Phosphatic Materials used for Agricultural Purposes. 25 



usages less abrupt, phosphoric acid, equal to say 74 or to 76 per 

 cent, of tribasic phosphate of lime, as the case may be. If this 

 suggestion were generally adopted, all squabbles respecting the 

 composition of bone-earth would be set aside. By stating the 

 amount of phosphoric acid which was actually found in the 

 analysis, and the corresponding percentage of tribasic phosphate 

 of lime, it would be seen at once that a reliable method, and not 

 the uncertain process of precipitation, had been employed by the 

 analyst. 



The correct determination of phosphoric acid is attended with 

 a good deal of trouble, and necessitates much care and experience 

 on the part of the operator. 



The method of analysing bone-ash which I have adopted in 

 my laboratory yields most satisfactory results ; and, as it may be 

 useful to others, I will give a brief outline of it. 



Moisture and organic matter are determined as usual. About 

 twenty grains of finely-powdered bone-ash are carefully dissolved 

 in hydrochloric, or better in nitric, acid ; the solution is evaporated 

 to dryness in a waterbath. By this means any pyrophosphate 

 which may be present in the bone-ash is converted into the 

 ordinary phosphate, and the soluble silica which always occurs 

 in commercial bone-ash is rendered insoluble. The dry residue 

 is taken up in the smallest possible quantity of nitric acid, and 

 the sand filtered off; the solution passing through the filter is 

 heated to the boiling-point, and precipitated with an excess of 

 oxalate of potash or ammonia. The oxalate of lime held in 

 solution by the liberated oxalic acid is thrown down with the 

 first precipitate of oxalate of lime by neutralising the liquid with 

 caustic potash or soda, by adding afterwards an excess of oxalate 

 of potash or soda, and boiling. The oxalate of lime is removed 

 by filtration, and the filtrate and washings evaporated to a small 

 bulk, and finally the phosphoric acid precipitated with ammo- 

 niacal sulphate of magnesia. To prevent any oxide of iron or 

 alumina, which occasionally are present in commercial bone-ash, 

 from falling down with the phosphate of magnesia, it is desirable 

 to add a little tartaric acid to the liquid before precipitating the 

 phosphoric acid. 



The precipitated phosphate of magnesia has to be set aside 

 for at least twelve hours before it may be safely collected on a 

 filter. As an excess of oxalate of potash has to be used for the 

 determination of lime, and an excess of ammoniacal sulphate of 

 magnesia for the determination of the phosphoric acid, oxalate 

 of magnesia is formed, which, after standing for a time, 

 separates and falls down with the phosphate of magnesia, unless 

 a very large amount of ammoniacal salts is present. I find, 

 indeed, that the phosphate of magnesia obtained in this kind of 



