182 SCIENCE PROGRESS 



agricultural purposes. Bearing in mind the fact that the 

 strength of sewage depends upon various factors above men- 

 tioned — e.g. the presence of rain- and storm-waters, etc. — it may 

 be roughly calculated that " ioo tons of sewage are worth 17s., 

 or in other words 2d. per ton. The value of the whole of the 

 excretal refuse of one person is put at 65. 8d. to ys. per annum. 

 Further it may be stated that 855 tons of sewage of average 

 composition contain one ton of solid matter in solution or 

 suspension, estimated to be worth £y 55. \d? From these data 

 one can calculate very roughly the theoretical yearly value of 

 the sewage of any town. Many authorities — e.g. Sir William 

 Crookes — consider that the present methods of sewage disposal 

 in this country are wasteful and thriftless. The sewage of our 

 towns is of course an invaluable source of fixed nitrogen. Sir 

 William Crookes in 1898 calculated that we lost fixed nitrogen 

 to the value of £16,000,000 per annum by disposing of our 

 sewage into drains and watercourses ; and Baron Liebig, for 

 similar reasons, predicted some time ago that " nothing would 

 more certainly consummate the ruin of England than a scarcity 

 of fertilisers, which sooner or later must mean a scarcity of 

 food." The late Dr. Vivian Poore demonstrated the enormous 

 capacity possessed by the living humus of surface soil for 

 dealing with the excremental matter, and showed the excep- 

 tionally heavy crops of vegetables yielded by the soil of his 

 own garden when thus treated. These and many other facts 

 bring home to us some conception of the gigantic loss of our 

 potential food supplies sustained by our water-carriage system 

 for the removal of sewage. But against this loss must be 

 pitted the vast saving of life and improvement in the health 

 of the people which we owe to the water-carriage system. 

 Furthermore the loss of fixed nitrogen entailed by this system 

 is not necessarily to be looked upon as continuous. Chemistry 

 has, we believe, already discovered a method of recovering the 

 loss ; but it would be premature to say that it is economically 

 practicable. 



The Disposal of Sewage 



The history of sewage disposal up to a recent date is a long 

 category of failures, coupled with an enormous outlay of public 

 money. But all these failures have been instructive, and it 

 would appear that at last we have fairly grasped the true 



