680 PHARMACEUTICAL BOTANY 
Rotary MicroroMe.—When paraffin ribbons are desired, 
especially for the study of serial sections of material, the rotary 
microtome surpasses by far the efficiency of the sliding type of 
instrument. The Spencer Rotary Microtome No. 820 is shown 
in Fig. 507. 
REAGENTS AND STAINS AND METHODS OF PREPARATION 
OF MATERIALS 
The following reagents will be found of value in the micro- 
scopical examination of plants, powdered vegetable drugs and 
foods: (additional reagents and formulas for their preparation 
are presented elsewhere in the text in connection pith methods 
of examination). 
Acetic Acip.—This reagent should contain not less than 
36 per cent. nor more than 37 per cent. of pure acetic acid. It is 
used for various operations such as distinguishing between cal- 
cium carbonate which dissolves in it with effervescence and 
calcium oxalate which is insoluble in it. A 2 to 3 per cent. 
solution is occasionally employed as a mounting medium for 
microscopic plants. 
Acip ALCOHOL.—Mix 149 cc. hydrochloric acid with 100 cc. 
of 70 per cent. alcohol. This is employed in removing the excess 
of stain from overstained material. When used, it should be 
thoroughly. washed out with diluted alcohol or water. 
ALCOHOL.—Useful in the form of various percentage solu- 
tions for dehydrating, preserving, hardening and solvent pur- 
poses. Absolute alcohol (Dehydrated alcohol) should contain 
not less than 99 per cent. by weight of ethyl hydroxide and must 
be kept in well stoppered bottles because of its property of rapidly 
absorbing moisture from the air and so becoming reduced 
in strength. It should always be used before cedar oil or xylol 
in making a balsam mount, but if clove oil is used for clear- 
ing instead of cedar oil or xylol, 95 per cent. alcohol may be 
employed. 
ALCANNA TINCTURE.—Macerate 20 Gm. of alkanet root for a 
week in 100 cc. of 90 per cent. alcohol, boil for several minutes 
and cool. Dilute with an equal volume of water just before 
SST ae On eee Te Oe 
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