68 AGRICULTURAL CHEMISTRY 



considered to be too large in amount for perfect sanitary 

 conditions. While carbon dioxid is a product of respira- 

 tion, and is of no direct economic importance to animals, 

 it is indirectly of great importance because of its serving 

 as food for plant bodies. It is a heavy gas, but in a room 

 it diffuses and is quite evenly distributed. Its presence 

 in pure and in respired air can be shown by the following 

 experiment : 



Experiment 9. Pour 10 cc. of lime water (calcium hydrate) 

 into a test-tube, and blow through it, using for the purpose a clean 

 glass tube. Observe the precipitate of calcium carbonate. Expose 

 about 10 cc. of lime water in a beaker for twenty-four hours, and 

 observe the result. The reaction which takes place between the 

 lime water and the carbon dioxid of the air is as follows : 

 Ca(OH) 2 -f C0 2 = CaCO 3 + H 2 O. 



Questions, (i) What caused the precipitate to form? (2) What 

 was produced ? (3) Is CaCO 3 soluble in water? (4) How do you 

 determine whether or not a gas is CO 2 ? (5) How does the product 

 from this experiment compare with that from the burning candle ? 



In the ventilation of dwellings, barns and stables, it is necessary 

 that the products of respiration be removed as completely as possi- 

 ble and not allowed to accumulate and endanger health. Pure air 

 is as important as pure food or water. Impure air is frequently the 

 cause of disease and indirectly it may, by lowering the vitality of 

 the individual, prepare the way for disease. When gasoline or 

 kerosene is used as fuel, more thorough ventilation is necessary 

 than when wood or coal is used, because the products of combus- 

 tion from the gasoline and kerosene are given off into the room 

 instead of being carried out through the chimney. The subject of 

 ventilation, which forms a part of sanitary chemistry, is, as a rule, 

 given too little attention. 



69. Ammonium Compounds. When nitrogenous or- 

 ganic compounds decay, ammonia gas, NH 3 , is given off. 



