158 On some Properties of the Phosphoric Acid 



quantities of phosphoric acid of froni 8 to 1 2 ounces, which 

 I was obhgcd to prepare during the course of the last sum- 

 jner, and wliich crvstalhzed, though more slowly than in 

 winter, in a temperature of from lo" to 16° of Reaumur. 



The whole mass of acid generally curdles into tallow-like 

 lumps, which exhibit signs of crystallization only at the 

 surface. I have, however, been able several times to obtain 

 the quantity of six ounces in needle^like crystals, which re- 

 sembled the acid of siigar, and \\hich remained unaltered 

 during the hottest davs of summer. 



3d. Acid of a less specific gravity I was not able to make 

 .crystaUize ; biU by the addition of more water it curdled in 

 |he course of some time into a thick irregular mass. 



it thence appears, that to make phosphoric acid crystal- 

 lize, it requires besides rest adeiireeof concentration, which, 

 according to its specilio grayitj', must be as 2 to 1 of distilled 

 water. 



jr. // does not appear to have been yet proved, iihethcr phoS" 

 phoric acid produces or not a precipitate in a solution of 

 ■nitrate of silicr. 



It is asserted in some Elements of Chemistry* that ni- 

 trate of silver is decomposed, and sutlers the phosphate of 

 silver produced to be separated from it as a white precipitate. 



Others t refer to the experiments of Margrafl':|:, who, by 

 .means of an acid prepared from salt of urine, precipitated 

 silver dissolved in nitrous acid in the form of white soft, 

 lumps. Morveau § asserts also, that silver is precipitated 

 from its solution in nitrous acid by phosplioric acid. 



Lavoisier ||, as far as I know, is the only person who has 

 denied this precipitation ;' and Morveau wonders how La- 

 voisier could assert that no precipitate is formed. The opi- 

 nion of so celebrated an (ihserver, however, was of so nmch 

 weight, that I was unwilling to entertain any doubt on this 

 subject without further proof. 



I therefore dissolved four gros of the cr\'stal3 of nitrate of 

 silver in a sufficient quantity of distilled water, and two 

 gros of concentrated phosphoric acid prepared by nitric acid 

 and phosphorus were added. 



At first, a quantity of small crystals which had a perfect 



* HermstaJt's Expcrirjieiual Chemic, part iii. p. 115. 

 ■f Grcr.'s Htndbuch der Ciiemic, stcond edit, pait ii. p. 168, 

 J Mnigritl's Clicniic^l Works, parti, p. 107. 

 ^ On rhf Acid S.ilts decomposed by Bourj;iit:t, vol. ii. p. 281, 

 jl L^vosiifs Chemical W'ork^, translated into German by Wcigel, 

 tqI. li. p. 4.18. 



rcscujblaace. 



