60 BULLETIN OF THE BUSSEY INSTITUTION. 
the beginning of the evaporation. Practically, it was found that 
the residues left after the evaporations exhibited an acid reaction 
on being taken up with water. 
The following experiments were made for the purpose of study- 
ing the amount of influence which may be exerted by the presence 
of asmall quantity of alkali in a dextrose solution, and of learning 
whether in actual practice there is any probability that the accuracy 
of the test for mannose might be impaired in case the neutralization 
of the products of the hydrolyses were to be pushed too far. 
Tests, based on Lobry de Bruyn’s* original experiment, were 
made as follows: One gram of pure dextrose (from Merck & Co.) 
was dissolved in a very small quantity of water and 1.4 grm. of 
potassium hydroxide were dissolved in 25 cc. of water. To the 
dextrose solution 5 ce. of this normal potash solution were added 
and the resultant mixture, amounting to 10 cc., was divided into 
two equal portions, each of which contained 2.5 ec. of the normal 
potash solution, 7. ¢., 0.14 grm. of KOH. One of these portions 
was heated on a water-bath for an hour and a half at a tempera- 
ture of 70° C. and was then nearly but not quite neutralized with 
hydrochloric acid of 5 per cent. The slightly alkaline liquid was 
evaported at a temperature of 70° to soft dryness, and the residue 
was taken up with 1 cc. of water. To this solution 20 drops of 
the phenylhydrazin acetate reagent were added. A brown pre- 
cipitate that contained much amorphous matter formed at once. 
After it had stood for two hours mannose-hydrazone balls were 
seen in it with the microscope, and on recrystallizing from warm 
diluted alcohol (three parts of aleohol of 95 percent. and one 
part of water) good crystals and plates of mannose-hydrazone 
were obtained. The other portion of mixed dextrose and potash 
was heated for an hour and a half on a boiling water-bath, then 
nearly neutralized with hydrochloric acid of 5 percent. and evap- 
orated to soft dryness on the water-bath. The residue was taken 
up with 1 cc. of water and the solution mixed with 20 drops of 
the phenylhydrazin acetate reagent, but a far less satisfactory 
result than that of the foregoing experiment was obtained. Only 
a few globules, somewhat resembling mannose-hydrazone balls, 
appeared in the amorphous precipitate, and no crystals were got 
on trying to recrystallize the balls. 
* Recueil des Travaux Chimiques des Pays Bas, 1895, 14. 158-161, 204. 
