18}7.} during the Year 1816. 47 
consider the constitution of phosphorous and phosphoric acids as 
given in my paper on phosphureted hydrogen gas as likely to be 
accurate. 
6. Phosphate of Alumina.—When phosphoric acid exists in the 
mineral kingdom united to oxide of iron, the method of deter- 
mining its quantity hitherto followed consists in fusing the mineral 
with potash, and then precipitating the phosphoric acid by means of 
lime. Vaugquelin has lately pointed out an inaccuracy to which this 
method is liable. If the mineral contain at the same time phos- 
phoric acid and alumina, both will be dissolved by the potash, and 
both thrown down by the lime; so that the quantity of acid as de- 
duced from such an experiment will be erroneous. He proposes to 
correct this error by digesting the precipitate in potash, which will 
dissolve the alumina, and leave the phosphate of lime. Pure 
wlumina, when newly precipitated, is transparent and gelatinous ; 
while the phosphate of alumina is white and opake. But this change 
in the appearance of the alumina does not always indicate the pre~ 
sence of phosphoric acid. Silica and lime give it the same appear- 
ance. (Ann. de Chim. xevi. 213.) 
7. Phosphites.—Gay-Lussac has published an experiment to 
show that when a phosphite is heated it is converted into a neutral 
phosphate by the decomposition of the water which it contains, and 
that little or no phosphorus is disengaged. He prepared phosphorous 
acid by. the slow combustion of phosphorus, and saturated it with 
potash. This salt was put into a retort, to the beak of which was 
attached a bent tube dipping into water. The salt was heated 
rapidly. Hydrogen gas was driven off containing very little phos- 
phorus, for it had buta slight smell, and did not burn spontaneously 
when it came in contact with the atmosphere. (Ann. de Chim. et 
Phys. i. 212.) This is an experiment which L have often made, 
and it never succeeded with me exactly as described by Gay-Lussac. 
Davy some years ago ascertained that the gas driven off in this case 
was a — compound of hydrogen and phosphorus, to which he 
gave the name of hydro-phosphoric gas. Irom my experiments on 
this gas, 1 find that it is composed of two atoms hydrogen and one 
atom phosphorus. It does not burn when it comes in contact with 
air, but is easily fired by electricity or heat, and phosphoric acid is 
always formed during its complete combustion, Its smell is not so 
strong as. that of phosphureted hydrogen gas; but it is very remark- 
ble, and easily recognised. 
Berzelius, during his experiments on phosphorus, analysed two 
of the phosphites. I shall here state the results which he obtained. 
Phosphite of lead he found composed of 
Phosphorous acid ........ 191G .... 100 
Oxide of lead ...........' 77°69 ..., 405°45 
Water vide seat aie oe... BD 
10000 
