Crystalline form and Chemical constitution. 91 
the prism J, and the domes 1-2, 1, respectively, 93° 40’, 104° 
22', 107° 54’; and the latter for the corresponding angles 93° 16’, 
96° 46’, 99° 50’. MnO? in the tetragonal state is unknown 
except when it is in combination with 2Mn0O, as in hausmannite. 
The protoxyd of manganese, MnO, it may be remar iS iso- 
metric, like , it having been obtained artificially in octa- 
hedrons and cubo-octahedrons by Deville (C. R., liii). 
Among artificial compounds, there are the following tetragonal 
species all conforming to the principle stated : 
KF+HF; BeS+4aq; NiS+%aq; NiS+6aq; NiSe+ aq; ZnSe+7aq; 
(K, HB; (Am, Hy; (K, H)?As; (Am, H)*As; GaO+2aq; (Am+H)B*+3aq; 
NaO, 107; KCl4+CuCl+2aq; AmCl+CuCl+2aq; AgS+2NH°, AgOr+2NH?, 
2K Ac (acetic acid)+CuS+12aq; CaXe+OuAc+8aq, KAc+26Ac+2aq, AgAc+ 
26 Ac+2aq; (¢Ca+$Hi)°T (tartaric acid, containing 50)-+-SbT +7aq. 
Omitting a few complex organic compounds, these are all the 
tetragonal species in the two volumes of Rammelsberg’s Crys- 
tallographic Chemistry excepting Agéi, Hg2cl. Other examples 
aoe be mentioned, but the above are fully sufficient. __ 
e correspondence with the law for tetragonal species is so 
general that we may reasonably believe that the apparent be 
ions, where the composition and crystallization are correctly 
given, may be brought into conformity to it by an application 
of one or the other of the following principles. 3 
a. The principle of polymerism.—Hg?Cl is Hg?Cl? in the new 
m of chemistry; and if the whole is doubled, it becomes 
“Cl*, which is probably the true formula of this species in 
onal state, the only crystalline state yet known. 
~ 
a 
a 
ot 
z 
8 
5 
“ 
: 
3 
A 
Ng 
g9 
a 
: 
5 
> 
: 
73 
3 
@ 
Of late been written by chemists admitting this. Apophyllite 
18 @ tetragonal species consisting of R+2Si+2H. Making the 
Water basic, there is still no conformity to the type of either the 
s or bisilicates, the oxygen ratio ae the bases and silica 
7 
being 8:4. If half the water be regarded as basic, and the 
fying the crystallization as determined by the other part. 
