FEHLING’S SOLUTION. 195 
filtering through boneblack as before recommended, or by 
treating about 15 c. c.* of the crude boiling juice with a 
few drops of miik of lime, filtering through animal char- 
coal, washing the precipitate thoroughly on the filter, 
adding the washings to the filtrate, and diluting it to 15 or 
20 times its original volume. Add 12 drops of dilute sul- 
phurie acid (SO, HO-+5 water) and boil the mixture from 
1 to 2 hours, adding water as it evaporates. This opera- 
tion is best conducted in a steam-bath. Neutralize the 
free acid by means of a dilute solution of carbonate of 
soda. 
The sugar solution must be highly dilute, containing 
only one-half, or, at most, 1 percent. of sugar. If in a first 
experiment the sugar solution is too concentrated, dilute it 
with a definite quantity of water and repeat the experi- 
ment. 
The copper solution prepared, as directed by Fresenius, 
gives very accurate results.f ‘‘ Dissolve exactly 34°632 
grammes of pure crystallized sulphate of copper, com- 
pletely freed from adhering moisture by pulverizing and 
pressing between sheets of blotting paper, in about 200 
ce. c. of water. Dissolve in another vessel 173 grammes of 
perfectly pure crystallized tartrate of soda and potassa in 
480 c. c. of pure solution of soda of 1 14 sp. grav. Add the 
first solution gradually to the second, and dilute the deep 
blue clear liquid exactly to 1000 c.c. Every 10c. ¢. of 
this solution contains 0°34632 grm. of sulphate of copper, 
and correspond exactly to 0-°050 grm. of anhydrous grape 
sugar. Keep the solution in a cool dark place, in well- 
stoppered bottles filled to the top, as absorption by ear- 
bonic acid would lead to the separation of suboxide of 
* ¢. c. cubic centimeters. See table V. 
{ Fresenius’s Quant. Chem. Analysis. London, 1860, pp. 576-9. 
