460 SELECTIONS FROM ADDRESSES. 



ious mineral salts, such, for example, as sulphate of iron and 

 sulphate of alumina, and forms, with the sulphuric acid, one of 

 the most valuable saline manures, the very salt which has ac- 

 quired so much celebrity for its fertilizing properties when used 

 as a steep for seeds. 



From what has just been said, it appears that science ex- 

 plains and justifies the experience of ages, which has proved 

 that it is best to mix animal and vegetable matters together in 

 forming compost manures. Knowing that urine, by decompo- 

 sition, forms carbonate of ammonia, we are prepared to under- 

 stand the necessity of mixing it in compost with peat and gyp- 

 sum, so as to retain matters that would otherwise fly away in a 

 gaseous form. 



Carbonic acid gas is composed of one atomic equivalent of 

 carbon or charcoal, and two of oxygen or vital air. It is this 

 gas which sparkles in a glass of the beverage called soda water, 

 and that which causes the foam in a bottle of beer, cider, or 

 champaigne wine. It constitutes a small portion of the general 

 atmosphere, and is exhaled in the breath of every animal, and 

 is also produced by the combustion of wood and coals. It 

 will not support animal respiration, but, on the contrary, is 

 poisonous when inhaled into the lungs. This gas is the sup- 

 porter of respiration in plants, is absorbed by their foliage, and, 

 whenever the sun shines on them, the leaves decompose the 

 carbonic acid which they have absorbed, appropriate the car- 

 bon, and throw forth pure oxygen gas, or vital air, into the at- 

 mosphere, which goes to supply the breath of life to animals. 

 So that it is true, that our respiration, in part, feeds the vege- 

 table v/orld, and that we receive back our breath in the form of 

 fruit, flowers, and fuel, and the air is restored to its healthful 

 composition through this marvellous property of living vegeta- 

 tion. Dumas, the French chemist, says, that the leaves of 

 plants absorb carbonic acid with so much avidity, that when a 

 branch of fresh foliage is placed within a glass globe, and the 

 air is blown rapidly through with a blast bellows, it loses all 

 its carbonic acid in its passage over the leaves, provided the sun 

 shines on the plant at the time. In darkness this action does 

 not take place. Hence, it is evident, that the sun's rays serve 



