P H O

PH O

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opake on cooling. The proportions of its con-ftituent parts are not known.

Phosphat of Soda.

This fait is now the bell known of thealkaline phofphats, having been introducedin pharmacy by Dr. Pearfon as a very ufefulpurgative. It may be prepared in feveral ways.The fimpleft, but by much the moft expenfive(and therefore never ufed in quantity) is firft toprepare phofphoric acid by the combuftion oroxygenation of phofphorus, and then to addcarbonat of foda in excefs, to evaporate, andcryftallize. This fait is however actually pre-pared by adding carbonat of foda to the phof-phoric acid (or rather the acidulous phofphat oflime) procured by decompofing bone-afh by ful-phuric acid. The method of making this de-compofition has been defcribed under the articlephofphorus, and will be further noticed whentreating of Phojphat of Lime.

To obtain this fait pure, the fulphuric acidfhould not be more than is fufficient to decorn-pofe the bone-afh, and the fulphat of limefhould be allowed to precipitate by cooling (af-ter concentration of the acid liquor) before thealkali is added. The acid liquor is then to bediluted with fufficient water, and carbonat offoda added till there is a very fenfible excefs ofalkali, after which the folution is to be evapo-rated confiderably and fet by to cryftallize.The phofphat of foda then feparates in largewell defined cryftals, generally rhomboidal orprifmatic.

The mother water is then to be again evapo-rated, adding either foda or phofphoric acid,according as it is too little or too much alkaline,and a freffi crop of cryftals is obtained.

This fait naturally contains and requires anexcefs of foda, for when merely faturated itwill not cryftallize.

The quantity of phofphat of foda obtainedin general is about equal to the carbonat offoda employed.

Another and perhaps a cheaper way of pre-paring this fait is given by Mr. Funcke, aGerman chemift. 0 Add to bone-afh, diffufedin water, juft enough dilute fulphuric acid tofaturate the carbonat of lime which it alwayscontains in fmall proportion, which is knownny the ceffation of the effervefcence. Thendillolve the whole in nitric acid and add totne solution as much fulphat of foda as thequantity of bone-afh ufed. Diftill the whole

° r , r ^ n ? s ’ to rec °ver the nitric acid, and there t ueint ie retort is a mixture of phofphat of

’ ^il Joum. vol, 6. from Scherer’s Journal. * Pelle

foda and fulphat of lime, formed by the mutualdecompofition of the phofphat of lime and thefulphat of foda. The phofphat of foda is thenfeparated by folution and cryftailization mthe ufual manner. It is obvious howeverthat if too much fulphat of foda be added, theexcefs muft mix with the phofphat of foda.This admixture of fulphat of foda may bedetefhed by nitrat or muriat of barytes, whichforms a white precipitate with both falts, butthe phofphat of barytes is again decompofed,and forms a clear folution with nitric or mu-riatic acid, whilft the fulphat of barytes remainsuntouched.

Phofphat of foda has a fimply faline taftewithout any thing naufeous or bitter (in whichit differs from many other of the purgative falts)it (hews with vegetable colours the marks ofexcefs of alkali, it efflorefees in the air, butonly on its furface. d

It is one of the moll foluble of the non-deliquefcent falts, requiring no more than fourparts of cold water, and two of boiling, whenceit eafily cryftallizes from its hot faturatedfolution on cooling. It is compofed accordingto Thenard e of 66 per cent, of water of cryftai-iization, 15 of phofphoric acid, and 19 of loda,as determined from the following facts, namely,that 100 parts lofe 66 on calcination, and therefidue decompofed by muriat of lime give 33of phofphat of lime, of which the acid iseftimated at 15.

When heated, this fait melts in its ownwater, bubbles and boils up, and at laft, whenred hot, it fubfides into a glafs which beforethe blow-pipe is clear when hot, but on coolinggrows opake, and affumes nearly the form ofthe garnet. This fingular property it has incommon with the! phofphat of lead. f

The fulphuric, nitric, and muriatic acidsdecompofe it only partially, leaving in thefolution an aciduious phofphat of foda. Thefame is produced by adding phofphoric acid,and this fait is extremely foluble, fcarcely cryf-tallizable, and takes the form of fmall foftbrilliant threads, like boracic acid. ®

The phofphat of foda, befides its ufe in medi-cine, has been employed with fome fuccefs as afubftitute for borax, in the foldering of metals.

Phosfhat of Ammonia.

This combination is found in tolerable abun-dance in urine, but united with phofphat offoda, from which it is fcarcely poffible to fe-parate it, and therefore to obtain it pure, it muftbe formed by the direct union of its two fil-er. • An. Chim. tom. 39. ■ 1 Pelletier. « Fourcroy,.

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