R72 MICRO-CHEMICAL REAGENTS. 
preferable to potassa and soda, since the two latter frequently pro- 
duce an altogether too energetic swelling, which detracts from 
the clearness of the outlines. The jelly which is formed by the 
action of the alkalies upon starch also interferes very much. 
By the application of ammonia neither of these objectionable 
results are produced, while its power of dissolving coloring sub- 
stances is not less in extent. Starch suffers no change by the 
action of ammonia. 
Ammonia water, still further diluted, is adapted for softening 
dried plants and many drugs which it is desired to examine 
more thoroughly. Sections which are treated with nitric acid, 
and afterward washed and moistened with ammonia, admit of 
the sharp recognition of protein substances and of the middle 
lamella by means of their yellow color (xantho-protein reaction). 
11. Alkaline Solution of Tartrate of Copper. The solu- 
tion of the tartrate of copper and sodium in caustic alkali, the 
so-called ‘‘ Fehling’s solution,” is not convenient for micro- 
chemical purposes. In place of it, the following method of 
procedure may be recommended: A solution of 3 parts of 
sulphate of copper (blue vitriol), free from iron, in 30 parts of 
hot water is mixed with a solution of 7 parts of Rochelle salt 
(potassio-sodium tartrate) in 20 parts of hot water, the resulting 
precipitate collected and dried. When used, alittle of this pre- 
cipitate is brought upon the object-glass, a small fragment of 
caustic soda added, and thereupon a few drops of water until a 
clear solution is produced, or this may also be effected by the use 
of the least possibly quantity of the solution of caustic alkali (No. 
8). The section is then moistened therewith. This alkaline 
solution of the tartrate of copper is useful in testing for sugar, 
since uncrystallizable, so-called fruit sugar (page 142) imme- 
diately separates therefrom reddish-yellow, hydrated cuprous 
oxide. This also occurs very soon by theaid of a gentle heat 
when grape sugar is present, but not even by boiling in the case 
of cane sugar (or mannite). Dextrin is also capable of reduc- 
, _ ing the tartrate of copper with the aid of heat. 
The varieties of gum and mucilage effect no reduction in the 
es alkaline solution of tartrate of copper. 
