202 Progress of Foreign Science. 
on being dried. The salts are purified by crystallization. 100 
parts of this bin-arseniate, according to Berzelius, consist of, 
Arsenic acid . . . 63.87 
Potasheine) >) SE ealsgen6 
Water} /omyeeeyans9197, 
100.00 
The bi-phosphate, according to the same chemist’s atomic pro- 
portions, consists of phosphoric acid 25.26, potash 34.56, water 
13.18. In these two salts, therefore, the relation of the oxygen 
of the base is to the oxygen in the acid as 1 to 5; and to that 
in the water as 1 to 2. 
The acetate of lead decomposes completely the bin-arseniates 
and the bi-phosphates, for the arseniate and phosphate of lead 
are insoluble in acetic acid; the precipitate is commonly a 
neutral salt, but we can never be sure whether the neutral salt 
is not mixed with subsalt. The precipitation by the muriate of 
barytes is exposed to the same difficulties. The best method 
is to determine the base. After having precipitated the acid 
by the acetate of lead, and separated the salt of lead by the 
filter, we throw down the oxide of lead in the excess of acetate 
added, by carbonate of ammonia. We then evaporate the 
filtered solution, and after expelling the ammoniacal salt, and 
decomposing the acetate, we obtain the base, combined with 
carbonic acid. If we have employed muriate of barytes, we 
must precipitate the barytic excess with sulphuric acid, and not 
by carbonate of ammonia, because the carbonate of barytes is 
not completely insoluble in water. It is better, however, to make 
the analysis with the acetate of lead. 
Of the Faces of the Crystals, and their reciprocal Situation. 
We obtain sometimes the primitive figure, which is an octo- 
hedron, with a square base (Fig. 1.)*, from a solution which 
contains more potash than that of the bin-arseniates or the bi- 
phosphates. The ordinary form under which these salts are 
presented is a prism, with square bases, terminated by the faces 
of the octohedron, (Fig. 2.) M. Mitscherlich has never ob- 
served any other modifications. He has found by his measures 
the inclination of the plane /, to the plane J’, to be 90°, and that 
of the face P, to one of the facettes which are situated near 
it, equal to the inclination which it has to the other of these 
faces. It follows that the primitive form is an octohedron with 
a square base. He has found, by more than 30 measures, both 
in the bi-phosphate and in the bin-arseniate of potash, that 
the inclination of the plane P, on the plane which is situated 
on the other side of the axis, is from 93° 30’ to 93° 50’, usuaily 
from 93° 31’, to 93° 40’. The axes of the octohedron are nearly 
as 2 to 3. 
_ * The figures belonging to this paper will be given, with its conclusion, 
in our next Number, 
