NIGHT-SOIL. 197 



In other manufactories of manure the night-soil, 

 whilst still soft, is mixed with the ashes of wood, or 

 with earth,* both of which substances contain a large 

 quantity of caustic lime, by means of which a com- 

 plete expulsion of all its ammonia is effected, and it 

 is completely deprived of smell. But such a residue 

 applied as manure can act only by the phosphates 

 which it still contains, for all the ammoniacal salts 

 have been decomposed and their ammonia expelled. 



The preparation of night-soil is now carried on 

 in London to a considerable extent. Owing to the 

 variable nature of the climate, artificial means are 

 employed in its desiccation. The night-soil, after 

 being subjected to one or other of the modes of 

 treatment described below, is placed upon iron plates 

 heated by means of furnaces. 



As soon as the night-soil is collected, it is placed 

 in large broad trenches, until a sufficient quantity is 

 accumulated for the purposes of the manufacturer. 

 But here it undergoes the same process of putrefac- 

 tion to which allusion has been made, and acquires a 

 peculiarly offensive smell from the evolution of sul- 

 phuretted hydrogen and other gases, which are 

 observed to escape. Unless some means be em- 

 ployed, at this stage of the process, to retain the 

 ammonia, it escapes into the atmosphere in the form 

 of a carbonate. Various methods have been proposed 

 to effect this purpose. Some manufacturers mix the 

 night-soil with chloride of lime, and evaporate off 

 the water by the aid of heat. This possesses the 

 advantage of depriving the excrements of smell, 

 and at the same time partially fixes the ammonia 

 which would otherwise escape. Chloride of lime 

 always contains a considerable excess of lime; hence 

 part of the ammonia contained in the night-soil is 

 expelled by means of it. 



More simple and economical methods might be 

 employed. A patent, which has been taken out for 



* This is practised in the vicinity of large cities in the United 

 States. 



17* 



