ON HARVESTING SOILS AND COMPOSTS. 62^ 



nourishment in that condition, or whether complete decomposition into- 

 gaseous elements must be the preparatory step to their appropriation. In 

 either case the alkalies must be eflficacious, for the solvent action which they 

 exercise advances by one degree at least their final decomposition. 



1631. " That some important function of these bodies is intimately associated 

 with then- extreme avidity for alkalies, especially for ammonia, can scarcely be 

 doubted. So great is their tendency to unite with it that it is exceedinglj' 

 difficult to procure acids of this series free from it. Not only do they absorb 

 all of this alkali they come in contact with, but it is suspected that they 

 actually, like many other jDorous bodies, promote the combination of oxygen 

 and hydrogen, and form ammonia, — a beautiful provision of nature, by which 

 the products of natural decomposition to which vegetables are disposed are 

 endowed with the property of generating that which is necessary to their own 

 solution, and consequently to their assimilation as food ; not merely of col- 

 lecting, but of generating ammonia for their own use." 



1632. In order to accomplish this, however, certain elements must be sup- 

 plied ; and all who have examined this question admit that the value of manures 

 is in proportion to the nitrogen or phosphates which they contain, more espe- 

 cially the former; for nitrogen is almost synonymous with ammonia, that being 

 the chief source of nitrogen for plants. "Let the cultivator then," saj's Dr. 

 Scoffern further on, " take care of his ammonia ; let him take care of his phos- 

 pates ; let him prevent the loss of all soluble matters from his compost-heap." ' 



1633. The first and most important source of these elements is farm-yard 

 manure, which, in its fresh state, consists of the refuse of straw, of green vege- 

 table matter, and the excreta of domestic animals. Horse-dung varies in its 

 composition according to the food of the animal, being most valuable when 

 fed upon grain, being then firm in consistence and rich in phosphates. Sheep- 

 htter is a very active manure, and rich in sulphur and nitrogen ; " for if a slip 

 of white pajDcr, previously dipped in a solution of lead, be exposed to the 

 fumes of fresh sheep-dung, the paper will be blackened : a sure test of the 

 presence of sulphur." 



1634. Cow-litter is cooler, and less rich in nitrogenous or azotized matter ; 

 but it is rich in salts of potash and soda, and thus better adapted for delicate 

 and deep-rooted plants. Swine's dung is still less azotized and more watery, 

 and full of vegetable matter,— generally seeds not dead, but ready to germi- 

 nate ; but the most important of all manures is the urine from the stables and 

 drainings of the dung-heap, which is wasted daily to an enormous extent. 

 "The urine of carnivorous animals," says the authority we have already 

 quoted, " is rich in the principles urea and uric acid. In herbivora, hip- 

 puric acid takes its place ; but in all cases it is rich in nitrogen, and, when 

 allowed to putrefj'^, ammonia is evolved. Urine is thus one of the most important 

 constituents of farmyard manure." 



1635. The composition of manure is a very heterogeneous mixture. It 

 may be broadly viewed as a mixture of humic acid bodies fixed in alkaline 

 salts, and nitrogenous bodies capable of yielding ammonia ; and it becomes an 



