206 M. Donovan on the Preparation of Phosphorus, 



After the nitrous solution of the earthy salts has been obtained, 

 the next step is to detach from it the phosphoric acid. This can 

 be done in the usual manner by a salt of lead. Chloride of lead, 

 although successful in the process of Henckcl and Marggraff, 

 does not answer here ; for a boiling solution of it added to the 

 nitrous solution does not produce any precipitation ; and chloride 

 of lead crystallizes as the mixture cools. Nor will nitrate of 

 lead occasion a precipitate ; for the phosphate of lead, if it be 

 formed at all in this case, remains in solution in the free nitric 

 acid. Acetate of lead answers the purpose perfectly : if a solu- 

 tion of it be poured into the nitrous solution of phosphate of 

 lime, phosphate of lead precipitates instantly. 



It has been stated by Giobert that when acetate of lead is^ 

 poured into a solution obtained by acting on bone-ashes with di- 

 lute sulphuric acid, the acetate is decomposed, not only by the 

 phosphoric acid, but, as he believes, by the water ; and he adds, 

 that the precipitate not only contains phosphate of lead, but calx 

 of lead, which adds materially to its quantity. He'further states 

 that nitrate of lead comports itself in the same manner but in a 

 less degree ; and hence he recommends the employment of ni- 

 trate of lead for detaching the phosphoric acid. In the pro- 

 cess recommended by me, as the precipitation takes place in a 

 liquid which contains a considerable quantity of uncombined 

 nitric acid, the objection of Giobert to acetate of lead cannot 

 apply. 



As to the choice of one amongst these different sources of 

 phosphate of lime, circumstances must decide. If the process 

 be conducted in the large way, bones ground between crushing 

 rollers, or even broken into moderately small bits, will be found 

 to answer, and to be the cheapest form : the cartilage that re- 

 mains may be converted to many oeconomical uses, for instance, 

 the making of glue, or of an excellent size. If bone-black be em- 

 ployed, according to the process already described, the residuum 

 is animal charcoal, which, after being washed and heated, is va- 

 luable as a decolorizing and antiseptic agent. If powder of 

 burnt bones must be used, there is no incidental advantage, but 

 the difficulty and trouble of minute division are to be encoun- 

 tered. The bones in burning ought not to be exposed to a very 

 violent heat ; for they lose a little phosphorus, as appears by the 

 white light which issues from them ; and besides this, they suffer 

 a certain degree of vitrification, which renders them refractory 

 under the pestle and to the action of acids. When the quantity 

 of phosphorus to be made is small, and a little additional cost is 

 no object, the unbumt shavings of hartshorn will perhaps be 

 preferred. The phosphate of lime may be dissolved out of them 

 by means of dilute commercial nitrous acid with facility, and in 

 a very short time ; the process is cleanly ; does not require large 



