552 



samples were analysed ; the first being the permanent one, viz. that 

 cultivated for nine or ten successive years in the same plot of 

 ground ; the second, the shifting one, obtained from a plot which 

 had borne different crops in the preceding years ; and the third, the 

 standard, derived from a sample of average quality, grown under 

 natural circumstances, either in the Botanic Garden itself, or in the 

 neighbourhood of Oxford. These analyses were performed by Mr. 

 Way formerly assistant to Professor Graham, of University College, 

 London, and now attached to the Agricultural College near Ciren- 

 cester. 



The examination of the soils was carried on in two ways ; the 

 first, with the view of estimating the entire amount of their avail- 

 able ingredients ; and the second, with that of ascertaining the quan- 

 tity in a state to be taken up at once by plants, the available ingre- 

 dients being those which are soluble in muriatic acid ; the active 

 ones, those which are taken up by water impregnated with carbonic 

 acid gas. This portion of the investigation was conducted in part 

 by the author, and in part by Mr. Way, and has reference to three 

 subjects ; first, to the amount of produce obtained from the deficient 

 crops ; secondly, to their chemical constitution ; and thirdly, to the 

 nature of the soil in which the crops were severally grown. 



The plants experimented upon were spurge, potatoes, barley, tur- 

 nips, hemp, flax, beans, tobacco, poppies, buckwheat, clover, oats, 

 beet, mint, endive, and parsley. The only crop which seemed to 

 show the influence of root-excretions was Euphorbia Laihyris, which 

 would not grow in the same ground three years successively, al- 

 though the soil was found afterwards fitted for rearing several other 

 species of plants. In the remaining cases, there was in general a 

 marked difference between the permanent and the shifting crop, to 

 the disadvantage of the former; and where exceptions occurred to 

 this rule, they seemed capable of being accounted for by accidental 

 causes. The amount of each year's crop is given in a tabular form, 

 and their differences illustrated by diagrams showing the relation 

 between the two crops of each vegetable. 



The second part of the memoir commences with an account of the 

 method of analysis pursued by the author for determining the nature 

 and proportions of the ingredients present in the ashes of the crops 

 submitted to examination. This method was, in general, similar to 

 that recommended by Will and Fresenius in their paper published 

 in the 'Philosophical Magazine,' No. 169; but in determining the 

 amount of phosphoric acid, the following mode was adopted in pre- 

 ference to the one therein given. 



As the phosphoric acid would seize upon the iron in preference 

 to any other base, the amount of peroxide of iron present in the ash 

 was first determined by precipitating it from a muriatic solution by 

 means of acetate of ammonia. The weight of the precipitate gives 

 that of phosphate of iron, from which that of the peroxide of iron 

 may be readily calculated. This being ascertained, he proceeds to 

 determine the phosphoric acid by operating on a fresh portion of 

 the solution of the ash, into which a certain known weight of iron 



