On Crystalline Form and Chemical Proportions. 203 
Angles of the Crystals. 
Paes ee oe 
Pege |. ©. k,n 
B’: B returning . 112° 50’ 
2 ee ee ee 
pee: 2° Ve eed ee 
Said eae al ear Vile — a9 
Bi-phosphate and Bin-arseniate of Ammonia. 
If we add arsenic or phosphoric acid to ammonia till litmus 
paper be strongly reddened by the solution, and till it no longer 
precipitates muriate of barytes, we obtain crystals which do not 
change on exposure to air. The muriate of barytes is not pre- 
cipitated by these crystals, but the smallest quantity of ammo- 
nia produces a precipitation. They are consequently at the 
same degree of saturation as the bi-phosphate and bin-arseniate 
of potash and barytes; and they comport themselves, with 
solutions of metallic oxides, precisely as the bin-arseniate and 
the bi-phosphate of potash. These salts dissolve very well 
in water. Bin-arseniate and bi-phosphate of soda are not 
decomposed by ared heat. On mixing bin-arseniate and bi- 
phosphate of ammonia bruised, with the neutral phosphate of 
soda in excess, it is found, on heating the mixture, that the 
acid remains with the salt having soda for its base, and that 
the ammonia and the water are completely driven off. The bin- 
arseniate of ammonia consists, according to the atomic propor- 
tions of M. Berzelius, of Arsenic acid 72.30 
Ammonia . 10.77 -100.00 
Water .. 16.93 
The bi-phosphate of ammonia is composed, by the same autho- 
rity,of . . . . Phosphoric acid 61.79 
Ammonia . . 14.85 
Water. . . 23.36 
100.00 
We have here 3 proportions of water to 1 of ammonia. 
Of the Faces of the Crystals, and their relative Situation. 
The primitive form of these salts is an octohedron, with a 
square base; butitis very rarely met with. The form under 
which they usually occur is a prism with square bases termi- 
nated by the faces of the octohedron (Fig. 2. D’, P.) No other 
modification has been observed either in the phosphate or ar- 
seniate of ammonia, although a great number of crystals ob- 
tained from different solutions have been examined. The in- 
clination of 7 upon Z is by measurement 90°; and the inclina- 
tion of the plane P upon one of the adjoining planes, is equal to 
that of P, on the other adjoining plane. The inclination of the 
plane P, on the plane P, situated on the other side of the axis, 
