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



water is much more difficult than that of minerals or other solid 

 substances, for the reason that whereas in the latter the chemist 

 will probably be able to have at hand any moderate quantity to 

 operate upon, in the former he will probably find not more than 

 30 or 40 grains of solid ingredients in each gallon of liquid ; and 

 as it is upon these ingredients that the examination is really made, 

 there is practically a limit easily reached to the quantity of 

 matter which can be brought under analysis. Now, when it is 

 further considered that the analysis will be made probably upon 

 a gallon of water, and that as nearly a c^uarter of a million gal- 

 lons run through the soil in the course of the year, it will be 

 seen how great an error may be introduced into any calculations 

 which are founded on an imperfect analysis. 



One grain of any particular substance in a gallon of water will 

 in fact amount on the whole drainage of an acre of land in the 

 year to 240,000 grains, or about 34^ lbs. 



Still more does this remark apply to such substances as are, 

 when even in considerable quantity, difficult of precise deter- 

 mination, as nitric acid and ammonia; and to ascertain the quan- 

 tity of which, in very minute proportion, is almost beyond the 

 present skill of the chemist. When the samples of drainage 

 water reached me I soon found that they contained nitric acid, 

 although sometimes in small quantity only. For the estimation 

 of this substance, in minute proportion, there was absolutely no 

 existing process ; and as it was obvious, from the beginning, that 

 a great deal of the interest of the subject would be dependent 

 upon the compounds of nitrogen, which are so very important to 

 vegetation, it became indispensable that some method should be 

 discovered, by which the small quantities of nitric acid in the 

 drainage waters might be accurately determined. To this ques- 

 tion I accordingly addressed myself, and in concert with my prin- 

 cipal assistant (Mr. E. O. Browne) succeeded, though only after 

 uninterrupted attempts for several months, in devising a process 

 by which very minute quantities of nitric acid can be most accu- 

 rately ascertained. I have given a full account of this method in 

 an Appendix to the present paper, but I call attention to the sub- 

 ject especially here, because it is well that agriculturists should 

 remember that the applications of a science are bound up inti- 

 mately with the progress of that science itself ; and that often it 

 becomes impossible to make a step in advance, which a superficial 

 observer might think easy enough, simply because that step pre- 

 supposes a state of knowledge or power in science which does 

 not presently exist. Thus in this case the acquisition of satis- 

 factory knowledge, with respect to the composition of drainage 

 waters for the purpose of agriculture, involved the necessity of a 

 new process of chemical analysis ; and whatever the time and 



