416 Progress of Foreign Science. 
Of the Phosphate and Arseniate of Soda and Ammonia. 
We obtain these double salts by mixing phosphate, or arse- 
niate of soda, with phosphate, or arseniate of ammonia, in equal 
parts. The two double salts crystallize readily in their solu- 
tions (especially the arseniate) in crystals with brilliant faces. 
The phosphate is usually prepared by mixing muriate of am- 
monia with phosphate of soda; but we must then separate it, 
by repeated crystallization, from the adhering sal ammoniac. 
In crystallizing these two salts, a pertion of the ammonia is 
apt to fly off, and an acid salt is formed. For this reason we 
ought always to add a little ammonia, if we re-dissolve the crys- 
tals to crystallize them anew. These double salts comport them- 
selves with muriate of barytes, and the other solutions of metallic 
oxides, like neutral arseniates and phosphates. When heated, 
they lose only their ammonia and water, but no acid; and if 
what remains be heated along with carbonate of soda, the quan- 
tity of carbonic acid disengaged is equal to what the same 
weight of acid salt would have expelled. 
100 parts of the ignited salts were found, by experiment, to 
have been combined with 75.56 of water and ammonia. Ac- 
cording to Berzelius, the double phosphate consists in 100 parts 
of Phosphate of soda . . 31.95 
————— ammonia . _ 25.19 
Wate et SE BY 85S OO 
The primitive form of these two double salts is an oblique 
prism, with rhombic bases, usually modified by truncations on 
two edges of the prism. 
Of the Neutral Arseniate and Phosphate of Lead. 
These two salts fuse readily before the blow-pipe, and crys- 
tallize on cooling; a character which distinguishes them from 
the subsalts. They contain no water of crystallization, The 
oxygen of the base being to the oxygen of the acid as 1:23, 
according to Berzelius, they are composed ; 
The Arseniate of Arsenic acid . . 34.06 
Oxideoflead. . 65.94 
The Phosphate of Phosphoric acid . 24.24 
Oxide of lead . 75.76 
The analyses of different crystallized miatures of the phos- 
phate and arseniate of lead agree with the result of some trials 
quoted in Mr. M.’s first memoir, viz., that bodies which have the 
same crystalline form crystallize together, in every possible 
proportion. The crystalline form of the arseniate of lead, he 
finds to be identical, even in its modifications, with the phos- 
phate of lead, as described by M. Haiiy, (Traité de Minéralogie 
iii. 490). 
