64 ORGANIC AGRICULTURAL CHEMISTRY 



without evaporating add about 50 g. of common salt, NaCl, and stir 

 thoroughly. The addition of salt causes the soap to separate as a 

 solid layer, (b) Test the residue or the separated cake for its soapy 

 character, (c) Dissolve some of the soap in water and add sulphuric 

 acid until the solution is distinctly acid. The solid separating is the 

 free acid originally combined with the glycerol as an ester in the fat. 

 The reactions are as follows : 



CH2-OOC-C15H31 CH2-OH 



CH-OOC-C15H31 + 3 NaOH -> CH-OH + 3 CisHsi-COONa 



I I Soap 



CH2-OOC-C15H31 CH2-OH 



Glyceryl tri-palmitate Glycerol 



(fats) 



CisHai-COONa + H2SO4 -^ C15H31-COOH + NaHS04 



Soap Palmitic acid 



(2) Properties of Fats and Soap, (a) Mix 5 c.c. of oil or melted fat 

 with an equal volume of water. Shake and then allow to settle. 

 Explain, (b) Place two filter papers in two funnels. Keep one per- 

 fectly dry and moisten one with water. Pour 10 c.c. of oil or melted 

 fat upon each paper. Explain, (c) Mix 5 c.c. of oil with an equal 

 volume of soap solution. Shake and allow to stand a few minutes. 

 This mixture is called an emulsion. Filter this emulsion through a 

 wet filter paper. Explain. 



(3) Hard Water, (a) Place 10 c.c. of limewater, Ca(0H)2, in a test 

 tube. With a glass tube blow your exhaled breath through the lime- 

 water. What is the precipitate which forms? Continue to blow 

 through the solution until the precipitate first formed dissolves. 

 What compound is now present in solution? Take one-half of this 

 solution of calcium acid carbonate and boil thoroughly. Explain. 

 Filter or decant off the clear Hquid. Boil again to be sure all car- 

 bonate has been precipitated. The reactions are as follows : 



Ca(0H)2 + CO2 -> CaCOg + H2O 



Calcium carbonate (insoluble) 



CaCOa + CO2 + H2O -^ Ca(HC03)2 



Calcium acid carbonate (soluble) 



Ca(HC03)2 + heat -^ CaCOa + CO2 + H2O 



