6 SEWAGE AND ITS PURIFICATION 



hydrogen. Fragments of animal food putrefy and furnish a 

 product alHed to that from faeces. The amount of soap-water 

 varies with different days and times ; its advent is often con- 

 spicuous in sewages of small volume through the white 

 opalescence of the effluent, the alkalinity and odour — the latter 

 occasionally indicating scents or disinfectants. Household 

 discharges other than urine may also temporarily raise the 

 amount of chlorine. 



(c) Rain and Storm-water. 



(d) Grit and Detritus. 



(e) Manufacturing Waste Products. 



The entire refuse will in practice be separated into fractions, 

 which will differ in character according to the size of the 

 community and the system of disposal adopted. I shall have 

 occasion in Chapter VIII. to refer to the disposal of the grosser 

 solids. 



Street cleansing is also included in the general processes of 

 scavenging, and results in a semi-fluid mixture, which often 

 constitutes an important feature in the sewage. Besides the 

 wear and tear of macadamized roads (less from granite and 

 wood pavements, least from asphalt), together with the sand 

 used to prevent slipperiness, there is the great bulk of horse- 

 droppings, worked up by wheels into slush in wet weather and 

 ground into dust in dry. Four tons of these per day have 

 been stated to be gathered per mile in the Kensington Road. 

 Droppings should be collected fresh, and would then form 

 valuable manure, and the manufacture of much dust would be 

 prevented. In trading streets there is a serious addition of 

 animal and vegetable refuse, and the regulations for removal 

 are often unsatisfactory.^ Clothes are fouled by street dirt, 

 which is carried into houses in several ways, and has been 

 shown to result in contamination of food. 



The washings of roads contain abraded clothing and wood, 

 castings and emanations of men and animals, and particles of 

 soot, iron, earth, and stone, and are usually more impure, 

 especially from wood pavements, than an average sewage. 

 Samples taken during rain have contained i8 to 30 parts per 

 100,000 of chlorine, 2 to 3 of albuminoid ammonia in solution, 

 and as much as 80 to 120 of organic solids suspended and dis- 

 solved, all of which were formerly swept into the sewers, and 

 occasioned serious blocking and deposits. Before 1877 there 



^ See a debate on " The State of the London Streets," Sanitary Institute, 

 January 13, 1901. 



