290 Dr. J. Stenhouse on an (Economical Method of 



transport to any distance, and any attempt to reduce it to the 

 solid state by evaporation, involves so large an expense for 

 fuel as to render it in most cases quite unadvisable. 



The method by which I purpose to procure phosphoric 

 acid from urine is not by evaporation, but by precipitating it 

 in the state of the insoluble phosphate of lime or bone-earth. 

 This is easily and cheaply effected, by merely adding a slight 

 excess of lime-waterj or still better, of milk of lime, to the 

 urine so long as it causes a precipitate. This precipitate, 

 when produced by means of lime-water, has a bulky gelati- 

 nous appearance, very much resembling alumina, and, as will 

 be seen by the subjoined analysis, consists of basic phosphate 

 of lime with a little magnesia and some organic matter. After 

 standing for some hours, the precipitate subsides pretty readily, 

 and the greater portion of the supernatant water may be easily 

 drawn off" by a siphon. The remainder may then be removed 

 by collecting the precipitate on any suitable filtering appara- 

 tus. On drying the precipitate, which, as we have already 

 mentioned, is very voluminous, it shrinks exceedingly. For 

 the purpose of obtaining this precipitate, it is by no means 

 necessary that the urine should be in a concentrated state ; I 

 have been able to procure it quite readilyfrom urine diluted 

 with ten times, or even more, of its weight of water. It is in 

 this circumstance that the chief advantage of the proposed 

 method consists, as urine can thus be made available as a 

 source of phosphoric acid, even in the very diluted state in 

 which it usually passes into the common sewers, when it has 

 hitherto been regarded as unfit for any useful purpose. When 

 the precipitate is destructively heated, it blackens, owing to 

 the considerable quantity of organic matter it contains; and 

 it emits at the same time a disagreeable ammoniacal smell, so 

 that it is by no means destitute of nitrogen. The organic 

 matter I believe to consist chiefly of mucus which has been 

 carried down by the lime. A quantity of this precipitate dried 

 at 212° F. was subjected to analysis. It gave — 



Lime 44-96 



Magnesia 1 '32 



Phosphoric acid 40'18 



Loss by ignition, organic matter and water 13'S4 



100-00 



As I have already mentioned, the precipitate when heated 

 to 212° F. gives off an ammoniacal smell, and consequently, 

 when it is meant to be employed as a manure, should be dried 

 at a very gentle heat. The quantity of nitrogen contained 

 in the precipitate, when dried at an ordinary temperature, was 



