P H O
P H O
( 222 )
by faturating phofphoric acid (arifing from theoxygenation of phofphorus by combuftion andnitric acid) with marble, is Hated by Klaproth 1to contain only 30.5 per cent, of acid.
The ufes of phofphat of lime are mentionedunder the article Bone .
Super Phosphat of Lime, or Jcjdu-lous Phosphat .
The preparation of this fait from bone-afhand fulphuric acid has been particularly men-tioned under the article Phofphorus , being thatacid fubftance which was generally miftakenfor pure phofphoric acid till the nature ofthis fait was explained.
When diftilled with charcoal all the excefsof acid, which makes the difference betweenthe neutral and the fuper-phofphat, is decom-pofed by the charcoal and yields phofphorus inproportion, and the neutral phofphat remainsin the retort.
The proportion of acid to lime, however,appears to vary confiderably, for Berthollet mfound that on walking with water the fuper-phofphat depofited during the concentration ofthe folution from bone-afh and fulphuric acid,it refolved itfelf into two portions, one of whichdifl'olved in the water and the other not.
This fuper-phofphat of lime is prepared withmoft accuracy by digefting phofphat of lime inphofphoric acid till it is faturated. This folutionyields the fait by evaporation in the form ofimall Ihining fcales or filaments* which havealmoft a gelatinous confidence, and a very fourtafte. This is the Hate in which the phofphatof lime is contained in frelh urine. This faitis fomewhat deliquefcent, is foluble in water,more in hot than cold, fo as to cryftallize bycooling. When heated it melts, fwells, andfinally vitrifies at a moderate red heat. Theglafs is opake till the fufion is compleat, and itthen becomes clear, fo that opacity is not aconftant fign of the prefence of lime, as hasbeen fuppofed. This glafs is not in the leaftdeliquefcent, is infipid, and infoluble in water,in all which circumftances it differs from thevitreous phofphoric acid. Charcoal decompofesit after being vitrified, as much as before, butprobably with more difficulty.
The acids probably do not a£t upon this faitexcept limply to diffolve it. All the alkalies andearths reduce it to the Hate of neutral phofphatby faturating the excefs of alkali, and caufethe phofphat to precipitate.
If a large quantity of alcohol is added to a
folution of the fuper-phofphat of lime it takesup much of the excefs of acid, without a pro-portional quantity of the lime; fo that theremainder is left in a ftate more approaching tothe neutral phofphat.
The compofition of this fait when preparedby phofphoric acid and phofphat of lime, ac-cording to Vauquelin , is 54 per cent, of phof-phoric acid and 46 of lime, and of this quantityof acid, about 32 parts are required to l'aturatethe lime in the proportions belonging to theneutral phofphat, leaving therefore 22 parts ofexcefs of acid, which alone can be decompofedby charcoal. Hence, according to this eftima-tion, 100 parts of the acidulous phofphat willyield no more phofphorus than can be obtainedfrom 22 parts of pure phofphoric acid.
This fait may be prepared either by faturatingphofphoric acid with carbonat of magnefia andevaporating to the cryftallizing point; or bydouble decompofition, by adding phofphat offoda to the fulphat or any other fait of mag-nefia. When the two latter are added in aconfiderably concentrated folution, after fomehours the phofphat of magnefia depolits intranfparent and irregular cryftals, and the clearliquor contains fulphat of foda.
This fait requires 50 parts of cold water forits folution, but lefs of boiling water. Thefulphuric, nitric, and muriatic acids, decompofeit entirely, as do the fixed alkalies, lime, barytes,and ffrontian, but ammonia only partially,forming a triple fait.
Phofphat of magnefia melts in a red-heatinto a perfedt glafs.
It is not ufed.
It is contained naturally in urine.
Phosphat of Ammonia and Magnesia.
This triple combination was difeovered byFourcroy in a calculus found in a horfe’sinteftine, and fince that time it has been de-tedted in the bones of moft animals in fmallquantity. The mode of analyfis is deferibedunder the article Bone . It is formed diredtlyby adding phofphat of ammonia, or ammonia,or its carbonat to phofphat of magnefia; and italfo is depofited by adding phofphat of foda toany triple ammoniacal fait of magnefia. Onthis fact Dr. Wollafton has fuggefted a conve-nient way of feparating and eftimating magnefiawhen in folution, with or without other earthsin any acid, which may be here mentioned.
Add to the folution in muriatic acid (for
1 Anal, EBay* vcl, %. p.164.
Chemical liatics.
Vauquelin.