OXALATES, NITRATES, PHOSPHATES, SULPHATES, AND CHLORIDES. 
67 
of experiments which I have performed it appears probable (although I have never 
attained very precise results) that the other six atoms go off in pairs at different tem- 
peratures between 212° and 350° Fahr. But even at 410° the quantity of water re- 
tained by this salt was sensibly above one atomic proportion. We may with consi- 
derable probability represent the consecutive combinations of this salt with water by 
such a formula as the following : 
Mg 2 HP + 2H + 2H + 2H + 8H. 
Besides the preceding salt there is a tribasic phosphate of magnesia, which is ob- 
tained as an insoluble precipitate on mixing tribasic phosphate of soda with sulphate 
of magnesia. Of this salt the whole three atoms of base are magnesia, as its name 
implies. Dried at 212° it retains five atoms of water. At a red heat it glows, but it 
continues soluble in acids even after exposure to a white heat. But I did not succeed 
in forming the other tribasic salt, containing two atoms of water and one atom of 
magnesia as bases, which is wanted to complete the series. Such a salt does not ap- 
pear to exist. 
It may be mentioned here in reference to the monobasic phosphate of magnesia 
(metaphosphate of magnesia), that although this salt does not present itself on mixing 
the monobasic phosphate of soda with the sulphate of magnesia, yet it is readily pre- 
cipitated in the form of a soft viscid body, on using the acetate of magnesia instead 
of the sulphate. 
4. Tribasic Phosphate of Magnesia and Ammonia. (Ammoniaco -magnesian Phosphate .) 
Mg 2 NH 4 P -f 2 H + 10 H. 
This salt is the well-known granular precipitate formed on adding a salt of mag- 
nesia to any soluble tribasic phosphate with which ammonia or a salt of ammonia has 
been mixed. I was much interested in ascertaining the true constitution of this salt, 
and have carefully analysed seven or eight different specimens of it, prepared with 
and without free ammonia in the liquors. The result is that only one tribasic salt of 
these constituents exists, although two have often been admitted ; while in this com- 
pound there exists only one atom of ammonia instead of two, as M. Riffault has 
supposed. I subjoin the preparation and analysis of one specimen of this salt. 350 
grains of crystallized phosphate of soda, 100 grains of chloride of ammonium, and 
200 grains of aqua ammonite were dissolved together in four pounds of cold water, 
and 200 grains of crystallized sulphate of magnesia were added to that mixture. The 
precipitation was gradual, and the liquor remained alkaline. The precipitate was 
slightly washed with cold water, and afterwards dried in the air for ten days, the 
thermometer being 65° Fahr., without artificial heat. The true proportions of water, 
which this and many other precipitates affect, have often been mistaken, and definite 
hydrates not obtained, from using hot solutions in their preparation. Of this preci- 
