This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
The purity of cane-sugar is ascertained by the physical properties described above, and by its complete solubility in water and alcohol. The absence of glucose or of a similar sugar is ascertained by some of the reactions given below.
"Aqueous and alcoholic solutions of sugar should have no effect on litmus paper. The solution in 20 parts of distilled water should be scarcely rendered turbid by silver nitrate or barium nitrate (chloride and sulphate)". - P. G. "Neither an aqueous nor an alcoholic solution of sugar kept in large, well-closed, and completely filled bottles should deposit a sediment on prolonged standing (absence of insoluble salts, foreign matters, ultramarine, Prussian blue, etc.). If a portion of about 1 gramme of sugar be dissolved in 10 ccm. of boiling water, then mixed with 4 or 5 drops of test solution of nitrate of silver (one part dissolved in 19 parts of distilled water), and about 2 ccm. of water of ammonia, and quickly heated until the liquid begins to boil, not more than a slight coloration., but no black precipitate, should appear in the liquid after standing at rest for 5 minutes (absence of grape-sugar and of more than a slight amount of inverted sugar). - U. S.
1. Heat with carbonate of sodium, dissolve in water, and add a solution of nitro-prusside of sodium; blood-red color when sulphur is present. (Bailey and Schoenn.) 2. Mix with a solution of potassa, add a few drops nitro-benzol and alcohol. Reddish to red color. (Brunner.)
A solution of cane-sugar, heated with 3 or 4 per cent, of potassa for a minute or two remains colorless; glucose and milk-sugar are colored brown.
A solution of cane-sugar, mixed with a little sulphate of copper and an excess of potassa or soda, retains its blue color on boiling, but turns bright red in the presence of glucose or milk-sugar, red cuprous oxide being deposited. Glucose and most allied sugars effect the same reduction, though more slowly, in the cold.
Fehling's test is a modification of the preceding, and may be used for the quantitative determination of glucose. The test liquid is prepared by dissolving 34.64 gm. of crystallized sulphate of copper in water, adding 200 grammes of Rochelle salt, and 600 or 700 gm. of soda solution, specific gravity 1.20, and diluting the whole to 1 liter (Schorlemmer). 10 cm. of this solution are reduced by 0.5 gm. of grape-sugar. Boedecker introduced Rochelle salt in place of potassium tartrate, which was used by Fehling. The test is usually made with a solution containing about 1 per cent, of glucose; weaker solutions reduce a somewhat smaller amount of the test liquid.
The inverting action of the fruit-acids - citric and tartaric - employed in manufacturing carbonated beverages is one of the bottler's difficulties. It may under certain circumstances even destroy the flavor and spoil the goods. We shall pay close attention to this metamorphose later on under the "Prepar. ation of Syrups" and "Contamination and Ropiness of Carbonated Beverages".
Bile in the presence of sugar (of other carbohydrates and of proteids) acquires a blood-red color with concentrated sulphuric or phosphoric acid.
A little subnitrate of bismuth, boiled with solution of glucose rendered alkaline by sodium carbonate, acquires a gray or black color; pure cane-sugar produces no alteration.
Acetate of lead, added to a saccharine liquid, is precipitated white by excess of ammonia; on heating the mixture it remains unchanged if cane-sugar or milk-sugar is present, but turns orange-red with glucose.
18 gm. mercuric iodine, 25 gm. potassium iodine, and 80 gm. caustic potassa, are dissolved in distilled water sufficient to make 1 liter. 40 cm. of this solution heated to boiling are decomposed by 1.1342 gm. of glucose so that a drop of the liquid is not rendered black by sulphydrate of ammonium.
On heating a solution of glucose with a few drops of solution of silver nitrate, the liquid acquires a brown color.
An ammoniacal solution of silver nitrate containing caustic soda is reduced by glucose, with the production of a metallic mirror.
A solution of sugar heated with neutral ammonium molybdate to 100° C. (212° F.) becomes blue in the presence of glucose.