PROCEEDINGS OF THE CHEMICAL DEPARTMENT. 157 



act as a manure, and the general conclusion to be drawn from 

 them was that, as a source of nitrogen, that substance was on the 

 whole equal to sulphate of ammonia, a result which it is scarcely 

 necessary to observe, could only be due to its rapid decomposi- 

 tion in the soil. 



Although the experiments admitted of no other conclusion 

 than that just referred to, it appeared very advisable to repeat 

 them during another year, partly because the season in which 

 they were made was an exceptional one, but still more, because 

 I hold that no final or absolute conclusions should, in a science 

 like agriculture, be drawn from a single series of experiments, 

 however exact or successful they may be. I therefore gladly 

 availed myself of the kindness of my friend, Mr R. J. Thomson, 

 Grange, Kilmarnock, to whom my best thanks are due for the 

 opportunity he has afforded me of again experimenting on the 

 subject, and the trouble he has taken in securing a successful 

 result. It was my wish that these experiments should have 

 been repeated on turnips as well as cereals ; but circumstances, 

 to which it is unnecessary for me to advert, rendered this im- 

 practicable ; and during the past year they were made on oats 

 and hay. 



Though thus restricted as to the crops, it was possi- 

 ble, so far to modify the experiments, as to make them 

 embrace a somewhat wider field. The comparison of ammonia 

 with uric acid is only a particular case of the more general^ 

 question of the accessibility of nitrogen in different forms to the 

 plant. If there be any truth in the idea that uric acid cannot 

 decompose and yield up its nitrogen in forms available as plant 

 food, it necessarily follows that those substances which do so 

 must differ in manurial value, according to the facility and 

 rapidity with which they undergo this change, and thus it would 

 be necessary to establish by elaborate and frequently-repeated ex- 

 periments the exact value to be attached to each nitrogenous com- 

 pound. It would even be possible that some nitrogenous com- 

 pounds may be of so inert a character as to be entirely incapable of 

 decomposition in the soil, and although it is probable that such 

 cases must be so rare as to be practically unimportant, it is quite an 

 open question whether there maynot be some whose decomposition 

 is so tardy as to affect, to some extent, their value to the farmer. 

 Bones, for example, contain no ready formed ammonia, but the 

 gelatine, which forms in general about 85 per cent of their 

 weight, yields it freely by decomposition,' and though there is no 

 doubt that sooner or later the whole of their nitrogen passes 

 into the available form, still the question remains whether the 

 necessity for this change taking place may not so far retard its 

 action as to detract to a greater or less extent from its value to 

 the farmer, and make it less suitable to his -purposes than the 



