420 GLOSSARY 



Consumption of a gas, to burn it in order to make heat or light, or to 

 use it for making compounds. Green plants consume carbon dioxide 

 gas of the air when they make starch. Animals consume oxygen 

 when they breathe. 



Con tam'i nate, to infect with poisons, filth, or with disease germs. 

 Surface water from a house or barn flowing into a well by a short 

 passage may contaminate the water and render it unfit for use. 



De com pose', to separate into simpler substances or parts. To de- 

 compose water is to separate it into hydrogen and oxygen. Plants 

 decompose when they decay. 



Den'si ty of a substance is the ratio of its weight in grams to its volume 

 in cubic centimeters. One cubic centimeter of water weighs one 

 gram, hence its density is one. 



Di'a phragm, a large thin muscle which forms a partition between the 

 lungs and digestive organs of the human body and assists in breath- 

 ing. It is arched upward, and when it contracts the chest cavity is 

 enlarged and air rushes in to fill the lungs. 



Di'a stase, a ferment found in cereal grains. It changes starch to sugar 

 when the temperature is right and sufficient moisture is present. 

 When conditions are favorable for plants to grow, diastase can act. 



Digestive fluid, a fluid which contains ferments that make food soluble 

 in water. Examples. Saliva in the mouth, gastric juice in the 

 stomach. 



Di lute', to make less strong or less concentrated. Vinegar, ammonia, 

 and alcohol may be diluted by adding water. 



Dis so lu'tion, the process of dissolving a crystallized substance in a 

 liquid. Sugar and salt can be dissolved in water. Heat is often 

 required to dissolve a substance. 



Dis til la'tion, the process of separating a substance which vaporizes 

 easily from one or more substances which vaporize less easily. The 

 vapor, caused by adding heat, is liquified or condensed while passing 

 through pipes which are kept cool by water flowing over them. 



Elec tro mo'tive force (abbr. E.M.F.), the force which drives an electric 

 current. It is the difference in potential or electrical pressure at two 

 points on an electric circuit. The volt is the unit of electromotive 

 force. 



En vi'ron ment consists of the things and conditions around you which 

 may affect your life. It consists of weather, climate, plant life, ani- 

 mal life, and the social conditions made by man. Students in high 

 school adjust themselves to the conditions made by themselves and 

 their teachers, and to the changes in the weather. 



En'zyme (en'zim), a general name for a number of chemical, digestive 

 ferments, such as diastase found in cereals, pepsin and rennin fcund 

 in the gastric juice of the stomach, and ptyalin in the saliva. 



Ex'cre to ry organs are organs which take poisons and useless matter 

 from the body. Examples are the kidneys, liver, lungs, etc. 



Fehling's solution. (Named after Hermann Fehling (1812-1885), a 

 German chemist.) It is made by dissolving one part by weight of 



