FERTILIZERS. 273 



requires a resort to this method of increasing the manures, the period can not certainly be far 

 distant when it will be regarded in its true light. 



The rapidity with which farm-yard manure loses its weight is worthy of attention. It is 

 found that while the water evaporates and rises upward, it carries with it what had existed as 

 solid aliment. Obtaining the weight of ten hundred pounds of dry fodder, consisting of straw, 

 hay, etc. it is found that it will produce from twenty-three to twenty-five hundred weight of 

 manure. This, on exposure in the ordinary way, in yards, will be reduced in weight, 



In six weeks, to 21 cwt. 



After eight weeks, to 20 " 



When half rotten, to 15 " 



And finally, when perfectly rotten, to 10 " 



One half, therefore, is found to have escaped into the atmosphere. The increase in weight 

 by the process of digestion, is derived mainly from the water drank by the animal. The water 

 which has been thus absorbed, dries out rapidly ; some of it flows outwards by the pressure of 

 the mass. If nothing but water passed off in the drying process, some gain would be obtained, 

 as its bulk and weight would be diminished, and its transportation thereby facilitated. The de- 

 composition itself is necessary ; but the great desideratum is to effect these changes in the soil, 

 where the volatile parts being disengaged, they will be obliged to pass through the earth, which 

 being a good absorbent, detains them for the use of growing plants. The process of decay 

 goes on slowly, as the temperature is less, and only a small quantity of those matters can ac- 

 cumulate in one place. This is the more favorable as more time is given for the perfect absorp- 

 tion by the soil. That the soil is an excellent absorber of volatile substances is proved by many 

 direct experiments in the laboratory. It is, however, a fact familiar to most persons, and the 

 practice of covering with earth a garment which has become attainted with an execrable odor, 

 as that of the skunk, is well known in the country, and frequently resorted to, to purify them 

 from the result of such accidents. This property of the mixed earths, is one of the most im- 

 portant, without which a very large proportion of the most valuable fertilizers would pass 

 away, without benefit to the vegetation. The retention of water, too, is another property, 

 without which plants would be unable to reach maturity, and ripen their seeds. 



13. Of Composts. 



To meet the wants of plants, compound fertilizers have been manufactured, ^hich are de- 

 signed to contain all the elements which they require during their stages of development. 

 These artificial compositions must be based on a knowledge of all their leading constituents, 

 and really of the relative proportions which are found in them. With this knowledge, it is 

 possible to put together those substances which may be required for any crop. 



The true way to form a compost is to select the base of the composition, which should be 

 the most important matter in the constitution of the vegetable : this substance should be phos- 

 phate of lime. To this may be added those salts which contain the alkalies, sulphur, carbon 

 [AcRictTLTirRAi. Refort — VoL. lu.] 35 



