424 PHOSPHORIC ACID. 



with 3 oz. of the common acid, produce 6 dr. of phosphoric acid. 

 The theory will be be given hereafter. 



3. PROPERTIES. 



(a.) Evaporated and heated to ignition in a platinum crucible, it 

 becomes white, firm and transparent, like glass. This is the pure 

 acid.* 



(b.) Deliquesces into a jelly ; soluble in water, the anhydrous 

 flakes dissolve with hissing ; the acid decidedly reddens the vegetable 

 blues ; it is very sour and almost corrosive ; it combines with bases 

 to form phosphates. It blackens oils. 



(c.) The glacial phosphoric acid is a hydrate, and the water can 

 not be expelled by heat, for if fully ignited, it rises in vapor with the 

 water. It used to be said that this acid is fixed at intense degrees 

 of heat ; this remark applies only to the impure acid ; still it endures 

 a considerable heat, and from its tendency to vitrify with earthy 

 bodies, it is a powerful flux, and is very effectual in decomposing 

 saline bodies, provided heat be applied. 



(d.) The deliquesced acid, on being heated in a platinum cruci- 

 ble, exhibits anew, after being cooled, the density and brilliancy of 

 the precious stones. f 



(e.) A great quantity of heat and light are liberated during the 

 combustion, which unites two substances, one a gas, and the other a 

 volatile odorous solid ; the phosphoric acid is inodorous and fixed, 

 and of great density, which implies great condensation. The dry 

 acid sublimes in close vessels ; a little water prevents this, but a larger 

 proportion carries up some of the acid with it when it is evaporated. 



(/.) A little heat is evolved when phosphoric acid of a spongy 

 consistency, is mixed with water ; the heat has varied from 1, to 

 more than 50, as the density of the acid was greater or less. 



(g.) Sp.gr. in glass 2.8516; in dryness 2.687; in deliques- 

 cence 1.417, 



(A.) Charcoal, at a red heat, completely decomposes the phospho- 

 ric acid ; carbonic acid gas is formed and the phosphorus sublimes, 

 and may be received by immersing the neck of the retort under 

 water. This is nearly the ordinary process for the extraction of phos- 

 phorus. 



(*".) Diamond produces no effect ; for it may be kept a long time 

 in the midst of phosphoric acid, at a red heat, without experiencing 



* In the process by nitric acid, some ammonia is formed by the union of the hy- 

 drogen of the water with the nitrogen of the acid, and it is driven off by the heat. 



t Chaptal says, " I observed once, to my great astonishment, that the phosphoric 

 glass I had just made, emitted very strong electric sparks ; these flew to the hand 

 at the distance of two inches. I exhibited this phenomena to my audience of pupils. 

 This glass lost the property in two or three days, though preserved in a capsule of 

 common glass." 



