THE FATS 23 



8. To determine melting-point of a fat or fatty acid, place a small 

 quantity in a very narrow test-tube strapped on to a thermometer with an 

 india-rubber band. Place this in a water-bath which is gradually heated, 

 and note the temperature at which it melts. 



9. Emulsification. (a) Take two test-tubes and label them A and B. 

 Place water in A and soap solution in B. To each add a few drops of olive 

 oil and shake. In B an emulsion is formed, but not in A. 



(6) Shake a few drops of rancid oil with a dilute solution of potash ; an 

 emulsion is formed because the potash and free fatty acid unite to form a soap. 

 Divide this into two parts, and to one of them add a little solution of gum or 

 egg albumin ; the emulsion is much more permanent in this specimen. 

 These experiments illustrate the favourable action of soap and of a suspend- 

 ing medium like mucilage upon the formation of an emulsion. 



Fat is found in small quantities in many animal tissues. It is, 

 however, found in large quantities in three situations, viz. bone 



FIG. 5.A few cells from the margin of a fat lobule ; /. g., fat globule distending fat cell ; n, nucleus ; 

 m, membranous envelope of the cell ; cr., bunch of crystals within a fat cell ; c, capillary vessel 

 v, venule ; c. /., connective tissue cell. The fibres of the connective tissue are not represented. 



marrow, adipose tissue, and milk. The consideration of the fat in 

 milk is postponed to Lesson VI. 



The contents of the fat cells of adipose tissue are fluid during life, 

 the normal temperature of the body (37 C., or 99 R) being con- 

 siderably above the melting-point (25 C.) of the mixture of the fats 

 found there. These fats are three in number, and are called palmitin, 

 stearin, and olein. They differ from one another in chemical com- 

 position and in certain physical characters, such as melting-point 

 and solubilities. Olein melts at 5 C., palmitin at 45 C., and stearin 

 at 53-65 C. Thus, it is olein which holds the other two dissolved at 



