274 How, When, and Where is Sewage Injurious ? :May, 
them. But as far as fish and other animals living in the 
waters are concerned, several other impurities found in 
sewage and in polluted rivers must not be forgotten. Fore- 
most come, perhaps, solutions of free chlorine and of the 
hypochlorites, such as bleaching-lime and bleaching-soda. 
When these liquids find their way into a river the fish are 
destroyed far and wide. The surface of the Medway, at 
Maidstone, is sometimes covered with their dead bodies to 
such an extent that the smell given off is exceedingly 
offensive. 
Of sulphur-compounds, which are also deadly to fish, I 
have already spoken. 
Lime, in its caustic state (quick-lime, slacked lime, lime- 
water), is well known as a fish destroyer. Its use has for ages 
been well known to poachers. Its application in the precipita- 
tion of sewage and the attendant dangers are too often over- 
looked. Even neutral salts, such as the sulphate of soda, 
the chloride of calcium, &c., if by any mischance they escape 
into a stream, may prove very destructive to fish, though in 
large rivers the quantity is rarely sufficient. 
We have next to consider what constituents of sewage, if 
any, are hurtful to plants. In the recent sewage of a resi- 
dential town there is nothing in the least hurtful to any of 
our cultivated plants, unless it is either supplied in too large 
a quantity or that it is too strong. Very few plants can 
bear repeated waterings with undiluted urine. 
But in the sewage of manufacturing towns there are 
abundance of constituents which, irrespective of quantity, 
destroy or injure trees, crops, &c., and have further a steril- 
ising effeCt upon the soil. As such must be mentioned 
waste bleaching-liquors, most sulphur-compounds, sulphuric 
and hydrochloric acids, solutions of alumina, iron (especially 
its proto- or ferrous salts), tin, lead, zinc, chrome, man- 
ganese, & c. Further, waters containing tannin, gallic acid, 
many coal-tar products, & c. 
Thus, the waste waters of paper mills, bleach, dye, print, 
and chemical works, metallurgical establishments, especially 
places where wire is “pickled,” and where the manufacture 
of tin or terne-plates is carried on. On the other hand, the 
waste waters of soaperies, glue and gelatine works, and some 
other establishments, are not to be feared. It will be at 
once seen that the profitable disposal of waters injurious to 
vegetation is an exceedingly difficult task, and that here 
“ irrigation ” is at once excluded. 
