§ 18. MELTING-POINTS OF FAT- ACIDS. 15 



a small flame, so that the temperature rises about 1° every two 

 minutes. ^ 



§ 18. Melting-Points of Fat- Acids. — The melting-points of the 

 several fractions before and after purification are noted. If in 

 the same fraction the same melting-point is observed on both 

 occasions, or if the estimations show a difference of only 0"5°, the 

 conclusion may be drawn with tolerable safety that the precipitate 

 under examination contains only one fat-acid. The observed 

 melting-point is then compared with those of the more important 

 fat-acids, and the result arrived at confirmed, if possible, by 

 ultimate analysis. 



Experiments that have hitherto been made assign to capric acid 

 a melting-point of 30 '0°; lauric, 43-6°; myristic, 53 '8°; palmitic, 

 62-0°; stearic, 69-2°; arachic, 75-7°. 



Mixtures of two of these acids in certain proportions possess, as 

 the investigations of Heintz^ have shown, a lower melting-point 

 than either of the constituents. Heintz has also noticed that the 

 mixture, on solidifying, crystallizes in a characteristic form, or 

 remains amorphous, according to the proportion in which the two 

 constituents are present. 



^ For further information about this determination see also Pohl, in Polyt. 

 Centrbl. Jg. 1855, p. 165 ; Bergmann, in Kunst und Gewerbebl. f, Bayern. 

 Jg. 1867, Januarheft; Buis, in Annalen d. Chem. und Pharm, xliv. p. 152 ; 

 Wimmel, in Annal. der Physik, xxxiii. 121 (Am. Journ. Pharm, xli. 22, 430) ; 

 Redwood, in Pharm. Journ. and Trans. [3], vi. 1009 (1876). 



^ Annal der Physik, xcii. p. 588 (Pharm. Journ. and Trans. [1], xv. 425) ; 

 cf. ibid. Ixxxiv. 226. 



* For particulars of the examination of a fat in which stearic, palmitic, and 

 myristic acids were found, see Greenish in Pharm. Journ. and Trans. [3], x. 909. 



