ON THE TREATMENT AND UTILIZATION OF SEWAGE. 213 
Secrron I.—Fourth Note on the Dry Earth System. 
Dr. Gilbert has supplemented the results given in former Reports by the 
determination of the nitrogen (by the soda-lime process) in soil which has 
now passed through a Moule’s earth-closet five times. The determinations 
were made upon the air-dried manure; but, for uniformity and for fairer 
comparison, the percentage is, in each case, calculated upon the soil as dried 
at 100° C. The results of the series are as follows :— 
After | After | After 
Before | After | After using | using | using 
used. | USPS | USING | three four five 
times. | times. | times. 
Percentage of nitrogen in 
soil dried at 100°C. .... | 0-073} 0-240} 0-383) 0-446/| 0-540| 0-614 
Dr. Russell has also determined the quantity of nitrogen existing as nitrates 
in the soil in its present state—that is, after it had passed through the closet 
five times ; and he finds it to amount to 0°20 per cent. in the soil as fully dried. 
Supposing the whole of this to be in addition to that determined by the soda- 
lime method, the total nitrogen in the dried soil would be raised to 0-814 
per cent.—still, therefore, to considerably less than-1 per cent. in the fully 
dried condition, and scarcely ? per cent. in the air-dried condition. The 
Committee must again say “ ‘That such a manure, even if disposed of free 
of charge, would bear carriage to a very short distance only.” It may be 
observed, however, that the process of emptying was still unaccompanied by 
any offensive smell, and that the soil after drying on the floor of a shed 
could scarcely be distinguished from ordinary mould. 
The ztncrease in the percentage of nitrogen (determinable by the soda-lime 
method) in the soil, calculated as fully dried, by each use was as follows: — 
After | After | Que | After | After 
using | using nines || fede o|o “eee 
ir. three four five 
once. 1Ce | times. | times. | times. 
Increase in the percentage of nitro- 
gen in soil dried at 100° C. .... | 0°1670| 0-1427)| 0-0626) 0-0949) 0-0785 
The gain of nitrogen as ammonia or organic nitrogen was therefore 
considerably greater by the first and second than by either of the subsequent 
uses of the soil. The differences observed may probably be partly due to 
the differences in the length of time during which the manure was exposed 
to dry, and in the temperature of the periods—circumstances which would 
affect the degree of further change, and, as one result of this, the amount of 
nitrogen passing into the form of nitrates. The general result is, however, 
an average gain of total nitrogen of scarcely 0:15 per cent. by each pas- 
Sage through the closet. On this point it may be remarked that, if only 
two pounds of soil were used per head per day, and as much as one third of 
the total nitrogen voided in feces and in urine by an average individual in 
24 hours were collected with it in the closet, the nitrogen so added to the 
soil would amount to about 0-5 per cent. of its weight by each use, or by 
using five times to nearly 2-5 per cent. Probably in practice a larger 
