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( 223 ) PHQ

example) fome fuper-carbonat of ammonia,(made by expofing the common carbonat to theair till it lofes its fcent) which will faturate theacid and precipitate the other earths, but notthe magnefia, being held diffolved by the excefsof carbonic acid. To the folution (which nowcontains muriat of ammonia and carbonat ofmagnefia,) then add a cold faturated folutionof phofphat of foda, and in a very Ihort timethe whole will be turbid with a white powder,which foon fubfides, and is the ammoniaco-magnefian phofphat.

Dr. MarcetP eftimates ioo grains of this faitdried at ioo® to contain 19 of magnefia.

This triple fait is fcarcely foluble in water,in which refpeft it differs remarkably from thefimple phofphat of magnefia. By heat theammonia flies off, and it is reduced to the fimplephofphat.

On diftilling it with charcoal it gives a littlephofphorus, owing to the decompofition of thatpart of the phofphoric acid which exceeds theproportion belonging to the fimple phofphat ofmagnefia in a given quantity of the fait.

The ftronger acids compleatly decompofe it,and naked phofphoric acid is left in the folution.The fixed alkalies and alkaline earths alfo de-compofe it, but by expelling rhe ammonia anduniting to the acid, in which cafe the magnefiais left uncombined.

PHOSPHITES.

Thefe falts refult front the combination ofthe Phofphoreous acid (already defcribed) withthe feveral bafes, and were frequently con-founded with the phofphats, owing to theindifcriminate ufe of the acid refulting from theflow combuftion of phofphorus and of the fullyoxygenated acid, till their characterilfic proper-ties were pointed out in a feries of experimentsundertaken by Vauquelin, and publifhed in theJournal de 1 ’Ecole PolytechniqueA

The phofphites have fome properties in com-mon by which they may be particularly dif-tinguifhed from the phofphats. The moltftriking of thefe is that they all yield a fmallquantity of phofphorus by dillillation withoutaddition, and when melted by the blow-pipeeven on an incombuftible fupport, they give°ut a very brilliant light, owing to the excefsof phofphorus burning off.

Thefe falts alfo precipitate gold from itslolutions in a metallic Hate, and detonate bypotafff* 011 ' when mixed with oxymuriat of

Their tafte alfo is not fimply faline like the1 Analyfi, of Brighton Water.

phofphats, but is mixed with fomething pungentand alliaceous.

It would be fuppofed from analogy with thefulphites, that the phofphites would Hill morerapidly than the latter falts, abforb oxygen fromthe air fufficient to compleat their acidification,confidering the great eafe with which the firftdegree of acidification takes place in the air.The contrary however takes place, for thefolutions of the phofphites may remain formonths in full contadl with the atmofpherebefore this change takes place, whereas the famechange takes place in the fulphites in a fewdays in fimilar circumftances. This differenceis ingenioufly explained by Vauquelin on theknown principle in chemical affinity, that anydecompofition is favoured by adding to thefubftances in aflion any body with which thenew compound has an affinity, and of courfethe ftronger this affinity is, the more readilywill the decompofition take place. Thus in theinftances here mentioned, the compleat oxyge-nation of the phofphoreous acid in the phofphiteis favoured by the affinity of the phofphoric acid(when produced) with the alkaline or earthybafis prefent, and the fame with the fulphureoitsand fulphuric acid. But both the actual affinityof the fulphuric acid with thefe bafes is ftrongerthan that of the phofphoric, and the differencebetween the affinity of the fulphuric and thefulphureous acids for the fame bafes is greaterthan that between the phofphoric and phof-phoreous, and it is probably from this canfethat the compleat oxygenation of the fulphitesis fo much quicker than that of the phofphats.

All the phofphites are readily changed tophofphats, either by applying a red heat, whichburns off the excefs of phofphorus, or bytreating with nitric or muriatic acid, whichcompleats their acidification.

The alkaline phofphites can only be preparedby the direcl combination of the bafe with thephofphoreous acid, and not, (like the fulphitesfrom the iulphats) by deoxygenation of thephofphats by carbonic matter.

The individual phofphites may be brieflynoticed.

Phosphite of Potash.

This fait eafily cryftallizes on cooling a hotfaturated folution of it, and takes the form of afour-fided prifm with a dihedral fummit.

It is foluble in three parts of cold water andlefs of boiling. When heated to rednels theexcefs of phofphorus burns off, and the refiduewhich is an opake glais, is foinewhat alkaline,

1 4th Cahicr. p. 655,