28 THE FATS. 



a dry test-tube until they commence to decompose, and see if they 

 give the irritating odor of acrolein. If the acids were washed 

 clean and if the fat was completely saponified this should not ap- 

 pear. Try the same test on any of the fats, and the odor will be 

 given. It is best produced by adding before heating a little acid 

 potassium sulphate. 



59. Neutralize the first filtrate from the acids, which 

 contains the glycerin, by adding a little powdered chalk, 

 then evaporate the mixture to complete dryness on a water- 

 bath. Extract the glycerin from the powdered mass by 

 alcohol and evaporate this on the water-bath. If the glyc- 

 erin is to be further purified this residue should be ex- 

 tracted with absolute alcohol and the alcoholic filtrate 

 evaporated. The thick liquid is the glycerin, as is shown 

 by the taste. 



60. Mix 2 grammes of lead monoxid (litharge) with 11 cubic 

 centimeters of olive-oil and 75 cubic centimeters of water. Boil 

 until the oil is entirely converted into the lead soap. This is 

 "lead plaster." Filter it off; wash the insoluble soap with water 

 and evaporate the filtrate with the wash-water in an evaporating 

 dish on a waterbath, as long as its volume decreases. The glycer- 

 in remains. It contains lead; if the pure substance is desired 

 this can be removed by diluting with water and passing hydrogen 

 sulphid into< it. 



Glycerin dissolves many metallic oxids, e.g., precipitated, 

 washed cupric oxid dissolves to a blue liquid. Try this. A borax 

 bead when dipped in glycerin gives a green color when heated in 

 the Bunsen flame* 



61. THE PREPARATION OF PURE PALMITIC ACID. Melt in 

 hot water 10 grammes of bayberry wax which is nearly pure 

 palmitin and add 20 cubic centimeters of a 20 per cent, solution of 

 sodium hydrate. Boil it until a drop makes a soapy solution 

 when poured into a test-tube of water. Sodium palmitate has 

 been formed together with glycerin, carbon dioxid and water. 

 (Write the equation for the reaction.) Acidify slightly the soap 



