BULLETIN OF THE BUSSEY INSTITUTION. 369 
this sense, and it is not unlikely that some of the less insoluble 
. hydrous silicates may serve the purpose well. It is not wholly 
impossible that the absence of such things from some soils may be 
one reason why chloride of potassium is thought to be a capricious 
manure. It is possible moreover that this matter of acidity may 
furnish the true explanation of the capricious and uncertain action 
of nitrate of ammonia,* when used as a source of plant-food in 
experiments made by way of sand-culture. As is well known, 
nitrate of ammonia readily parts with some of its ammonia and ac- 
quires an acid reaction. I have noticed recently that Davy,t in 
his time, was surprised to find that solutions of nitrate of ammonia 
did not answer so good a purpose for watering plants as solutions 
of the carbonate and the chloride. He says: ‘‘ The plants watered 
with solution of nitrate of ammonia did not grow better than those 
watered with rain-water. The solution reddened litmus-paper, and 
probably the free acid exerted a prejudicial effect and interfered 
with the result.” 
Mayer has argued with considerable force that even for farm- 
practice those salts of the strong mineral acids from which plants 
assimilate the basic constituent more rapidly than they assimilate 
the acid are in general less useful manures than salts of weaker 
acids, or than those from which the plants can take either the acid 
or the base indifferently. He has even propounded the hypothesis ¢ 
that, inasmuch as the proportion which subsists between bases and 
acids in the ash-ingredients of plants are very different from the 
proportions between base and acid which obtain in the Stassfurt 
salts (7. e. in the chloride and the sulphate of potash), these sub- 
stances are of comparatively small use as manures because of the 
difficulties which plants must necessarily encounter in trying to 
assimilate food from them. It may here be said that the marked 
inferiority as a fertilizer of chloride of ammonium to the other 
ammonia-salts, — as attested by wide experience and much exper- 
imentation, — bears directly on the alleged demerit of chloride of 
potassium. The point has been forcibly presented by Mayer. By 
neither of these compounds, as he argues, is food offered to plants 
in ‘a proper chemical form.” 
It has been repeatedly noticed in Europe, and urged as one 
* As noticed by Hellriegel and by myself. See Bussey Bulletin, 1. 283. 
+ ‘‘ Elements of Agricultural Chemistry,” p. 231. 
t Here given in brief, without the careful explanations and qualifications 
which will be found in the original paper. 
