mf ijet si(fficlentli/ known, 16^ 



J»tred with sharp-pointed crystals, v.hich on closer examma»- 

 tion were found to consist of pure phosphoric acid. 



No furlhcr observations, however, as far as I know, wcrfe 

 made on this property of the {jliosphorie acid ; nor was "th4 

 crystallization of it in larger quantities ever remarked. 

 * Having been frequently employed in preparing pho3s» 

 phoric acid from phosphorus, I hrtd an opportunity to ob- 

 iserve that it possessed the following properties : 



1st. Four ounces of phosphoric acid, perfectly free from 

 nitric, muriatic, and sulphuric acid, as appeared on trying 

 it with a solution of silver, caustic Ihne, and a solution of 

 barytes, and the specific gravity of which, at the tempera=- 

 ture of 12° Reaumur, w-as to that of distilled water as 2-1, 

 shot up, bv rest, into feather-like crystals in the course of 

 a few wxeks, during which time the temperature of the at- 

 «josphere varied between + 2° and — l". 



This acid, having remained several days in a temperature 

 which varied from — 2° to — 8°, it curdled into an opake, 

 thick, tallow -like mass, in which no regular crystallization 

 was any more observed. 



To convince myself of the absence of siliceous earth, 

 which might have been taken up by the acid in consequence 

 of Its corTtinual contact with the glass, and w hich might 

 have produced this curdling, I took some of the curdled 

 acid, by means of a glass rod, from the glass in which it 

 was contained, and placed it on my hand, where by thte 

 heat it was immediately transformed into a fluid perfectly 

 transparent. 



On dilutinc it with two parts of distilled water, and sa- 

 turating it with carbonate of potash and of soda, no earthy- 

 precipitate was formed : T obs'er\'ed also, that the glass iri 

 which the acid had been kept showed no signs of having 

 been in the least attacked. These were sufficient proofs that 

 the acid was not rendered impure by siliceous earth. 



fid. An ounce of crystallized acid, which by heat had 

 been brought again to a fluid state, was exposed in- a small 

 glass tube to the temperature of — 3G° Reaunuir, produced 

 by a mixture of equal parts of snow and muriate of lime. At 

 the end of 15 minutes the mixture was taken from this ex- 

 posure to cold, as fluid as it was before the experiment : the 

 same acid in the course of some days, in the temperature 

 of — 2% returned to the same tallow-like consistence.- . 



It appeared to me to result from this experiment, that 

 the crystallization of the phosphoric acid is not produced 

 by a lo'.v temperature alone, but chieflv by rest. 



Ihir conjecture I found Irjly confirmed by several other 



(iuaiititic£ 



