196 HOW TO TEST CANE JUICE. 
copper upon mere exposure to heat. This might be pre- 
vented, however, by the fresh addition of solution of 
soda. Before using the solution, boil 10 ¢. ce. of it for 
some minutes, by way of trial, with 40 c. c. of water, or 
dilute solution of soda if there is reason to believe that 
the fluid has absorbed carbonic acid; if this operation 
produces the least change in the fluid, and causes the sepa- 
ration of even the smallest quantity of suboxide, the solu- 
. tion is unfit for use. 
“The process.—Pour 10 ¢. c. of the copper solution into 
a porcelain dish, add 40 c. c. of water, or very dilute solu- 
tion of soda if required, heat to gentle ebullition, and 
allow the sugar solution to drop slowly and gradually into 
the fluid from a burette or pipette divided into j;,¢. ¢. 
After the addition of the first few drops, the liquid shows 
a greenish-brown tint, owing to the suboxide and hydrated 
suboxide suspended in the blue solution. In proportion as 
more of the sugar solution is added, the precipitate be- 
comes more copious, acquires a redder tint, and subsides 
more speedily, When the precipitate presents a deep-red 
color, remove the lamp, allow the precipitate to subside a 
little, and give to the dish an inclined position, which will 
enable you readily to detect the least bluish-green tint. To 
make quite sure, however, pour a little of the clear super- 
natant liquid into a test tube, add a drop of the sugar 
solution and apply heat. If there remains the least trace 
of salt of copper undecomposed, a yellowish-red precipitate 
will form, appearing at first like a cloud in the fluid. In 
that case pour the contents of the tube into the dish, and 
continne adding the solution of sugar until the reaction is 
complete. The original amount used of the solution of 
sugar contains 0°050 grammes of anhydrous grape sugar. 
‘‘When the operation has terminated, ascertain whether 
it has fully succeeded; that is, whether the solution really 
