On Crystalline Form and Chemical Proportions. 417 
Of the Bi-phosphate and Bin-arsemate of Soda. 
We obtain this bi-phosphate or bin-arseniate by adding 
phosphoric or arsenic acid to a solution of the neutral salts, till 
the liquid no longer affords a precipitate with muriate of barytes. 
These two salts are very soluble in water; and hence will crys- 
tallize only from very concentrated solutions, which must be 
left a long time in repose, when they yield large crystals. The 
solutions of these salts comport themselves in the same manner 
with solutions of metallic oxides, as the other bi-phosphates and 
bin-arseniates. According to Berzelius’s atomic determination, 
100 parts of dry bin-arseniate of soda consist of 
Arsenic acid . * 78.66 
Sadat) sa this 2134 
And these, by our author’s trials, combine in the hydrated crys- 
tals, with 24.58 of water; or it ultimately is composed of 
Arsenic acid . . . 63.16 
Dadar inst ee); line are pr TS 
Water ns dim, . 4f>nslQutd 
The bi-phosphate consists, by Berzelius, of 
Phosphoric acid . . 69.54 
Soda test Us. on iy ei 86 
which, in the crystallized hydrate, unite with 35.57 of water— 
a quantity which Mr. M. considers as containing 4 times as much 
oxygen as the soda does. By Berzelius, this salt is composed 
in 100 parts of Phosphoricacid . 51.49 
BONA a) Aah Sus Dae 
Water ei) ante 0. eee 
It hence follows, incontestably, that this bin-arseniate and 
bi-phosphate of soda are in the same degree of saturation, and 
combined with the same quantity of water of crystallization : 
but their crystalline forms, as to their number, relative situation 
of their planes, and value of the angles, are entirely different and 
irreconcileable. He hence infers that the very same substance, 
composed of the same elements, combined in the same propor- 
tions, may affect two different forms, provided that peculiar cir- 
cumstances exercise an influence in the act of crystallization. 
If the relative position of the atoms which constitute a crystal is 
changed by any circumstance whatever, the primitive form will 
not continue the same*. The chemical and crystallographical 
researches relative to arragonite, which have so much occupied 
the chemists and philosophers of our day, have finally shown 
that arragonite and carbonate of lime contain the same substances 
combined in the same proportions, and that notwithstanding 
their form is absolutely different. He enters into some details 
to prove that the relation hetween arragonite, carbonate of lead 
and carbonate of strontian is the same as the relation between 
* Is not this mysterious modification of the theory fatal to its physical value? 
Vou. xIV. 2E 
