THE CHEMISTRY OF THE SOIL. 9!* 



Bones can also be dissolved by placing them in a pit, and drenching with a 



hot solution of lye — 1 lb. of potash lye to every 4 lb. of bones. Cover with 

 earth, and stir occasionally for two or three weeks, when the mixture may 

 be turned out to dry. 



It will be seen that treatment with acid is the most rapid, and the 

 product is more satisfactory, but a little caution is required in mixing the 

 ingredients. 



MANURES CONTAINING NITROGEN. 



Nitrogenous manures fall under three heads, according as the nitrogen 

 they contain is combined with organic matter or exists in the form of 

 ammonium compounds, or of nitrates. In the two latter forms it is soluble 

 in water, and immediately available as plant-food. Most of the quick-acting 

 concentrated fertilisers contain one or other of these compounds, usually 

 sulphate of ammonia or nitrate of soda. What is known as organic 

 nitrogen is contained in animal products, refuse, and excreta, such as blood, 

 bones, hair, meat, guano, farmyard manure, etc. 



The nitrogen in these latter products is not in a state in which it can be 

 immediately utilised by the plant, but requires first to undergo fermentation 

 within the soil, resulting in the first instance in the formation of ammonium 

 •compounds before it is available as plant-food. Although the nitrogen 

 in these different substances is usually classified for the sake of convenience 

 under the one heading of " organic " nitrogen, it occurs therein in a variety 

 of combinations, some of which are more susceptible to fermentation than 

 others, and consequently more rapid in their action. The smell of ammonia 

 is soon noticeable from such products as urine and farmyard manure, which 

 ■contain a large proportion of their nitrogen in the form of urea, whereas hair, 

 wool, &c, resist decomposition for a considerable length of time. 



The following list shows the order of solubility of the most commonly 

 oecurring of these products, the most soluble standing at the head : — 



Fresh urine. Fine bone-meal. Coarse bone-meal. 



Dried blood. Oil-cake. Horn-meal. 



Dried and pounded flesh. Fish scrap. Dung. 



Guano. Dried offal. Hair and wool. 



This list is of course only intended to show the relative solubility of the 

 nitrogen in the different substances named. It is not meant to apply rigidly 

 in all cases, nor is it possible to draw any such rigid comparison, for the 

 solubility will vary according to the fineness of division of the material, to 

 ■some extent also with the nature of the soil, and with the substances with 

 which the manures in question are mixed. The list will serve its purpose 

 if it makes clear the fact that some of these nitrogenous products are 

 more soluble than others, just as we have seen that some forms of phosphoric 

 acid are more soluble than others, and that the percentage of nitrogen alone 

 is not always a sufficient indication of the value of such manure, unless the 

 source of the nitrogen is also known. 



Those products containing their nitrogen in the most inert form, such as 

 hides, horn, hair, &c, are generally utilised by the manure-makers by treat- 

 ment with sulphuric acid as in the manufacture of superphosphate. Their 

 rapidity of decomposition is greatly increased by this means, just as mineral 

 phosphates are rendered soluble by treatment with acid. They may also be 



