TEMPORARY MOUNTS AND MICROCHEMICAL TESTS 79 
of this solution added to 1 c.c. of water is good for testing. With too 
strong a solution, the starch first turns blue but rapidly becomes black. 
Grape-Sugar.—In cells containing grape-sugar, bright-red gran¬ 
ules of cuprous oxide are precipitated by Fehling’s solution. It is 
better to keep the three ingredients in separate bottles, because the 
solution does not keep long after they are mixed. The solutions 
may be labeled A, B, and C. 
^ f Cupric sulphate. 3 g. 
\ Water. 100 c.c. 
g f Sodium potassium tartrate (Rochelle salt).. 16 g. 
p f Caustic soda. 12 g. 
\ Water. 100 c.c. 
When needed for use, add to 10 c.c. of water 5 c.c. from each of 
the three solutions. The sections, which should be two or three 
cells in thickness, are warmed in the solution until little bubbles are 
formed. Too much heat must be avoided. Mount and examine in 
a few drops of the solution. The twig or organ may be treated with 
the solution, and the sections may be cut afterward. Other sub¬ 
stances precipitate copper, and may be mistaken for grape-sugar 
by the beginner. 
Cane-Sugar.—Cuprous oxide is not precipitated from Fehling’s 
solution by cane-sugar, but after continued boiling in this solution 
the cane-sugar is changed to invert-sugar and the copper is precipi¬ 
tated. The solution becomes blue. 
Proteids.—The proteids turn yellow or brown with the iodine 
solution. It is better to use a stronger solution than when testing 
for starch. It must be remembered that many other substances 
also turn brown when treated with iodine. 
When proteids are warmed gently in concentrated nitric acid, 
the acid becomes yellow. The color may be deepened by the addi¬ 
tion of a little ammonia or caustic potash. 
When proteids are heated with Millon’s reagent, the solution 
becomes brick-red or rose-red. This reaction takes place slowly 
even in the cold. The following is one formula for this reagent: 
Mercury./. 1 c.c. 
Concentrated nitric acid. 9 c.c. 
Water. 10 c.c. 
Dissolve the mercury in the nitric acid and add the water. 
