FAT CRYSTALS 



moved and the supernatant ether solution carefully decanted from the crystallized 

 glycerids, which are usually found in a firm mass at the bottom of the vessel. Cold 

 ether is then added in three portions of 5 cc. each from a small wash bottle, care being 

 taken not to break up the deposit while washing and decanting the first two portions. 

 The third portion is, however, actively agitated in the cylinder with a sharp rotary 

 motion and by a quick movement transferred, with the crystals, to a small filter paper. 

 The crystals are then washed with successive small portions of the cold ether, with the 

 use of the wash bottle, until 10 to 15 cc. has been used, dependent on the amount of 

 crystals. Then by means of a slight exhaust the 

 small amount of remaining ether is rapidly re- 

 moved. The paper with its contents is then 

 transferred to a suitable place, where it should 

 be spread out and any large lumps of the glyc- 

 erids broken up by gentle pressure. When 

 dry the mass is thoroughly comminuted and the 

 melting point of the crystals determined. 



As the difference between the melting points 

 of the glycerids obtained in this manner from 

 beef fat and lard is not very great, being only 

 about 3.5 degrees, and as the writer has men- 

 tioned a standard melting-point temperature for 

 the glycerids of pure lard obtained under certain 

 conditions, a description of the apparatus used 

 in determining the melting points, together with 

 its manipulation, is essential and may be of 

 some assistance. 



Determination of the Melting Point. A 

 large test tube approximately 150 by 25 mm., 

 containing water (free from air) into which the 

 bulb of a thermometer 1 with the melting-point 

 tube attached is immersed, is placed in a beaker 



of water and so adjusted that the surface of the liquid contained in the two vessels 

 is at the same level. The water in the beaker should be heated rapidly to about 

 55 C. and that temperature maintained until the thermometer carrying the melt- 

 ing-point tube registers between 50 and 55 C., then heat is again applied and the 

 temperature of the outer bath carried somewhat rapidly to 67 C., when the lamp is 

 removed. The melting point of the crystals is regarded as that point when the 

 fused substance becomes perfectly clear and transparent. The use of a dark 

 background placed about 4 in. from the apparatus will prove of advantage. 



The melting-point tube should be of about i mm. internal diam., sealed at one 

 end and with a slight flare at the other extremity, in order that the loading may be 

 expedited. The amount of the substance taken for each determination should be 



1 The thermometer used was one graduated in one-fifth degrees and extending 

 from o to 100 C. 



FIG. 54. Beef fat crystals. 

 a, Clusters of crystals as seen 

 under the low power of the 

 compound microscope; b, crys- 

 tals highly magnified. 



