DR. DAUBENY ON THE ROTATION OF CROPS, ETC. 241 



comaiended by Dr. Ure, for the purpose of condensing the acid which might be dis- 

 engaged in vapour, and restoring it to the body of the vessel*. 



The liquor, after being filtered, was evaporated to dryness, so as to dispel the 

 greater part of the acid. 



The residuum was then treated with water, and an excess of ammonia was added, 

 by which the iron, alumina, and phosphate of lime were thrown down. 



The whole was then carried to dryness, and gently ignited, by which means the 

 greater part of the iron and of the alumina is rendered insoluble in dilute acids, which 

 take up the phosphate of lime. 



The solution was then treated with ammonia so long as any precipitate was thrown 

 down, and the latter digested with dilute alcohol mixed with sulphuric acid, by which 

 any alumina and iron that had been precipitated were converted into soluble salts, 

 whilst any lime in combination with phosphoric acid would remain as an insoluble 

 sulphate, from the amount of which, when well-washed and dried, that of the phos- 

 phate present in the soil admits of being calculated. 



After ammonia had thrown down the alumina, iron, and phosphate of lime, the 

 alkalies existing in the ash would still remain in the solution. 



The latter was therefore again evaporated to dryness, and the ammoniacal salts 

 driven off. 



The residue was then treated with water, boiled and filtered, after which a solution 

 of carbonate of ammonia, to which a little pure ammonia had been added, was intro- 

 duced into the liquor that came through. The remainder of the earths were thus 

 thrown down, and nothing remained in solution except the alkalies. After the am- 

 moniacal salts had been expelled by heat, the mixed chlorides of potassium and 

 sodium were separated in the usual way by chloride of platinum. 



Such then was the method pursued for determining the nature and proportions of 

 those ingredients, which, if not available for the purposes of vegetation at the present 

 time, may at least be regarded as likely to prove useful to them within no very distant 

 period, as being separable, by dilute muriatic acid, from the mass of the earth. 



The soil of that part of the garden, in which the experiments above detailed had 

 been conducted, varied in depth from three to four feet, and rested upon a stiff clay, 

 of which the subsoil in the valley of Oxford consists, wherever it is not overlaid by 

 gravel. 



It was chiefly made ground, brought in to elevate the level of the garden above 

 that to which the contiguous river rises during the winter floods, and about a year 

 antecedent to the commencement of the experiments it had been manured with stable 

 dung. 



I have already expressed my regret, that no analysis was made of it until the pre- 

 sent year, at which time the experiments had been already brought to a close. 



In a neighbouring part of the garden, which appeared to be similarly circumstanced 

 to that which had been set apart for the experiments, except that it had been recently 



* Journal of the Agricultural Society, vol. v. p. 617. 



