MICRO-CHEMICAL REAGENTS. 273 
Sachs proceeds in the following manner in the reaction for 
grape sugar. He places the (thick) longitudinal sections for 
some minutes in a solution of sulphate of copper (1 part of 
sulphate of copper and 4 parts of water), then washes them with 
water, and brings them into a boiling solution of caustic potassa 
(one part of the solution No. 8 and two parts of water). Cells 
containing grape sugar then appear filled with a reddish-yellow, 
granular precipitate (Cu,O). In this reaction it is necessary to 
accurately proportion the time that the section remains in the 
liquid, the amount of washing, thickness of the section, etc., 
for which some experience is required. 
The alkaline tartrate of copper imparts to the albuminous 
substances deposited in the parenchyma a violet color, in con- 
sequence of the formation of compounds of copper with the pro- 
tein substances, as was made known in 1872 by Ritthausen. 
12. Ammoniacal Solution of Oxide of Copper is obtained 
by shaking copper turnings with ammonia water of the specific © 
gravity 0.960, with the addition of very little ammonium 
chloride. The ammonical oxide of copper, when prepared in an- 
other manner, has a different action in some cases. This liquid 
is the only solvent for cellulose. It is to be observed, however, 
that its action upon the cell-walls is very different, according to 
their thickness and purity, and that many, as for instance the 
hyphe of fungi and cork, are not attacked by it at all, or at least 
not without previous boiling with caustic alkali or with potas- 
sium chlorate and hydrochloric acid. The action of the ammoni- 
acal oxide of copper does not occur immediately. 
The ammoniacal oxide of copper is only fit for use when it dis- 
solves cotton in the course of a few hours, It is expedient to 
protect it from the action of light, and not to keep it for a very 
long time. 
13. Glycerin of the specific gravity 1. 225 is of very general 
use as a clearing agent; with a higher degree of concentration — 
its power of abstracting water also comesinto consideration. In 
the examination of such constituent substances as would dis- 
solve quickly in water (aleurone, tannic acid), concentrated 
glycerin is — useful, since its solvent power is ae gradually © 
