26 THE FATS. 



olein. The animal oils contain more olein than stearin and 

 palmitin, consequently they melt at temperatures below the 

 ordinary ones, and are liquids. Human fat contains 67 

 per cent, to 80 per cent, of olein. 



46. Try the reaction of a fresh fat, like lard or olive- 

 oil, with a piece of litmus-paper. It is neutral ; but, if the 

 fat has been standing some time and has become rancid, it 

 may be slightly acid. 



47. Try the solubility of a few drops of olive-oil in 

 a test-tube of water. It mixes when shaken violently, but 

 soon separates at the top on standing. Add now a few 

 drops of a soap solution and shake again. The liquid be- 

 comes milky and the fat does not separate. If the oil is 

 not fresh it may be necessary to add a few drops of sodium 

 carbonate to neutralize the free acid. 



48. Examine a drop of the emulsion so formed under 

 the microscope. It will be found to consist of a great 

 number of minute globules the size being smaller the more 

 thoroughly the liquid is shaken. They are kept apart by 

 the thin film of soap which covers each one. 



49. Add a small amount of hydrochloric acid and 

 shake. The soap will be decomposed and the fat will col- 

 lect at the top, as at first. 



50. Try the solubility of a fat in ether, chloroform, 

 or gasolin, avoiding carefully the vicinity of a flame. It 

 is easily soluble. 



51. Try the solubility of tallow or lard, first in cold, then in 

 warm, alcohol. It is readily soluble in the warm alcohol and sepa- 

 rates on cooling in the crystalline form. The crystals can be ex- 

 amined with the microscope. 



52. Show that the fats are non-volatile by -placing 

 a little upon paper and warming it over a flame. It does 

 not disappear. 



