two solid 



varieties of fats, palmitin is the one which occurs in predominant quan- 

 tities in human fat (LANGER 2 ) . Palmitin is present in all animal fats 

 and in several kinds of vegetable fat. A mixture of stearin and palmitin 

 was formerly called MARGARIN. As to the occurrence of palmitic acid, 

 Ci6H 3 2O2, about the same remarks apply as to stearic acid. The mixture 

 of these two acids has been called margaric acid, and this mixture occurs 

 often as very long, thin, crystalline plates in old pus, in expectora- 

 tions from gangrene of the lungs, etc. 



Palmitin crystallizes, on cooling from a warm saturated solution in 

 ether or alcohol, in starry rosettes of fine needles. The mixture of pal- 

 mitin and stearin, called margarin, crystallizes, on cooling from a solu- 

 tion, as balls or round masses which consist of short or long, thin plates 

 or needles which often appear like blades of grass. Palmitic, like stearin, 

 has a variable melting- and solidify ing-point, depending upon the way it 

 has been previously treated. The melting-point is often given as 62 C., 

 but some investigators 3 claim that it melt? at 50.5 C. ; solidifies on 

 further heating, and melts again at 66.5 C. 



1 Annal. d. Chem. u. Pharm., 92. 



2 Monatshefte f. Chem., 2; see also Jaeckle, Zeitschr. f. physiol. Chem., 36. 



3 R. Benedikt, Analyse der Fette, 3. Aufl, 1897, p. 44. 



