Toxcn Seioage. 475 



(A.) To check their estimates founded on the analysis of 

 the 24-hours' mixed sample of the Savoy Street sewage, 

 Messrs. Hofmann and Witt applied to an estimate of the amount 

 of urine daily voided by an adult the results of Berzelius' ana- 

 lyses of urine : for the fa?ces they took the record of the average 

 amount voided by the body-guard of the Grand Duke of Hesse 

 Darmstadt (but allowing, as they said, a little more for " John 

 Bull "), and the analyses of Way, Liebig, and Wesarg.. The 

 result so obtained for adult males they took as applicable to a 

 mixed population of both sexes and all ages, assuming that other 

 matters reaching the sewers would probably make up the differ- 

 ence — surely too libei'al an allowance for such " other matters." 



(B.) Some years later, in 1863, Dr. Thudichum, from much 

 more comprehensive data, gave for the iirine alone of an adult 

 male 15'9 lbs. of ammonia, an amount almost identical with that 

 of Messrs. Hofmann and Witt. 



(C.) But Dr. Thudichum considered that two adult males 

 would approximately represent 2"8 average persons, an adjust- 

 ment which reduces the estimate of these two authorities to 

 about 13 lbs. of ammonia, as shown in the Table. 



In 1854 Messrs. Lawes and Gilbert, basing their estimate 

 on very comprehensive data relating both to the food and 

 also to the urine and faeces voided by persons of all ages and 

 both sexes, set the ammonia at 10 lbs., and its manurial value at 

 Q)S. Sd. per head per annum. 



More recently, for the Sewage Commission, they revised their 

 estimates, bringing more recent information into account. 



Section (D.) is the record of the results so obtained.* 



The estimate, " according to food," was deduced from 86 

 dietaries arranged in 15 classes according to sex, age, activity 

 of mode of life, &c. From the result (12'2 lbs.) a deduction 

 must be made for the nitrogen retained in the body and for loss 

 in various ways. 



When the calculation was based on determinations or compu- 

 tations of the amount of constituents voided by different classes, 

 the result was 12'6 lbs., or, when of the amounts of fresh urine 

 and faeces taken at average composition, 12"7 lbs. of ammonia 

 per head per annum. 



* For nearly the whole, if not the whole, of the data upon which the new esti- 

 mates are based, see On the Sewage of London, by J. B. Lawes, F.R.S., 'Journal of 

 the Society of Arts,' March 9, 1855; The Composition of the Urine in Health and 

 Disease, by E. A. Parkes, M.D., I860; On an Improved Mode of collecting Excre- 

 mentitious Matter, loith a view to its Apjjlicafion to the benefit of Agriculture, &c., by 

 J. L. W. Thudichum, M.D., F.C.S., 'Journal of the Society of Arts,' May 15, 1863; 

 and On the Elimination of tfrea and Urinary Water, in relation to the period of the 

 Day, Season, Exertion, Food, &c., &c., by Edward Smith, M.D., LL.B., F.IS.S., 

 * Philosophical Transactions,' vol. cli. p. 747. 



