BULLETIN OF THE BUSSEY INSTITUTION. 17 
hydrazin is present, no good results are to be expected. But in 
somewhat stronger solutions precipitates composed of yeast-like 
globules or of globules with stubby spines or of crystalline bundles 
composed of rhombic prisms will appear. 
It should be understood clearly that the mere formation of a 
yellowish precipitate, on adding phenylhydrazin compounds to 
products of the hydrolysis of wood or other vegetable matter, is 
of itself no evidence whatsoever of the presence of mannose in 
those liquors, for yellowish or yellow-red precipitates may be 
produced by phenylhydrazin under a great variety of circum- 
stances, —-notably in most solutions obtained by hydrolyzing 
vegetable matters, in solutions of dextrose, as has been said, and 
also when a dilute aqueous solution of tannic acid is mixed with 
phenylhydrazin acetate. Even when distilled water, phenylhydra- 
zin, and acetic acid are mixed, a slight turbidity appears at once, 
and a visible yellowish amorphous deposit will separate in the 
course of a day or two. 
Recrystallization of Mannose-hydrazone from diluted Alcohol. 
» As a preliminary to the recrystallization of the mannose-hydra- 
zone from alcohol, the liquid lying above the original precipitate 
should be removed either by decantation or by means of a small 
pipette or by absorption with little rolls of filter paper; the pre- 
cipitate should be washed with water, by decantation, to remove 
sodium chloride, etc., and finally be covered with diluted alcohol 
(three parts of alcohol of 95 per cent. and one part of water) and 
warmed on a water bath to 75 or 80°C. The alcoholic solution 
is then allowed to evaporate very slowly until crystals appear. 
In case suspicion should arise in any instance that the yeast-like 
globules of mannose-hydrazone above described might possibly be 
not mannose-hydrazone but simply small drops of free phenyl- 
hydrazin, the doubt may be dispelled readily by treating the 
washed precipitate with a little glacial acetic acid, which will 
dissolve phenylhydrazin and other matters, but not the mannose- 
hydrazone. It is to be noted that the glacial acid should be 
applied to the washed precipitate, for if it were put upon a pre- 
cipitate contaminated with sodium chloride, some of the latter 
might be precipitated in crystalline forms. Even on allowing a 
drop of glacial acetic acid to flow in upon well-washed balls 
