198 ORGANIC MANURES. [VIII. 



"with water, and their amount ascertained by tlie decrease of 

 weight. The residue, insoluble in water, is then carefully 

 digested in nitric acid, saturated dropwise with aqua ammonia, 

 and when a cloudiness appears, treated with acetic acid to 

 redissolve the suspended phosphate of lime. 



A normal liquor is now prepared by dissolving 3.107 grm. 

 of pure acetate of lead in 50 cub. centimeters of water, that 

 amount of salt having been found by experiment to be equiva- 

 lent to 1 grm. phosphate of lime. The liquor must be slightly 

 acidulated with acetic acid, and then poured into a tall glass 

 cylinder graduated into 100 equal parts, so that each degree 

 may represent 1 centigramme of phosphate. 



The acetic solution of phosphate, prepared as above, is 

 mixed with this liquid until it assumes a yellowish tint, when 

 two-thirds of its volume of alcohol must be added to mitigate 

 the solvent power of the free acid upon the lead phosphate, 

 and the pouring of the test-liquor continued, very carefully, 

 until a drop of the mixture gives the greenish-yellow lead 

 reaction with iodide of potassium. The number of divisions 

 of the normal liquid required to bring it to this point denotes 

 the number of centigrammes of phosphate of lime contained 

 in the solution. 



4. Organic Manures. — The fgeces of animals alone, or mixed 

 with other organic matter which they cause to putrefy, have 

 been used as manures time out of mind, and their value uni- 

 versally attested. The great influence of their ashes or 

 mineral constituents has been investigated latterly, and has 

 almost led to a disregard of their organic contents, unless in 

 the form of a compound yielding up ammonia to the air. Too 

 much haste has been shown in these conclusions. We report 

 a few examinations of excrements, which are of value inde- 

 pendently of theory. 



Human Fseces. — Fleitmann, who carefully examined the 

 human fseces (Silliman's Journ. 1849), found their inorganic 

 contents, as follows : 



