ON THE TREATMENT AND UTILIZATION OF SEWAGE. 153 



that it -was equally distributed over those acres— an assumption which, 

 although giving a fair average approximation in the totals, necessarily 

 often gives fallacious results in the particular instances, because, while 

 some portions of the land had been consolidated by previous dressings of 

 sewage, other portions sewaged at the same time were loose and hollow from 

 recent cultivation, and therefore absorbed very much greater quantities of 

 sewage. 



Table V. gives a summary of the totals of Table IV., and in addition the 

 approximate estimates of nitrogen corresponding to the approximate estimates 

 of sewage, and also the amounts of nitrogen contained in the various crops, 

 as calculated from proportions given by the best authorities. In all cases, 

 however, the grand totals may be relied upon, as where they were not 

 obtained by actual measurement they are (as, for instance,'in the case of the 

 weights of crops) the ultimate results of a very large number of carefully 

 obtained averages. 



Table VI. is also a summary of Table IV., but arranged according to the 

 crops instead of according to the plots. It will be at once seen, from the 

 remarks already made, that the separate total amounts of sewage, and there- 

 fore of nitrogen, assigned to each crop are much less reliable than the cor- 

 responding numbers for the plots ; but, as in the last case, the grand totals 

 (which are, of course, identical with those in the corresponding columns of 

 the previous Table) are either absolutely correct or very reliable. 



The important result to be deduced from the grand totals in these Tables 

 is, that of every 100 parts of nitrogen distributed over the farm during the 

 twelve months, 10-67 parts, or about one tenth, were found in the effluent 

 water; 41-76, or approximately four tenths, were recovered in the crops, 

 making together about half; and 47-57 parts, or in round numbers the 

 other half, were unaccounted for. Of this half a portion must have remained 

 in the soil; and as the average composition of the soil previously to the 

 application of the sewage was determined by the Committee (see Second 

 Report, to the Meeting at Liverpool), it is intended to determine the pro- 

 portion of this unaccounted-for nitrogen which actually does remain in the 

 soil at various depths. 



The Committee thinks it right to call attention prominently to the fact that 

 the above proportions (representing the manner in which the nitrogen of the 

 sewage was ultimately disposed of in the case of Breton's Farm, during the 

 twelve months to which the Tables refer) are, for the sewage and effluent 

 water, as absolute and exact as accurate gauging and careful analysis can 

 make them, and are, for the crops, calculated by means of the most reliable 

 published data ; they are, moreover, the final results obtained from a much 

 greater number of continuously applied observations over a greater area, and 

 with a much greater variety of crops, than have ever hitherto been scien- 

 tifically made. 



The two main results of practical importance which, from the evidence of 

 the observations, may be accepted as generally attainable are : — first, that less 

 than eleven per cent, of the total nitrogen applied to the land escaped in the 

 effluent water, and of that only a fractional percentage in an organic form ; 

 and, secondly, that upwards of forty per cent, was actually recovered in the 

 crops grown upon the land — a proportion which must be considered highly 

 satisfactory (especially when the extreme porosity of the soil and limited area 

 of the land are taken into account), as in the experiments of Messrs. Lawes 

 and Gilbert only from forty to sixty per cent, of the nitrogen applied in 

 solid manures was recovered in the crops within the season of application. 



1872. M 



