30 BULLETIN OF THE BUSSEY INSTITUTION. 
Details of the Method of applying the Phenylhydrazin Test 
for Mannose. 
In the actual testing of woods for mannan, a convenient method 
of procedure is to boil about 20 grm. of the finely powdered wood, 
regarded as dried at 100°C., in 200 cc. of hydrochloric acid of 
5. per cent. during three hours, over a free flame, to neutralize the 
filtered product of the hydrolysis with dilute caustic soda (1: 8) 
and to test 1 cc. portions of the unevaporated filtrate by adding 
twelve drops of the phenylhydrazin reagent. In case much man- 
nose is present, it is a matter of indifference whether the reagent 
used has been prepared by mixing phenylhydrazin and acetic acid, 
as has been explained above on page 14, or by mixing pheny]l- 
hydrazin hydrochlorate and sodium acetate; but when any uncer- 
tainty exists as to the quantity of mannose to be expected, it is 
well to make two separate tests, — one with each of the reagents. 
On the whole, the mixture of phenylhydrazin and acetic acid gives 
rather better results than the hydrochlorate and sodium acetate, 
though the latter sometimes yields cleaner and clearer crystals of 
mannose-hydrazone, since the confusing, spiny crystals of dex- 
trose-osazone are apt to form somewhat sooner in the acetic 
solution than in the other. Experience has taught that, when 
operating on the unevaporated liquor, it is best to add as much 
as twelve drops of the reagent rather than a smaller number. 
After the addition of the reagent the mixture is left to stand at 
rest for a couple of hours, and is then examined with the micro- 
scope. If the result of this examination leaves nothing to be 
desired, the experiment is regarded as finished; bat if only a 
small quantity of mannose-hydrazone is visible, the mixture 
should be left to stand over night. 
If the precipitate obtained on thus testing the unevaporated 
product of the hydrolysis is seen to contain actual crystals of 
mannose-hydrazone when. examined under the microscope, no 
further steps need be taken. But if only balls appear, whether 
smooth or roughened, the supernatant liquor is poured off from 
the precipitate and the latter is washed with cold water, by way 
of decantation, to remove common salt and other extraneous 
matters, as has been explained on page 17, and the precipitate 
is dissolved in warm, somewhat diluted alcohol (3:1). On allow- 
