CELL-CONTENTS AND CELL-WALLS. 75 



Birch, and some other trees in winter) as a store of re- 

 serve food. Chemically, the fats are compounds esters 

 of higher fatty acids (oleic, stearic, etc.) with glycerine 

 (glycerol). They are quite insoluble in water, cold or 

 hot ; hardly soluble (except castor oil) in alcohol ; readily 

 soluble in ether, benzine, chloroform, etc. They can be 

 extracted from seeds by simple pressure, or by distillation 

 with their solvents, but not by distillation with water 

 (cf. ethereal oils). 



The ethereal oils differ from the fatty oils in that they 

 may be distilled (from the leaves, etc., in which they 

 occur) along with water vapour ; also in being soluble in 

 glacial acetic acid and in chloral hydrate. At 130 C. all 

 ethereal oils are driven from sections, while the fatty oils 

 remain behind. Ethereal oils are only slightly soluble in 

 water, but they impart their smell strongly to it. They 

 are easily soluble in ether, chloroform, etc. ; the spot pro- 

 duced on paper by ethereal oils soon disappears, these oils 

 being volatile ; they agree with fatty oils in being browned 

 or blackened by osmic acid, and in being stained red by 

 alkannin and blue by cyanin. 



(a) Allow drops of (1) turpentine, (2) olive oil or 

 castor oil, to fall on different parts of a sheet of white 

 paper. The turpentine (a volatile or ethereal oil) soon 

 disappears ; the olive or castor oil remains. Other ethereal 

 oils are oil of eucalyptus, clove oil, lavender oil. 



(b) Test the solubilities of (1) fatty oils, (2) ethereal 

 oils, by placing a drop of oil on a slide in each case and 

 adding the following solvents. Olive oil, and most other 

 fatty oils, are only slightly soluble in ordinary alcohol ; 

 but are soluble in methyl alcohol as well as ether, chloro- 

 form, and carbon bisulphide. Castor oil, however, is 

 readily soluble in ordinary alcohol. Ethereal oils are 

 soluble in both ordinary alcohol and in ether. In each 

 case pour a few drops of the solution on filter paper, and 

 note the grease stain left. 



(c) Place a drop of fatty oil on a slide, add a mixture 

 of ether and absolute alcohol (equal parts), which dis- 

 solves the oil. When the ether and alcohol evaporate, 



