166 DR. K. ANGUS SMITH ON 



material of pure organic origin, and the ammonia is converted 

 into nitric acid, forming very soluble salts, easily washed 

 away. There is also in no artificial filter, a ready power by 

 which the phosphates can be eliminated. 



The mode of using liquid manure only, is in reality the fil- 

 tration by the use of a natural filter, the ground ; and in a 

 case like this, the success is complete. The ground has the 

 power of absorbing a certain amount of salts, especially if 

 united with organic matter, such as the phosphates often are, 

 and the surface to which the liquid manure is applied is so 

 great, that there is no danger whatever of losing much of 

 its value. Filtration on any practicable artificial scale will 

 not produce this result, but will allow much valuable matter 

 to be lost. 



The subsidence method and the artificial filtration are both 

 liable to another great objection, that the ammoniacal salts 

 are not taken from solution in the slightest degree. On the 

 Paris plan, the liquid from their highly concentrated manures 

 is used in the manufacture of ammonia and its salts, as it is 

 strong enough to allow of the expense of heating and dis- 

 tilling from retorts into acids which retain it. The slowness 

 of the process of ordinary subsidence is also an objection. 



There was proposed, it seems diflficult to know by whom at 

 first, a plan for precipitating with lime. There was a com- 

 mission appointed by Parliament to inquire into it. The pre- 

 liminary inquiry was held before Sir Henry de la Beche, F. L. 

 WoUaston, Richard Phillips, Esq., and Dr. Lyon Playfair. 

 In 1845, Mr. Wicksted proposed lime for precipitating sewage; 

 and Mr. Higgs, in April, 1846, took a patent for lime. 

 There is a dispute as to who was first in proposing this, but 

 I see that in 1846 also Dr. Stenhouse proposed a plan for 

 precipitating with lime ; so that, apparently, the well known 

 clearing property of lime has given rise to the idea in many 

 minds of using it for sewage, and these were published at 

 the time when the subject was very much occupying public 



