The Paris Sewage Irrigation at Ge inevilliers. 119 
It seems incredible that as the contents of the cesspools and 
the solid matter collected in the tinettes are not allowed to fall 
into the sewers — being carefully carted away to Bondy and other 
places — the Paris sewage should contain so large a quantity of 
solid matter both ir\ solution and in suspension. From the 
withdrawal of all solid excremental matter, it might be inferred, 
-on the contrary, that very little solid matter would be found. 
It has been ascertained, however, that no less than 15 lbs. of 
suspended solid matter is contained in 1000 gallons of the 
Paris sewage, besides 8 lbs. in solution, giving a total of 23 lbs. 
Some idea mav then be formed of the extent to which the 
warping of the river was carried,, and of the necessity, to which 
the municipal authorities were soon obliged to yield, of keeping 
steam-dredges at work along the reaches most affected by the 
sewage deposit. 
At the outfall of St. Denis the quantity of solid matter amounts 
to as much as 35 lbs. per 1000 gallons ; and some idea of the 
manuring value of the solid part of the sewage at that spot may 
be gathered from the following analysis : — 
lbs. 
Nitrogen If 
Combustible and soluble matter .. .. 14 
Mineral matter 19^ 
Total solid, per 1000 gallons ,.35 
No wonder that the dwellers on the banks of the river; and the 
navigators upon it, so loudly complained. By means of the 
drags, a most costly process, no less than 82,000 cubic metres of 
putrescent mud were removed every year ; but this was only a 
mitigation of the evil, and by no means a cure, inasmuch as the 
stench emitted by the heaps of this black fatty silt, removed by 
the drags, was greatly increased in intensity by being exposed to 
the action of the air and of heat. The cost of the dragging opera- 
tions came to about 7000/. a year. 
Owing to the limited quantity of sewage hitherto utilised by 
the Gennevilliers people, the drags are still at work ; but the still 
more costly and inadequate process of purification by sulphate of 
alumina has been altogether abandoned, to the great discom- 
fiture of the manufacturing chemist, whose factory was close at 
band, in Gennevilliers itself, and who supplied the sulphate of 
alumina at no small profit to himself. The supply of that 
chemical alone would have cost 40,000/. a-year, if the process 
had been persisted in. 
In the meantime, the Sewers Commissioners, assisted by those 
•eminent engineers, MM. Mille and Durand-Claye, were not 
idle in contriving other means of overcoming the huge diffi- 
