CHEMISTRY. 187 



" (e.) Any liquid which, iu 100,000 parts by weight, contains, 

 whether in solution or in suspension, in chemical combination or 

 otherwise, more than 0.05 part by weight of metallic arsenic. 



" (/.) Any liquid which, after acidification with sulphuric 

 acid, contains, in 100,000 parts by weight, more than 1 part by 

 weight of free chlorine. 



" (#.) Any liquid which contains, in 100,000 parts by weight, 

 more than 1 part by weight of sulphur, in the condition either of 

 sulphuretted hydrogen or a soluble sulphuret. 



" (A.) Any liquid possessing an acidity greater than that which 

 is produced by adding 2 parts by weight of real muriatic acid to 

 1000 parts by weight of distilled water. 



" (i.) Any liquid possessing an alkalinity greater than that 

 produced by adding 1 part by weight of dry caustic soda to 1,000 

 parts by weight of distilled water." 



UTILIZATION OF SEWAGE. THE PHOSPHATE PROCESS. 



The process for the purification and utilization of sewage, pro- 

 posed by David Forbes and Dr. Price, is founded on the fact that 

 certain mineral phosphates, easily obtainable, especially those con- 

 taining aluminum, when in a hyd rated or freshly precipitated state, 

 eagerly combine with the organic matter contained in the sewage, 

 it being sufficient merely to agitate them in the most fetid sewage, 

 to deprive it of all its odor and color, even if tinctorial substajices 

 of great intensity be present in the solution at the same time ; 

 whilst the phosphate of magnesium combines with the ammonia 

 contained in the sewage, and precipitates it also in the state of the 

 double phosphate of ammonium and magnesium. 



The precipitate subsides rapidly, and the water drawn off is 

 quite transparent and colorless, and has so little perceptible taste 

 that it may be drank without repugnance, provided one can banish 

 from his mind the idea of the filthy source from which it was 

 obtained. The process is an extremely simple one, and requires 

 nothing beyond a reservoir for holding the sewage whilst it is 

 submitted to the operation. The phosphates are preferably added 

 in the state of solution in sulphuric or chlorhydric acid to the sew- 

 age, and their precipitation in the hydrated form, along with the 

 organic matter in the sewage, and with more or less of the ammo- 

 nia (dependent on the strength of the sewage and the amount of 

 time during which it. is allowed to stand), is instantaneously 

 effected by the addition of a small quantity of milk of lime, just 

 sufficient to neutralize the acid which holds them in solution ; the 

 deposit subsides rapidly, and the supernatant water may at once 

 be run off, and discharged into the river. 



In reply to two questions which would naturally be asked, 

 (1), Whether the water discharged after this treatment is suffi- 

 ciently pure to be permitted to flow into the rivers ; (2), Whether 

 the valuable constituents of the sewage have been precipitated, 

 Forbes says : "As regards the phosphate process, we do not claim 

 that the affluent water is by anything like as pure as the water 



