EXPERIMENTS 321 



fortably warm. This excess of heat is thrown off by 

 wetting the surface of the body with perspiration. Here 

 again is another example of the conservation of energy, 

 since the heat is made to disappear as heat in doing the 

 work of changing the liquid water of the perspiration 

 into water vapor. 



EXPERIMENTS AND DEMONSTRATIONS 



Materials : Cellulose in the form of large slivers of soft pine 

 wood; wide-mouthed bottles with tin or glass covers; matches; 

 litmus paper, blue and red; saturated solution of lime water, 

 filtered or cleared by settling; test tube; 12 in. piece of glass or 

 rubber tubing, with about 1 ^- in. bore ; 12 in. piece of glass 

 tubing, y s in. opening, bent to S shape and fitted to a rubber 

 stopper; hydrochloric acid, 1 part to 10 parts of water; sheet 

 zinc; small deep tin pan with perforated tin shelf to serve as 

 pneumatic trough; soap; ammonia; soda; cream of tartar; 

 sweet and sour milk. 



1) Acid and alkaline reaction with litmus paper: 



a) Moisten both blue and red litmus paper with dilute hydro- 

 chloric acid. Acid reaction. 



b) Moisten blue and red litmus paper with lime water. Al- 

 kaline reaction. 



c) Moisten blue and red litmus paper with water. Neutral 

 reaction. 



d) Test various substances, as soap, ammonia, soda, cream 

 of tartar and sweet and sour milk with litmus paper; arrange 

 according to their reactions as acid, alkaline and neutral. 



2) Carbon dioxide manufacture: 



a) Burn cellulose in a wide-mouthed bottle by thrusting the 

 lighted slivers under its partially raised cover, keeping the 

 bottle covered as closely as possible in order to avoid the escape 

 of the gas. Continue combustion until the wood will no longer 

 burn. Remove sliver and cover bottle tightly. Note carefully 

 every change taking place and write out observations. 



