470 .Mil. .1. It. LWVIX DE, GILBERT, ,\\l> DE PT7GH OR 



Nitrogen. Our preliminary investigations mil bave enabled us t<, avoid, or i" elimi- 

 nate, iill Bources of error due to the incidental circun of the research; and the 

 numerical results of a final series of experiments, showing the quantity abined 

 Nitrogen supplied, and those eventually found in connexion with the plant, will afford 

 the necessarj data for the solution desired. 



In discussing the conditions involved in the experiments, and the researches un< 

 taken to enable us to estimate the value of those conditions, we shall arrange the sub- 

 ject in such order as will most clearly hring out their bearings upon the main question, 



rather than according to the older as to time in which they were made. Several colla- 

 teral experiments were made, to prove that our conditions of growth, provided in soil, 

 atmosphere, and nutriment, were such as we had assumed them to he; tor had they not 

 been so, the object of the investigation could not be attained. The time required for 

 the conduct of these collateral experiments, made it necessary that many of them should 

 be performed simultaneously with the investigations the proper conditions of whi 

 they were designed to make known. 



We shall first consider the arrangement of the main experiments, and the plan and 

 results of the collateral inquiries with a view to show what the conditions of the former 

 should be, and then show how far the conditions assumed for the first year's exp< - 

 ments, and those arranged in the second year, after the results of some of the collateral 

 investigations were known, agree with the conditions indicated by the results of all the 

 collateral investigations taken together. 



Section I.— CONDITIONS REQUIRED, AND PLAN ADOPTED. IX EXPERIMENTS OX 

 THE QUESTION OF THE ASSIMILATION OF EREE NITROGEN BY PLAN - 



A. — Preparation of the Soil, or matrix, for the reception of the plant, and 

 of the nutriment to he supplied to it. 



In considering the subject of the soil to be used, the remarks made above on the 

 necessity of combining the conditions of healthy growth with the simplicity of constitu- 

 tion which would allow of a quantitative estimation of the results obtained, acquire a 

 high degree of importance. 



So complicated is the constitution of ordinary soils, and so intimately are the nitro- 

 genous compounds existing within them associated with the other matters, that it is 

 impossible either to estimate the Nitrogen with sufficient accuracy for our present pur- 

 pose, or to extract it from the soil without entirely destroying the other conditions of 

 vegetable growth. We are, moreover, so entirely ignorant of the character of the 

 organic constituents of soils, of the state in which the principal part of the Nitrogen 

 exists in them, of the changes to which it is subject during vegetable growth and 

 decay, and, more especially, of its relations to vegetable growth, that an ordinary soil 

 could not possibly be used for our purpose. 



Our ignorance of the actual constitution of soils, as regards the state of the organic 



