578 EVERYDAY SCIENCE 



soda as the first step in mercerizing it. Silk also dissolves in caus- 

 tic soda, but not so readily as wool. 



To Distinguish between Silk and Mercerized Cotton. Put a 

 little concentrated hydrochloric acid in a test tube and heat it 

 gently, stirring it with a chemical thermometer until the ther- 

 mometer registers 50 C. or a little less. Immerse a sample of the 

 fabric in the acid and keep it there for three or four minutes, being 

 careful to keep the acid at a fairly even temperature. If the fabric 

 is silk, the sample will be dissolved. If it is mercerized cotton, it 

 will remain intact. Concentrated hydrochloric acid will not dis- 

 solve either wool or cotton. 



To Distinguish between Cotton and Linen. The simplest test 

 to determine whether a fabric is linen or cotton is made, not with 

 an acid or an alkali, but with olive oil. . Thoroughly soak the fabric, 

 or a sample of it, in olive oil for about five minutes. Remove the 

 excess of oil by pressing the cloth between blotters. If the fabric 

 is linen, it will now be translucent. If it is cotton, it will be as 

 opaque as it was before soaking in the oil. 



A most interesting book for anyone who is interested in chem- 

 istry in everyday life is "The Amateur Chemist," A. F. Collins. 

 D. Appleton & Co. 



PROJECT XV. How to Make Soap from Waste Fats at Home, 



page 57 



Collecting enough waste fats for a batch of soap is likely to prove 

 a tedious performance. If through carelessness or impatience 

 a pupil then fails to produce soap, there is a discouraging loss of 

 time, effort, and money. It is recommended, therefore, that the 

 first batch of soap be made a community affair for the entire class ; 

 or that the class be divided into groups, each group undertaking 

 the project. 



If there is a school lunch-room or cafeteria, pupils may be able 

 to enlist the aid of the school kitchen in collecting waste fats for 

 the experiment. If not, pupils may each contribute a few ounces 

 of fat from their home kitchens and may divide the expense of 



