114 SCIENCE OF HOME AND COMMUNITY 



Canning under pressure. Canning is also done by steam 

 pressure outfits. Pressure raises the boiling point of water. 

 Under a pressure of five pounds, the boiling point is 228 

 degrees, and under a pressure of fifteen pounds it is 250 

 degrees. When the products are heated at these high tem- 

 peratures they are sterilized in a shorter time. Under a 

 pressure of ten pounds only one half to one third as long a 

 period is required as with the hot-water outfit. In com- 

 mercial canneries these pressure outfits are used altogether. 

 Small outfits for home use can be obtained at prices ranging 

 from $15.00 up. 



Chemistry of the kitchen. The chemicals used in the 

 kitchen may be divided into three classes, acids, bases, 

 and salts. Examples of acids are vinegar and the juices of 

 fruits. An acid has a sour taste and turns blue litmus paper 

 red. A base has a soapy taste and turns red litmus blue. 

 Ammonia and baking soda are common examples. Litmus 

 paper is used to test for acids and bases. When an acid 

 and base are mixed, it is possible to reach a stage where the 

 mixture will affect neither blue nor red litmus paper. The 

 two substances are said to have neutralized each other. If 

 this solution be evaporated, a new substance will be left 

 which is called a salt. The particular kind of salt formed 

 depends on the acid and the base used. Common salt and 

 cream of tartar are examples of salts. 



LABORATORY EXERCISE 15 



Purpose. To study the action of some substances used in 

 the kitchen. 



Materials. Red and blue litmus paper, vinegar, ammonia, 

 limewater, and lemon. 



Directions, i. Pour a little vinegar into a dish. Place in 

 it a small strip of blue litmus paper. What change takes place? 

 This is the test for an acid. 



2. Pour a little ammonia into a dish. Place in it a small 



