Temporary Mounts and Microchemical Tests 75 



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. 



{ Cupric sulphate 3 g. 



\ Water 100 c.c. 



J Sodium potassium tartrate (Rochelle salt).. . . 16 g. 



' \ Water 100 c.c. 



( 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 may 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 taked 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. 



