procuring Phosphate of Lime and Mcignesia. 291 



more than I expected. One portion dried in this way gave 

 by Will's method \'9i per cent, nitrogen, or nearly two per 

 cent.; a second quantity, dried at 212° F., gave only 0*88 ni- 

 trogen. Another portion, air-dried, when heated to redness, 

 gave only 41*19 per cent, of fixed residue. 



One pound of urine precipitated with lime-water gave, when 

 heated to redness, 19*92 grains of phosphate of lime and mag- 

 nesia. A second pound of more highly concentrated urine, 

 similarly treated, gave 32*38 grs. of the same substances. Both 

 quantities were urine in its natural state. It is clear that these 

 results can only be regarded as approximative, as urine varies 

 so much in concentration in every individual, according.to the 

 circumstances in wiiich it is produced. £ djiwsmirto 



The amount of phosphate of lime obtained froni a pound 

 of urine is, it must be confessed, by no means considerable. 

 When we reflect, however, what an immense quantity of di- 

 lute urine may be readily obtained from the common sewers 

 of some of our large towns, it is clear that this is a source 

 which might be made to furnish the fields with large quanti- 

 ties of the phosphates which are at present passing into the 

 riveis, and which thus, for a long time at least, remain un- 

 availing for agricultural purposes. In conclusion, I shall 

 shortly describe the way in which I believe the operation of 

 precipitating the phosphates may be most conveniently con- 

 ducted on a large scale. The urine, in the state in which it 

 passes into the sewers, may be collected in any suitable pond 

 or tank, and the lime-water, or what is still better, the milk of 

 lime, may be prepared in a second tank of much smaller di- 

 mensions situated on a higher level. The milk of lime should 

 then be run into the first tank containing the urine, and the 

 liquids well-mixed by agitation so long as a precipitate falls. 

 I gready prefer employing a slight or even a considerable ex- 

 cess of milk of lime, rather than lime-water; for though the 

 phosphoric acid in the urine is completely precipitated by 

 either reagent, lime-water produces a gelatinous precipitate 

 which does not subside so readily and is difficult to filter, 

 while milk of lime throws down a tlocculent precipitate which 

 is much more manageable. When the mixture of the lime 

 and urine has been left to repose for some hours, the precipi- 

 tate subsides pretty fully, so that three-fourths of the water 

 may be readily drawn off by means of a siphon. By remo- 

 ving a plug at the bottom of the tank, the remainder of the 

 water may be run off through any suitably constructed filter- 

 ing apparatus, and the phosphate of lime and magnesia ob- 

 tained as a bulky gelatinous mud. 



The mass may be rendered perfectly dry, either by exposing 



U2 



