MICRO-CHEMICAL REAGENTS. 269 
2. Hydrochloric Acid of the specific gravity 1.110 acts much 
less energetically upon the cell-walls; yet, without causing these 
to swell in a disturbing manner, it seizes upon many of the con- 
stituent substances and thereby permits the structure of the 
tissue to be more clearly recognized (a stronger acid effects 
tumefaction). Calcium oxalate (page 129) is readily dissolved 
by hydrochloric acid. 
3. Sulphurie Acid. 
The dilute acid (specific gravity 1.110) causes starch and the 
membranes to swell. Cellulose is converted by it into amyloid 
(page 159). 
Concentrated sulphuric acid (specific gravity 1.836) dissolve 
the membranes and their contents; only the cuticle, cork, 
the nucleus sheaths (page 202), intercellular substance, and the 
oil drops contained in the cell resist its action. 
In the phloroglucin reaction (page 161), sulphuric acid can be 
applied in place of hydrochloric acid. When mixed with indol ! 
the former is a good reagent for lignified membranes. 
4, Nitrie Acid of the specific gravity 1.180, either alone or 
after the addition of ammonia, colors protein substances, as also 
the middle lamella, yellow. Héhnel employs it for the detec- 
tion of suberin (cerin reaction). 
Since nitric acid dissolves starch as well as sulphuric and 
hydrochloric acids, it can likewise be employed for clearing up 
tissues which are rich in starch. 
Nitric acid alone, or, still better, a mixture of nitric acid and 
potassium chlorate (Schultze’s maceration), is the best agent for 
isolating the individual element of tissue. The boiling acid, to 
which small crystals of potassium chlorate are gradually added, 
dissolves the middle lamella. This method of procedure is par- 
ticularly applicable to the examination of vegetable powders 
(Cinnamon, Cinchona, ete.); dark membranes at the same time 
become bleached thereby. 
When treated in this manner, boiled scraps of drugs are re- 
1 A colorless crystalline principle of the composition CsH;N, ob- 
tained by the action of reducing agents on the blue coloring principle of 
indigo. F. B, P. 
