FATS AND SOAPS 



157 



are volatile and soluble in water, myristic, palmitic, and stearic acids are 

 insolublejn water, and not easily volatilised ; while the acids of intermediate 

 molecular weight have intermediate properties. In fact, the boiling points 

 are found to rise, and the solubility to diminish, as the molecular weights 

 in a series increase. 



Among the properties of fats that need to be especially 

 noticed are (i) solubility in ether, (2) emulsification, and (3) 

 saponification with an alkali. Bruise any dry vegetable sub- 

 stance, e.g. straw, maize, rice meal, linseed, or bran, in a mortar, 

 and, having transferred to a test-tube, shake with ether. Pour 

 off the ethereal liquid and evaporate in a dish over the water 

 bath. The residue will consist of the fat (together with wax) 

 of the vegetable substance. 



Shake some olive oil with water ; notice that the oil quickly 

 separates from the water, and, being lighter, rises and floats 

 upon the surface. Now add a drop of solution of caustic 

 potash, and shake again. Observe that an emulsion is now 

 produced, the fat being separated into minute particles which 

 do not readily aggregate. 



When fats are decomposed by saponification with an alkali, 

 glycerine and a soap are formed. Thus : — 



C3H5.3Ci8H3,02 -f sNaOH = C3H53OH -f 3NaCi8H3,02. 



Glyceryl stearate Caustic Glycerine. Sodium stearate 



or stearin. soda. or soap. 



Boil together in an iron dish 50 grams of tallow with caustic 

 soda, in slight excess as calculated from the equation, dissolved 

 in 250 c.c. of water, until complete saponification has occurred. 

 Add strong brine to the mixture to " salt out " the soap, it being 

 insoluble in solution of common salt. Separate from the soap 

 the aqueous liquid containing the glycerine, evaporate it to 

 dryness, dissolve out the glycerine from the residue with strong 

 alcohol, and evaporate the alcoholic solution until a syrupy 

 residue of the glycerine is obtained. Note its sweet taste. 

 Dissolve a portion of the soap in water, place the solution in 



