FEHLING’S SOLUTION. 197 
contains neither copper, sugar, nor a brown product of the 
decomposition of the latter. To this end filter off a por- 
tion of the fluid while still quite hot. The filtrate must be 
colorless (without the least brownish tinge). Heat a por- 
tion of it with a drop of the copper solution, acidify two 
other portions, and test the one with ferrocyanide of po- 
tassium, the other with sulphuretted hydrogen. Neither 
of these tests must produce the slightest alteration. If 
the fluid contains a perceptible quantity of either oxide of 
copper or sugar, this is a proof that too much or too little 
of the latter has been added, and the experiment must 
accordingly be repeated. The results are constant and 
very satisfactory. Bear in mind that the solution of sul- 
phate of copper must always remain strongly alkaline; 
should the sugar solution be acid, some more solution of 
soda must be added.” 
Second method.—This may be resorted to in cases in 
which from the dark color of the saccharine fluid it is diffi- 
cult to determine the exact point at which the process of 
reduction and separation is accomplished. In this case 
the solution of copper may be used in excess, and the sub- 
oxide which precipitates determined. 
“This requires the same solutions as the first. Pour 20 
e. c. of the solution of copper and 80 c. ce. of water, or of 
highly dilute solution of soda, if required (or a larger quan- 
tity of the copper solution diluted with water, or solution 
of soda in the same proportion), into a porcelain dish. 
Add a measured quantity of the dilute sugar solution, but 
not sufficient to reduce the whole of the oxide of copper, 
and heat for about 10 minutes on the water-bath. When 
the reaction is completed, wash the precipitated suboxide of 
copper by decantation with boiling water. Pass the decanted 
fluid through a weighed filter, dried at 212° F., then trans- 
fer the precipitate also to the filter, dry at 212° F., and 
17* 
