PROCEEDINGS OF THE CHEMICAL DEPARTMENT. 213 



them, and they naturally prefer those which give immediate 

 results, of a kind calculated to assist them in the cultivation of 

 their own farms, to those which only add slowly to the general 

 store of knowledge, even though they should for this very reason 

 have a higher ultimate importance. The very circumstances 

 which deter individuals from undertaking experiments of this 

 kind are exactly those which recommend them to the attention 

 of an institution like the Highland and Agricultural Society ; 

 and when the subject of Field Experiments was taken up in the 

 year 1866, the Committee resolved that, in the first instance at 

 least, their efforts should be devoted to experiments of this de- 

 scription. Accordingly, the experiments of the first season were 

 devoted to the solution of certain fundamental points, and more 

 especially to determining the influence exercised by the particular 

 forms in which the different constituents of manures on their 

 fertilising effects. Thus, for example, it is believed that nitro- 

 gen, when in the uncombined state, cannot be assimilated by 

 plants, but that it is absorbed as ammonia. Many manures, 

 however, such as bones for example, contain no ready formed 

 ammonia, but a complex organic compound gelatine, which yields 

 that substance by decomposition, and it is only after that change 

 has occurred that it becomes available to the plant. In sulphate 

 of ammonia, on the other hand, the nitrogen exists in the very 

 state in which it is supposed to be absorbed ; and hence the ques- 

 tion arises, whether the necessity for a particular change occurring 

 retards the action of the bones, and makes them act more slowly 

 than they would do if they contained ready formed ammonia. It 

 is manifest that this is a matter of great practical importance, and 

 its solution one way or the other might often turn the scale in 

 favour of one or other of the forms in which the farmer uses 

 nitrogen. Of course, weather and the kind of crop to which the 

 manure is applied must manifestly exert a great influence on the 

 result. A dry season, which retards decomposition, and a crop 

 which requires abundance of nitrogen at the outset, are conditions 

 under which it may be anticipated that the ready formed ammonia 

 might surpass that which is not ready for assimilation, while a 

 wet season might put the two substances almost or altogether on 

 a par. Now, in all such experiments, the great point is to use 

 mixtures which shall be strictly comparable ; and in last year's 

 experiments this was accomplished by using a manure which 

 supplied the same quantities of soluble phosphates and nitrogen, 

 the latter being in one set in the form of ammonia, and in the other 

 entirely in that of gelatine as it exists in the bones. The sub- 

 stances used were sulphate of ammonia and glue {i.e. gelatine 

 identical in chemical nature with the nitrogenous constituent of 

 the bones), and these were applied in such quantity that the 

 nitrogen per acre was the same in both cases. The results of 



