PH O
PH O
( 218 )
fmell. It is capable of the concrete form un-der certain circumftances. When produced bycombuftion in the way already mentioned itappears in cryftalline flakes but very deliquef-cent: the liquid acid alfo when of 2- fp- gr. ifkept for feveral days at 32° or thereabouts willgradually depofit fmall needled cryftals. 1 Evenin fummer this takes place when quite at reft,but in a longer time.
Phofphoric acid is entirely unaltered andfixed in the fire. When the liquid acid isheated, it firft parts with its water, then, con-tinuing the heat, it becomes a clear gelatinousmafs, and at laft when the heat is raifed to red-nefs it bubbles and fwells, and finally fettlesinto a clear colourlefs acid glafs. This how-ever is again foluble in water and returns to itsformer ftate. The gelatinous acid is extremelydeliquefcent, and the vitreous acid in fome de-gree, and by expofure to air they both returnto the ftate of the un£tuous liquid acid. Thevitreous acid is a very powerful flux for allearthy and many metallic fubftances, andftrongly atts upon earthen crucibles, fo that infact it can hardly be obtained abfolutely pure,unlefs melted in a platina crucible. The phof-phoric and the boracic acids refemble eachother fo ftrongly in their unalterability in anyfire, and their powerful action as a flux, thatthey have been thought to be the fame fubftanceunder fome modification •, but no experimentshave as yet confirmed this opinion.
This acid is not afted on by hydrogen orfulphur, but charcoal decompofes it entirely ina ftrong heat, as is feen in the procefles for thepreparation of phofphorus defcribed under thatarticle.
The combinations of this acid with the feve-ral bafes are defcribed in the following article.
PHOSPHAT.S and PHOSPHITES.
The falts formed by the union of the phof-phoric acid with the feveral bafes are calledPhofphates, thofe with the phofphoreous acid,Phofphites. The former of thel'e will be firftdefcribed.
There are fome circumftances belonging tothe phofphates in general, which may be pre-vioufly mentioned. They are all, except theohofphat of ammonia, fixed in the fire, andreadily run into a glafs by a red heat. Thephofphat of ammonia lofes entirely its alkali,and when kept in fufion for a little time purephofphoric acid is left.
A remarkable circumftanee in which thephofphats differ from the fulphats, is, that the
» Guerfen in Phil. Mag. vol. 17.
former are not decompofed by calcination withcharcoal, which feems to have no effeft onthem. The phofphoric acid however is com-pleatly decompofed by this method, and alfothe phofphat of ammonia, but the latter onlyon account of the volatilization of the alkali,which leaves the acid naked. Hence phofpho-rus can be made direftly only from the phof-phoric acid or phofphat of ammonia.
With many of the bafes this acid unites inmore than one proportion, forming with thefame alkali and the fame acid, falts differingextremely in folubility and fenfible qualities.
Many of the other acids decompofe the phof-phats partially or totally.
When phofphoric acid and potafh are inmutual faturation, a fait is produced which isuncryftallizable, but when evaporated fuffici-ently paffes into the ftate of a thick jelly whichis deliquefcent in the air. It is therefore ex-tremely and almoft indefinitely foluble in water;when heated it fwells and bubbles till it hasparted with its water, after which it meltsinto a clear colourlefs glafs. It is decompofedby the fulphuric, nitric, and muriatic acids, andby lime, barytes, and ftrontian, fo that if alittle lime-water, for example, be dropped intoa folution of this, or any other alkaline phof-phat, a white precipitate of phofphat of limetakes place. Its conftituent parts are notknown, nor is it ufed.
Sub-Phofphat of Potajh. This variety was firftnoticed by Darracq, b and occurred in repeatingfome experiments on the fuppofed decompofi-tion of the alkalies. On heating to vitrificationa mixture of two parts of oxymuriat of potafhwith one of phofphoric acid, and digefting themafs in cold water, a white infoluble granularfubftance is left, which was miftaken for phof-phat of lime, but is in reality the phofphat ofpotafh in queftion. By evaporating the folutionand again calcining, more of this granular fub-ftance is left behind on digeftion with water,and thus by four or five procefles the whole isconverted to this phofphat.
The fame fait may alfo be produced in afhorter way by fufing in a platina crucible neu-tralized phofphat of potalh with an excefs ofpotafh.
This fub-phofphat is infoluble in cold water,but diflolves in a fmall degree with a boilingheat. It is extremely fufible and melts beforethe blow-pipe into a perfect bead of glafs, whichis tranfparent whiift in fufion, but becomes* An. Chim. tom. 40. p. 177.