Chemistry and Physics. 67 
by a violent criticism from the great — _— Nats 
who never deigns to attack any but the most important theories. 
The principal points made by Van’t Hoff ee be stated briefly as 
follows: First. If a four affinities of an atom of carbon project 
from it toward the re ea of a regular tetrahedron, and each of 
these affinities is satisfied by a different radica , two isomers are 
possible (instead of none as predicted by the same formula con- 
e 
these radicals which cannot be made to coincide by any change of 
position. One of these stands to the other in the same — as 
that of any object to its image in a looking-glass. For example, 
one of the carbon atoms in laché acids is attached to four different 
a (CH,, COOH, H, HO), and we find two laché acids 
rdingly, one from milk, the other from flesh, resembling eac 
aha in chemical relations most closely, but differing i in physical 
are satisfied by different radicals; for instance in maleic and 
fumaric acids each carbon atom is attached to COOH and to H ; 
accounting for the ease with which its anhydride is formed ile 
in fumaric acid each carboxy] is adjacent to a hydrogen atom, 
HOOC H HOOC H 
V V/ 
© C 
Maleic acid, } Fumaric acid, ( 
Hood 1H rf Coon 
This is sagt erent a simple and probable yg ag cages of soe puz- 
zling case of isomerism, which drove Fittig in his recent classical 
n 
explained by a spiral arrangement of the different radicals 
attached to a easbunsione: ; according as this screw turns to the 
right or the left would the plane of polarization be deflected in 
_ or the other direction ; while two atoms with opposite lpi 
the same molecule would give an inactive substance. By this 
lighethoek the different forms of tartaric acid and the differences 
rs to our chemical ee and marks out a great umber “e 
new lines for experimental work.* Otte: 
anemone reat wg ee och pre Translated by 
F. Hermann as Raume. Vieweg und Sohn. 1877. 
