A Manual of the Chemistry of the Carbon Compounds

TJRE CARBON COMPOUNDS. 289
of water in cauliflower-like masses, and from hot alcohol in warty,
anhydrous needles. It is less sweet than cane-sugar, and less soluble
in water, requiring about one part of cold water for solution.
. Dextrose precipitates from solutions of silver salts the metal, which,
if the solution contains free ammonia, separates in form of a brilliant
minor on the sides of the vessel "When it is heated with an alkaline
solution of a cuprio salt, red cuprous oxide is precipitated. This
reaction is made use of for the quantitative determination of grapesugar.
A. standard solution (Fehling's solution) is prepared by
dissolving 34-64 grammes of crystallized copper sulphate and 200
grammes of Kochelle salt in 600 to 700 ob. cm. of soda-solution (specific
gravity 1'2), and diluting with water up to exactly one litre. As one
molecule of grape-sugar reduces exactly five molecules of the copper
salt, oneob. cm. of the solution corresponds to 0*005 gramme of grapesugar.
The analysis is performed as follows:—10 cb. cm. of the.
standard solution are placed into a basin, and after being diluted
with some water the liquid is heated to the boiling-point, and then
the sugar solution added by means of a burette until the blue colour
has completely disappeared.
Another simple method is founded on the fact that grape-sugar
reduces an alkaline solution of meronrio cyanide to metallic
mercury. 10 grammes of pure mercuric cyauide are dissolved in water,
100 cb.cm. of soda-solution (1145 specific gravity) are added,and the
whole diluted with water to one litre, 40 cb. cm. of this solution
correspond to 0*1 gramme of sugar. The analysis is performed in the
same way as in Fehling's method, and the end of the reaction recognized
by bringing a drop of the solution on Swedish filter-paper, and
holding it over strong ammonium sulphide, a brown stain being
produced as long as any mercuric cyauide remains in solution.
Dextrose melts at 170°, losing water at the same time, and being
converted into gltuosau C8Hi0O(,a colourless mass, which is scarcely
sweet to the taste, and which by boiling with a dilute mineral acid is
reconverted into dextrose. When dextrose is more strongly heated, it
yields the same products as cane-sugar.
Concentrated sulphurio acid dissolves dextrose without blackening,
iextrosesulphwio acid being formed, the barium salt of which is
soluble in water.
Nitrio acid oxidizes it to saccharic acid, and by acting on it with
chlorine and moist silver oxide glvamio acid (page 287) is formed.
By the action of boiling acetic anhydride the diacetate
C 8H«O0(CaH8O)2 is obtained as a colourless mass, having a bitter taste;
at the same time also the triacetate C0H9Oa(OjagO)3 is formed, a
similar body which is less soluble in water than the diacetate,
The compounds of dextrose with bases are very unstable bodice.
By saturating its solution with lime, a strongly alkaline solution is
obtained, which when kept for some time becomes neutral, and contains
then the calcium salt of glwinic acid OuHjgOj; the free acid
is a sour, deliquescent, amorphous mass.
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