EXPERIMENTAL, MILLING AXD BAKING. 45 
ANALYSIS FOR REDUCING SUGARS— VOLUMETRIC THIOSULPHATE METHOD. 
Reagents: Sozhlet's Modification of F< Tiling's Solution. — Prepared by 
mixing, immediately before use, equal volumes of (a) and (b). 
(a) Copper sulphate solution. — Dissolve 34.639 grams of copper sulphate (CuS0 4 5H 2 
in water and dilute to 500 cubic centimeters. 
(6) Alkaline tartrate solution. — Dissolve 173 grams of Rocehlle salts and 50 grams of 
sodium hydroxid in water and dilute to 500" cubic centimeters. 
(c) Standard ihiosulphate solution. — Prepare a solution of sodium thiosulphate 
containing 19 grams of pure crystals in 1 liter. Weigh accurately about 0.2 gram of pure 
copper foil and place in a flask of 250 cubic centimeters capacity. Dissolve by warm- 
ing with 5 cubic centimeters of a mixture of equal volumes of strong nitric acid and 
water. Dilute to 50 cubic centimeters, boil to expel the red fumes, add 5 cubic 
centimeters of strong bromin water, and boil until the brornin is completely driven off. 
Remove from the heat and add a slight excess of strong ammonium hydroxid (aboul 7 
cubic centimeters is required). Again boil until the excess of ammonia is expelled, 
as shown by a change of color of the liquid, and a partial precipitation. Then add a 
slight excess of strong acetic acid (3 or 4 cubic centimeters of 80 per cent acid) and boil 
for a minute. Cool to room temperature and add 10 cubic centimeters of 30 per cent 
potassium iodid solution. Titrate at once with the thiosulphate solution until the 
brown tinge has become weak, then add sufficient starch indicator to produce a marked 
blue coloration. Continue the titration cautiously until the color due to free iodic 
has entirely vanished , The blue color changes toward the end to a faint lilac. If at 
this point the thiosulphate be added drop by drop and a little time allowed for com- 
plete reaction after each addition, there is no difficulty in determining the end point 
within a single drop. One cubic centimeter of the thiosulphate solution will be found 
to correspond to about 0.0005 gram of copper, 
(d) Starch indicator. — Mix about 0.5 gram of finely powdered potato starch with cold 
water to a thin paste; pour into about 100 cubic centimeters of boiling water, stirring 
constantly, and discontinue heating immediately after the paste is added. 
Determination. — Transfer 25 cubic centimeters each of the copper 
sulphate and alkaline tartrate solutions to a 400 cubic centimeter 
beaker of alkali-resistant glass and add 25 cubic centimeters of 
reducing sugar solution, or, if a smaller volume of sugar solution is 
used, add water to make the final volume 100 cubic centimeters. 
Heat the beaker upon an asbestos gauze over a Bunsen burner, regu- 
late the flame so that boiling begins in 4 minutes and continue the 
boiling for exactly 2 minutes. (It is important that these directions 
be strictly observed and, in order to regulate the burner for this pur- 
pose, it is advisable to make preliminary tests, using 50 cubic centi- 
meters of the reagent and 50 cubic centimeters of water before pro- 
ceeding with the actual determination.) Keep the beaker covered 
with a watch glass during the heating. Filter the cuprous oxid at 
once on an asbestos mat in a porcelain Gooch crucible, using suction. 
Wash thecuprous oxid thorough!}' with water at a temperatureof about 
60° C. Cover the Gooch with a watch glass and dissolve the oxid by 
means of 5 cubic centimeters of warm nitric acid (1 to 1) poured under 
the watch glass with a pipette. Catch the filtrate in a 250 cubic centi- 
meter flask, wash the watch glass and Goochfree of copper, using about 
50 cubic centimeters of water. Boil to expel redfumes, add 5 cubic 
centimeters of bromin water, boil off the bromin and proceed exactly 
as directed under "Standard thiosulphate solution." Calculate the 
milligrams of copper reduced and from Table 3 the weight of invert 
sugar equivalent to the weight of copper found. Divide the result by 
2 and multiply by 100 to obtain the percentage of sugar as invert. 
SUCROSE. 
In a 100 cubic centimeter graduated flask place 50 cubic centi- 
meters of the same filtrate, add a small piece of litmus paper, and 
neutralize with acetic acid; then add 5 cubic centimeters of concen- 
