70 LABORATORY EXERCISES 



your thumb or a cork, and shake it vigorously. What becomes 

 of the oil? Half fill the test tube with water, and shake it 

 again. ,Do you get a good suds? The oil and the alkali react 

 to give a soap. 



b. Dissolve 5 g. of sodium hydroxide in 35 g. of water, and 

 put the solution in a clean "tin" can. Add 2 g. of lard; then 

 carefully heat the mixture to boiling. Place a loose cover over 

 the can, and do not allow the alkali to be spattered into your 

 eyes. 



Boil the mixture for about 20 minutes; then add to it 10 

 g. of salt in 3 portions. Stir the contents of the can, but 

 do not look into it ! After the salt is all in, boil the mixture for 

 10 minutes more; then let it cool thoroughly. 'The soap should 

 separate out as a solid cake that floats upon the solution^ 

 Take it out, rinse it with water, and lay it on blotting paper or 

 newspaper to dry. 



c. Put a small piece of the soap you have made into a test 

 tube, and shake it with some water. Does it make a good 

 suds? Review Exercise 30, 6. 



Test the soap solution with red litmus paper. Is there a 

 strong alkaline reaction, or not? 



d. Shake together in a closed test tube about l / 6 of a test 

 tube full of linseed oil and half a test tube full of limewater. 

 What is the appearance of the mixture? Do the materials 

 separate easily when allowed to stand? What is an emulsion f 

 See 91, text. 



EXERCISE 68 

 TESTING OF COTTON AND WOOL 



Apparatus and Materials. Glass or porcelain dishes, 10 per cent 

 sodium hydroxide solution, white cotton cloth and thread, white 

 woolen yarn, dilute sulphuric acid, mixed cloth, burner, beaker or 

 "tin" can. 



