DR. DAUBENY ON THE ROTATION OF CROPS, ETC. 211 



I shall, therefore, next proceed to state the results of the analyses of the several 

 crops which were made in my laboratory by Mr. Way. 



PART II. 



On the chemical composition of certain crops cultivated in the Botanic Garden, and on 

 the amount of inorganic principles abstracted by them from the soil during the period 

 the experiments were continued. 



It is only within a few years that the importance of ash analyses has been under- 

 stood, and we were consequently much at a loss for accurate instructions as to the 

 best method of conducting it. 



A valuable paper has however recently appeared in the Memoirs of the Chemical 

 Society of London (Part IX.), by Will and Fresenius, which in a great degree sup- 

 plies this deficiency, and which we therefore determined to adopt as the basis of our 

 scheme of operations. 



One part of it, however, relating to the determination of the phosphoric acid, was 

 soon found extremely troublesome in practice, and too tedious to be resorted to in 

 an inquiry which involved the necessity of so large a number of analyses. In this 

 part therefore of the process, Mr. Way suggested a method, which, as it recom- 

 mended itself from its greater simplicity, and appeared to answer well in practice, he 

 has adopted in all the cases, of which mention will hereafter be made. 



But although the plan of analysis pursued presents in other respects but little of 

 novelty, yet as certain modifications of the scheme of the German chemists have been 

 here and there introduced, and as some of the manipulations may admit of being 

 more clearly explained than in the paper alluded to, it will not be amiss to set down, 

 as briefly as possible, all the principal steps pursued for the determination of the several 

 ingredients existing in the ash. 



In a few instances, as in the Cerealia, where the ashes abounded in silicates, com- 

 plete solution in acids could not be effected, until the whole had undergone, either a 

 previous fusion with carbonate of barytes, or evaporation with caustic potass, the 

 former substance being employed for that portion of the ash which was to be ex- 

 amined for alkalies, the latter for the one set apart to ascertain the other ingre- 

 dients. 



But where the whole of the ash proved soluble in muriatic acid, no such prelimi- 

 nary process was required, and we were able to proceed directly to dissolve it in this 

 menstruum. 



A certain amount, however, of sand derived from the soil in which they had grown, 

 and of charcoal, from the organic matter of the plant which had not been burnt off, 

 was always present, and these of course would not be acted upon by this acid. 



There was also in every instance a variable quantity of peroxide of iron proceeding 

 manifestly from the vessels in which the combustion had been carried on, the quantity 



MDCCCXLV. 2 F . 



