M, Donovan on the Preparation of Phosphorus. 207 



vessels ; and the jelly which may be obtained from the residuum 

 is delicate and nutritious. 



When unburnt, crushed or unburnt broken bones^ whether of 

 beef or mutton, are to be used, provided they be of the dense 

 kind, I found that the quantity of '^ commercial nitrous acid " 

 requisite to dissolve the earthy matter is nine ounces and two- 

 fifths avoirdupois to one pound avoirdupois of bone. When the 

 same kind of bones have been burnt to whiteness, the ratio must 

 be 26^ ounces of acid to yone pound of bone-ashes. The acid 

 must in all cases be dilute^d with ten times its weight of water. 



If unburnt shaving^^of hartshorn be employed, each pound 

 .avoirdupois will require about 17 ounces of commercial nitrous 

 acTdr — This^^aeid^ is procurable at the price of about Qui. per 

 pound wholesale. 



With regard to the quantity of commercial sugar of lead re- 

 quired for the precipitation of the phosphoric acid contained in 

 bones, the following ratio will be found adequate. For unburnt, 

 crushed or broken bones, if not old, 1 pound avoird. will require 

 13 ounces. If bone- ash be used, 1 pound will require 41^ ounces. 

 For 1 pound of unburnt shavings of hartshorn, 1^ pound of 

 sugar of lead will be necessary. 



The cost of sugar of lead, wholesale, is about 5^. per pound : 

 but much of its expense may be saved in the following manner. 

 When nitrous solution of bone or hartshorn is precipitated by 

 means of sugar of lead, the phosphoric acid seizes on the oxide 

 of lead, and the nitric acid combines with the lime. If the so- 

 lution be filtered and evaporated, nitrate of lime is obtained. 

 But the solution contains the acetic acid of the sugar of lead 

 employed ; and if it be boiled on carbonate of lead, which may 

 be purchased at M. per pound, a solution of sugar of lead will 

 be regenerated which will answer for a new precipitation. At 

 length the liquor becomes so rich in acetic acid, that on a large 

 scale of manufacture it will be well worth while to distil it for a 

 product of pure acetic acid. 



When the phosphate of lead is first separated, it contains ni- 

 trate of lime j from this it must be freed by washing, otherwise 

 some phosphoric acid will be regenerated at the expense of phos- 

 phorus during the subsequent distillation. 



The common process of drying the precipitated phosphate of 

 lead on the filter is tedious, troublesome, and inconvenient ; so 

 tenacious is it of water that it will long remain a thin paste. I 

 find the best mode of drying it is to transfer both filter and preci- 

 pitate to an iron pot, and to heat it until the matter fall to powder. 

 Any part of the paper that escapes burning may then be picked 

 out. The drying is thus easily and quickly accomplished. 



The phosphate of lead, when dry, is a voluminous powder : a 



