M. Donovan on the Freparation of Phosphorus. 203 



By the distillation of the phosphoric acid with charcoal, Wiegleb 

 obtained ten drachms and a half of phosphorus from two pounds 

 of bone-ashes. In the hands of Dolfuss, the same quantity of 

 bone-ashes furnished rather less than five drachms. Pelletier 

 sometimes obtained so much as 3^ ounces, and sometimes but 

 half that quantity from two pounds of bone-ashes. 



Although these methods may be thus epitomized, the prac- 

 tical details are very troublesome. It is not always easy to obtain 

 an adequate supply of bone-ashes. So truly did Lagrange ap- 

 pTCciate this difficulty, that in his instructions for burning bones, 

 he dii'eots. as the^^t step that a brickwork one yard in diameter 

 and nine inches high shall be erected. Others order a furnace 

 for the purpose, the chimney of which must necessarily be high, 

 in order to carry off the truly abominable fumes. When the 

 burnt bones are procured, the task of pulverizing and sifting 

 them, so that their substance shall be permeated and acted upon 

 by the sulphuric acid, is of no small labour, as the middle por- 

 tions of the cylindrical bones are exceedingly hard. The wash- 

 ing out of the phosphoric acid from the voluminous, pasty, and 

 somewhat tenacious sulphate of lime, is troublesome ; for much 

 of the acid obstinately adheres. If the sequel of the process be 

 to obtain the acid in the solid state, the evaporation of the various 

 washings to dryness is exceedingly tedious. But when lead is 

 employed to engage the phosphoric a(dd from the washings, the 

 resulting phosphate of lead is so bulky, so retentive of water, 

 and by the ordinary means so difficult to dry, that the increased 

 quantity of phosphorus procurable in this way scarcely compen- 

 sates the trouble and loss of time. Beside all this there is an- 

 other defect ; the precipitate, whether obtained from acetate or 

 nitrate of lead, contains lead in some state different from the 

 phosphate, more in the case of the former salt than of the latter, 

 and thus, during the distillation, the retort is partly occupied 

 with an unproductive material. The acid liquor, beside phos- 

 phate of lime, always contains a little sulphate of lime, great in 

 proportion to the quantity of water used in the washing; and 

 this gives origin to sulphate of lead, which not only uselessly 

 occupies the retort, but by suffering decomposition, during the 

 distillation with charcoal, evolves sulphur ; and this inquinates 

 the phosphorus produced to a certain extent. 



The precipitation of acetate or nitrate of lead by fresh urine, 

 and the distillation of the precipitate with charcoal, might to 

 some persons appear a convenient and simple process when large 

 supplies of urine can be procured at once, as in barracks, hos- 

 pitals, or prisons. But the advantage is far from being so great 

 as it appears ; for there are other substances present besides 

 phosphates, which will afford precipitates with salts of lead. In 



