136 



Power of Soils to ahsorh Manure. 



removed from solution by this operation ; and I might be par- 

 doned for making such a statement, inasmuch as the quantity 

 that escapes is really so minute that it requires the greatest atten- 

 tion to make it evident at all, and practically it is quite correct 

 to say that all the ammonia is retained. But still it is all-im- 

 portant to the other part of the question — that is to say, to the 

 explanation of the subsequent use of the ammonia by plants — to 

 ascertain whether or not these compounds are at all soluble. 

 The double silicate of alumina and ammonia, when treated with 

 distilled water, gives to it ammonia in very small quantity. It 

 has already been shown that a gallon of water dissolves from this 

 salt about 1 grain of ammonia, or 1 part in 70,000 ; and, small as 

 this solubility is, there is every reason to believe that, with the 

 large quantity of water circulating through a plant in the dura- 

 tion of its life, there would be sufficient ammonia thus intro- 

 duced to supply all the nitrogen required for its albuminous 

 constituents. But it has been found that carbonic acid water 

 dissolves ammonia from the double silicate in considerably 

 larger quantity. Thus, 1000 grains of water saturated with 

 carbonic acid digested on the double silicate dissolved out 0.0366 

 grains of ammonia; and, at the same rate, an imperial gallon 

 would dissolve 2.527 grains. As water, then, naturally always 

 contains this gas, it follows that the solubility of the ammonia 

 will, in practice, be considerably greater than that given for 

 distilled water. Again, it so happens that the double silicate is 

 still more soluble in a solution of common salt. Thus 1000 

 grains of a solution of common salt containing 1.97 per cent, 

 of salt was found to dissolve 0.33 grains of ammonia, or at the 

 rate of 23*1 grains in the gallon, which is 20 times as much as 

 with pure water. And in a second experiment, where the 

 solution of common salt was of different strength, or 0.1 per 

 cent, of salt, the quantity of ammonia dissolved was 0.047, or 

 3.32 grains to the gallon. It is probable that many other salts, 

 such as the sulphate of soda for instance, would possess the 

 same solvent power, and this influence cannot fail to be brought 

 into play, because, wherever a salt of ammonia is arrested by the 

 double silicate of soda or other compounds of the class, a corre- 

 sponding alkaline salt is formed which acts upon the newly- 

 produced ammoniacal silicate. So that either by solubility in 

 carbonic acid water, or in the various salts which are produced 

 in the soil, it is easy to see that the ammonia may be dissolved 

 in quantity sufficient for all the purposes of vegetation. In pass- 

 ing it may be well to suggest that this extra solubility of these 

 silicious compounds in carbonic acid may in part explain the 

 action of carbonaceous matters in the soil. Independently of being 

 a real food of plants, by the carbonic acid which they furnish on 



