368 ON THE JUICE OP THE 8UGAR-CANE. 
or soda, the glucose becomes oxydised, and communicates a deep brown 
colour to the solution. Boiled with the tartrate cupro-potassic, it re- 
duces the metallic oxide, and gives rise to an abundant red precipitate, 
These two reactions enable us to discover traces of glucose mixed with 
cane sugar. The various terms, as sugar of fecula, of rags, of honey, of 
that found in diabetes, simply apply to glucose, the different sources of 
which they indicate. 
Uncrystallizable sugar, called also interverted sugar, sugar of 
acid fruits, levulose &c. (C 12 H 11 O 11 *) exists in most fruits, and is 
found ready formed in the stems of some plants. The action of acids 
on cane sugar will produce it in a direct manner : like glucose, it turns 
brown under the action of alkalis, and reacts energetically on the cupro- 
potassic tartrate. This uncrystallizable sugar becomes modified after a 
certain time, and is partly changed into glucose, which then appears as 
small granular crystals. For this reason, it has sometimes been con- 
sidered as a compound of glucose and liquid sugar. Taking into account 
merely certain physical characteristics of this last kind of sugar, it is be- 
yond doubt that it is not always identical in the vegetable organisation, 
and is there manifested under different molecular conditions, if not with 
a variability of its intimate composition. 
There are some other substances which have a great analogy with 
the above-named bodies both in their properties and composition; 
such as lactine, trehalose, melitose, and melezitose ; but it is sufficient 
to name these substances which, on account of their special origin, do 
not fall within the range of those mattters which are the principal ob- 
ject of these researches. 
The action which polarised light exerts on the solutions of the 
different sugars which have been passed in review, furnishes valuable 
means for distinguishing them ; and it is at the same time the surest and 
most precise method to determine their relative quantities in a liquid 
which does not contain other bodies, having equal power of reaction 
on polarised light. The modification which is communicated to polar- 
ised light by different kinds of sugars, is more or less marked, though 
not always exercised in an identical manner. Cane sugar, crystallized 
glucose, lactine, trehalose, melitose, and melezitose become on the right 
hand the plane of polarization of the light, the greatest rotatory power- 
among these substances being possessed by trehalose, and after it come 
melitose, melezitose, cane sugar, lactine and glucose. 
Diluted acids modify in an opposite sense the rotatory power of cane 
sugar which then diverts to the left the plane of polarization ; glucose, 
however does not undergo such a change under the action of acids. 
Like interverted cane sugar, the liquid sugar of acid fruits turns to 
* Gelis gives us the formula of levulose or levulozine, C 12 H 10 O 10 , that is, 
one equivalent less of water than prismatic sugar. * 
