68 
PROFESSOR GRAHAM ON THE CONSTITUTION OF 
pitate 26*8 grains lost by ignition 14*5 grains, or one part of the precipitate contains 
0*541 volatile matter. For the ammonia, the volatile matter from 9*65 grains of the 
precipitate was sent over quicklime contained in a tube, so as to arrest the water. 
The loss, or the ammonia, amounted to 0*67 grain, or to 0*0695 of the precipitate. 
Hence this precipitate consists of 
Theory of Mg 2 NH‘P-f 2H+ 10 H. 
Anhydrous salt . . . 45*90 45*85 
Ammonia .... 6'95 6*98 
Water 47 15 47*17 
100 * 100 * 
From the manner in which this specimen of the salt was prepared, it should con- 
tain the maximum proportion of ammonia of which the salt admits, and yet that pro- 
portion is one atom only, and not two, as it was estimated by Riffault. A salt of 
the same composition was obtained from the same materials, omitting the caustic 
ammonia. In that case the product was not so abundant, and the mother liquor re- 
mained acid from the production of tribasic phosphate of water and soda, which has 
an acid reaction. When this salt, contained in a little retort, is heated in a very gra- 
dual manner to 212° by means of a water-bath, it is possible to distil over ten atomic 
proportions of the water without any ammonia whatever. Of the three atoms of 
water which remain, (the whole quantity originally present in the salt being thirteen 
atoms,) one appears to be combined with the ammonia in the formation of oxide of 
ammonium, while the other two are the constitutional water of the tribasic phosphate 
of magnesia and water. 
It appears, then, that this salt is not a double phosphate, or combination of two 
phosphates, but that it is formed from the tribasic phosphate of magnesia and water, 
by the substitution of oxide of ammonium for the basic water of that salt ; and it is 
a tribasic phosphate of magnesia and oxide of ammonium. The oxygen in the mag- 
nesia is double that in the oxide of ammonium. 
This salt is the type of a class of tribasic phosphates, in which the magnesia is re- 
placed by the other oxides, which are isomorphous with that base. Two of these 
salts were discovered and carefully examined by Dr. Otto of Brunswick # . 
Dr. Otto’s analysis of what we may call the tribasic arseniate of manganese and 
ammonia corresponds exactly with the analysis given above of the magnesian salt, 
except that he derives only twelve instead of thirteen atoms of water from his salt. 
The deficiency in the proportion of water found by him, I attribute to the use which 
he made of hot water in washing his salt. 
His analysis of the tribasic phosphate of the protoxide of iron and ammonia is par- 
ticularly interesting, as it proves that this salt is precipitated, containing no more 
than three atoms of water, or exactly of the composition of the magnesian salt dried 
* Journal fur Praktische Chemie von Erdman und Schweigger-Seidel, 1834, p. 409. 
