( 269 ) 
was that the two substances behave erystallographically and optically 
in exactly the same way. 
At that time we still hesitated, however, to assume that w-tagatose 
was /-sorbinose; on reduction some /-dulcite was always obtained 
along with J/-sorbite and /-idite. The specific rotatory power of 
w-tagatose to the right remained, even after repeated crystallisations 
from water, methyl- and ethylaleohols, about 4° less than that of 
d-sorbinose to the left; the crystals were never quite clear but 
always slightly turbid. 
After many attempts to convert w-tagatose into a crystalline 
compound from which the pure ketose could be regenerated, we 
attained our object by the employment of aniline. It was then 
found that d-tagatose crystallises together with w-tagatose in a 
very persistent way, but forms an anilide much more readily than 
its isomer so that the latter is deposited in well formed, clear erystais 
from an alcoholic solution containing aniline. The w-tagatose purified 
in this way was then proved with certainty,to be the optical opposite 
of d-sorbinose and it is therefore henceforth to be regarded as 
l-sorbinose. A short summary of the comparative experiments which 
place this view beyond doubt follows. 
The melting points are the same (about 154°); from a mixture 
of equal quantities of the two ketoses a well crystallised racemic 
compound is obtained with approximately the same melting point 
and a somewhat higher specific gravity. 
The specific gravities and the solubilities in water and methyl- and 
ethylalcohols are the same. 
For d-sorbinose, am = — 42°.7, for /-sorbinose am, = + 42°.3 
(4 percent solutions at 17°). Both solutions show the same slight 
birotation. 
It has already been remarked that the two ketoses are erystallo- 
graphically identical; hemihedral faces will be again sought for. 
The osazones have the same melting point (150 to 151°), the 
same solubility and equal and opposite rotatory powers. 
l-Sorbinosazone is, as a comparison shows, identical with 
l-gulosazone. ') 
On reduction with sodium amalgam, d-sorbite and d-idite are 
formed from d-sorbinose, /-sorbite and /-idite from /-sorbinose; these 
1) The statement in von LIPPMANN's „Chemie der Zuckerarten”, p. 534, that sorbin- 
osazone is not identical with gulosazone is, according to a communication from the 
author, a mistake, 
