Composition of Waters of Land-Drainage and of Rain. 151 



and by plants (especially the former), that we must look for an 

 explanation of such natural phenomena. That the quantity of 

 ammonia in rain is greater tlian in drainage-water, which suf- 

 ficiently attests the absorbing power of the soil for this alkali ; 

 but that the nitric acid in rain does not account for the quantity 

 found in drainage even in the instances where it is present in the 

 smallest quantity. That in all probability this nitric acid is due 

 to the oxidation of the nitrogencms matter of manures, and espe- 

 cially takes place where such manures are of a nature to prevent 

 their perfect admixture with the soil. That, lastly, the practical 

 means which occur to us of preventing so important a loss, are 

 the more perfect admixture of manures Avith the soil by any 

 method which may best accomplish that end. 



I shall take leave of this subject, at present, by suggesting the 

 desirability, where it may be accomplished, of employing the 

 drainage-water of land highly manured, for the irrigation of 

 meadow land in its neis-hbourhood.* 



APPENDIX. 



Pkocess for Estimation of Minute Quantities of Nitric Acid. 



The difficulties of determining nitric acid with any great 

 degree of accuracy are v/ell understood, and no process has 

 hitherto been known which could successfully deal with the 

 small quantities which are found in rain and other waters. t In 

 the autumn of last year (1855), the process which is now to be 

 described first suggested itself to my mind, but it was not until 

 after repeated attempts, extending over several months, and after 

 numerous modifications, that I was able, in conjunction with 

 my friend and assistant, Mr. E. O. Browne, to bring it to a 

 satisfactory issue. The process itself is based on Professor 

 Bunsen's volumetric method for the examination of oxidizing and 

 deoxidizing agents by the means of iodides, but it depends for its 

 success upon a number of conditions, the fulfillment of which 

 constitutes its merit. Professor Bunscn no doubt sought to 

 include nitric acid amongst the other substances to which he 



* Such an employment of drainage (surface) waters is well known to exist at 

 Lord Hatberton's at Teddesley, and the Duke of Porthind's at Clipstoiic. Mr. Paine 

 informs me that the drainage-water of some of the fields, where analysis has 

 demonstrated so great a loss of nitric acid, produces the utmost luxuriance in the 

 grass of a meadow over which it is allowed to tlow. 



t I have already alluded in the foregoing paper to Mr. Villc's method of deter- 

 mining this acid, which, according to the report of tlie commission appointed to 

 examine the subject, is sound in principle and successful in practice. 



