192 PROCEEDINGS OF THE CHEMICAL DEPARTMENT. 



There can be no question that an analysis, conducted in this 

 way, is defective, because it draws no distinction between the 

 portion of the nutritive constituents which dissolve easily, and 

 that which requires the long-continued action of the strong acid, 

 although the former must be much more important than the latter. 

 Neither can it be doubted, that the mineral matters which are 

 absorbed by the roots pass through the organs of the plant which 

 takes them up in a state of solution, and we are really forced to 

 admit that the roots must exercise a solvent action upon those 

 substances which we know to be almost entirely insoluble in the 

 water of the soil. Of the nature of this action we can at present 

 form no idea ; but whether it be caused by an acid or not, it must 

 unquestionably be due to a solvent of a far feebler character than 

 that which is employed in the analysis of a soil, and hence it may 

 very possibly happen that a portion of that which, from its being 

 soluble in hydrochloric acid, is considered to be available to the 

 plant, may only be partially so, a certain portion of it, which 

 yields to the strong acid, being nevertheless retained by a suffi- 

 ciently powerful affinity to resist the solvent action of the roots. 



What we especially require, is some mode of distinguishing be- 

 tween the more and less accessible parts of the soluble consti- 

 tuents of the soil, but it is far from easy to devise a plan by 

 which this can be accomplished in a satisfactory manner. In 

 commencing the analysis of the soils in which the Field Experi- 

 ments of 1866 were made, I was extremely desirous of having 

 some information on this point, and gave to it a great deal of con- 

 sideration. The plan which at once suggests itself, is to use 

 hydrochloric acid of different degrees of concentration, commencing 

 with it in a highly diluted state, and analysing the solution so 

 obtained, then using a more concentrated acid, and thus obtain- 

 ing any number of solutions which might be deemed advisable." 

 Having had occasion some years since to make a series of expe- 

 riments for a very different purpose, in which this method was 

 employed, I had satisfied myself that very great difficulty existed 

 in obtaining uniform results by means of it, and I thought it best 

 to avoid it, and to adopt instead the treatment of the soil with a 

 very feeble acid. For this purpose I selected dilute acetic acid, 

 and the results, though not all that could be wished, present 

 many points of interest. The quantity of substances dissolved 

 by it is much smaller than was anticipated, and it might probably 

 have been better to have used it in a more concentrated state ; but 

 having commenced with a particular acid, it was used through- 

 out the whole series, so that the results might be comparable 

 with one another. 



The exact method in which the analysis was conducted may be 

 shortly described. 



The soil was first spread out in a thin layer for some days, 



