504 Wisconsin Academy of Sciences, Arts , and Letters. 
saure 7 (d lactic acid) to distinguish it from ‘gahrungs milch- 
saure 7 (dl lactic). According to Want ’Hoff’s idea, the differ¬ 
ence in physical properties of optical antipodes could be indi¬ 
cated structurally in a simple manner by means of a different 
arrangement of the various groups around the asymmetric car¬ 
bon atom. 
To maintain a rational system it was necessary, of course, 
that in the simple exchange of one radical for another in an op¬ 
tically active compound by means of various reagents, no re¬ 
arrangement off the atoms in space should occur—in other 
words, the substituted product should have a structure corre¬ 
sponding to that of the original material, as is represented by 
the following scheme: 
COOH 
I 
COOH 
COOH 
HO—C —H 
| 
Cl—C—H 
| 
HO—C—H 
1 + PC1 5 — y 
| +KOH - 
—> 1 
HC—H 
| 
HCH 
HC—H 
1 
COOH 
| 
COOH 
COOH 
1 malic 
1 chlorsuccinic 
1 malic 
Walden determined that these changes took place as indi¬ 
cated, both of which according to his latest work he regarded 
as normal. 3 Tie discovered, however, that by using moist silver 
oxide to replace the halogen, he always obtained an abnormal 
result (a product which demanded a rearrangement of the 
atoms in space). Such an abnormal result always lights the 
way to a new discovery, and demands an extension or revision 
of our present theory. Walden was, therefore, not slow in an¬ 
nouncing that he had obtained an inversion in the optical ac¬ 
tivity off malic acid by means of a simple cycle in which OH 
was replaced by Cl using phosphorus pentachloride, and the 
halogen atom, in turn, was replaced by hydroxyl using moist 
silver oxide—whence the name, the ‘Walden inversion. 7 
COOH 
COOH 
COOH 
—i —h 
ClC—H 
| 
H-C-OH 
I 4-PC1 b 
—y 1 + AgCi-> 
1 
HC—H 
HCH 
H_C—H 
COOH 
| 
COOH 
| 
COOH 
1 malic 
1 chlorsuccinic 
d malic 
