553 



dissolved in muriatic acid is introduced, in quantity more than suffi- 

 cient to unite with the whole of the phosphoric acid present. This 

 done, acetate of ammonia is added and the mixture boiled, when all 

 the peroxide of iron, whether combined with phosphoric acid or not, 

 is thrown down. From the weight of the precipitate, that of the 

 phosphoric acid present may be calculated, as both the amount of 

 peroxide of iron present in the ash, and that which was added sub- 

 sequently, are known, 



A report is then given of the analysis of the ashes of barley, of 

 the tubers of potatoes, of the bulbs of turnips, of hemp, of flax, and 

 of beans, all cultivated in the Botanic Garden ; and from the data 

 thus obtained, the quantity of inorganic matters abstracted from the 

 soil in ten years by the above crops is deduced ; and a table is given 

 showing the relation between the permanent and shifting crops, with 

 respect to their produce, the amount of inorganic matters, that of 

 alkali, and that of phosphates, contained in them. 



In the third part of his paper, the author considers the chemical 

 composition of the soil in which the above-mentioned crops were 

 grown. He states, in the first place, the method he adopted for de- 

 termining the amount of phosphoric acid present in the soil. 



An analysis is then given of the soil taken from a portion of the 

 garden contiguous to that in which the experiments were carried on, 

 and from one of the plots of the garden itself ; and from these data 

 a calculation is made, that the ground at present contains enough 

 phosphoric acid for nineteen crops of barley of the same amount as ~ 

 the average of those of the permanent crops, and of the same quality 

 as that obtained in IS^^. It was also found, that there was a supply 

 of potass sufficient for fifteen crops of barley ; of soda, for forty-five ; 

 and of magnesia, for thirty-four. When, however, we examine how 

 much of these ingredients is taken up by water containing carbonic 

 acid, the proportion of each is found to be much smaller ; and a 

 striking difference exists, in this respect, between the soil which had 

 been recently manured and that which had been drawn upon by a 

 succession of crops. In the first case, the quantity of alkaline sul- 

 phate obtained in the pound was 3'4 grs.; in the latter it varied from 

 0*7 to 0*07 ; and of phosphate, the quantity in the former was about 

 0*3, whilst in the latter it varied from 0-18 to 0*05. 



From these facts the author concludes, first, that the falling-off of 

 a crop after repetition depends, in some degree, on the less ready 

 supply of certain of the inorganic ingredients which it requires for 

 its constitution ; but that two crops equally well supplied by the soil 

 with these ingredients may take up different quantities of them, ac- 

 cording as their own development is more or less favoured by the 

 presence of organic matter in the soil in a state of decomposition. 

 • Secondly, that it is very possible that a field may beun product- 

 ive, although possessing abundance of all the ingredients required 

 by the crop, owing to their not being in a sufficiently soluble form, 

 and therefore not directly available for the purposes of vegetation : 

 so that, in such a case, the agriculturist has his choice of three 

 methods ; the first, that of imparting to the soil, by the aid of manure, 



