{ 
_ diagram. 
March 16, 1894. 
a fair share to vulcanology alone. 
SCHENGE: 
groups of phenomena it is impossible for its holder to give 
So far the only chair 
of vuleanology was that of Catania, which was so well 
occupied by the late Professor O. Silvestri and which after 
his premature death was abolished. 
These are, therefore, the reasons 
course of lectures on yvulcanology 
Naples. 
why we shall give a 
in the University of 
My lectures will not be simply theoretical ones, 
for we shall make a number of excursions into the sur- 
rounding volcanic districts, where 
we can examine the 
phenomena and materials as they occur. 
STEREOCHEMICAL THEORY. 
BY T. PROCTOR HALL, PH.D., 
In the September number of 
TABOR, IOWA. 
the Journal of the 
Chemical Society Mr. S. U. Pickering points out that 
the fundamental idea of the tetrah 
atoms about a carbon atom is that of the 
edral arrangement of 
most sym- 
metrical arrangement of four spheres about a fifth cen- 
tral sphere, and that the same principle leads to a trian- 
gular arrangement about triad nitrogen and a hexagonal 
arrangement about pentad nitrogen. 
In the. case of the 
carbon atom this idea has proved so satisfactory that we 
are naturally anxious to see it tested in regard to all the 
other atoms. It is not, indeed, to 
be expected that the 
actual relations of atoms in three-fold space can be per- 
fectly represented by any theory 
which takes account 
only of such relations as can be expressed in a two-fold 
Hence, stereochemistry will inevitably become 
more and more prominent as our knowledge of molecules 
increases. It may be worth while, 
therefore, to consider 
more fully than appears to have yet been done the ar- 
rangements which the application 
of the same funda- 
mental idea require for other atoms having higher atomi- 
cities. In the following list the 
isomers of each kind is given. 
number of possible 
Ihave made no attempt 
to compare these with the facts; indeed that may not be 
possible as yet in many cases; but if the fundamental 
stereochemical idea is to be fairly tested, one of the first 
necessities is that the logical conclusions from it should 
be fairly and fully stated, and this I 
In the formule following M st 
atom, whose valance is given; A, 
have tried to do. 
ands for the central 
B, C, etc., stand for 
monoyalent elements or groups about M whose places in 
the diagram are indicated by the or 
in the formula. For 
der of their positions 
example, MBA,CB means that 
about M are grouped two atoms or groups of the kind A, 
taking the positions marked 2 and 3 
in the diagram, two 
of the kind B in the positions 1 and 5, and one of the 
kind C in the position 4. 
1. A Tetravalent atom may form the basis of two 
isomeric molecules, namely: 
z 2 
Miv 
{ ABCD 
(2) | ABDC. 
4 3 
2. Pentavalent atoms,—Hexahedron. 
My j AB, 
e (2) BA. 
ba 
BCDAD 
BCD, A 
BD, AC 
CD; AB. 
( ABCDE 
ABCED 
ABDCE 
ABDEC 
ABECD 
ABEDC 
ACDBE 
ACDEB 
ACEBD 
) ACEDB 
‘1 ADEBC 
ADECB 
BCDAE 
| BCDEA 
BCEAD 
BCEDA 
BDEAC 
BDECA 
CDEAB 
| CDEBA. 
3. Hexavalent atoms,—Oktahedron. 
M*i 
(6) 
My 
(5) 
PLA 
X 
> 
eee 
O 
> 
tS 
cae 
lols 
‘p> > 
ABCD, 
ABD, CD 
J ABDCD, 
ABD,C 
| ACD,B. 
ABCDEF 
ABEDCF 
ABCEDF 
ABDECF 
ABDCEF 
4 ABECDF 
and similarly 
E (six forms) 
D 
A 
A 
A 
A 
(C 
ABCBCA. 
B 
4. Heptavalent atoms,—Irregular. 
ce 
“cc 
ce 
M vi 
Mi 
(15) 
ABC, D, 
ABCD, C 
ABCDCD 
| ABD, C, 
ABDC, D 
ABDCDC 
AC, D, B 
~ACDCDB 
‘ ABCDE, 
ABEDCE 
ABDCE, 
ABECDE 
ABCEDE 
ABDECE 
ABCE, D 
ABE, CD 
| ABECED 
ABDE, C 
ABE, DC 
ABEDEC 
ACDE, B 
ACE, DB 
_ACEDEB 
147 
The nearest possible approach to a regular arrange- 
ment of seven atoms around one is perhaps that in- 
dicated in Figure 4, in which one atom is above M, three 
others are at the corners of a horizontal triangle and the 
