BULLETIN OF THE BUSSEY INSTITUTION. 13 
No. 2.— Testing for Mannose. By F. H. Srorger, Pro- 
fessor of Agricultural Chemistry. 
Ir is commonly stated in the text-books * that, thanks to the 
sparing solubility of mannose-hydrazone in water, mannose may 
be detected readily, and even be determined quantitatively, by 
adding phenylhydrazin to its aqueous solution. In like manner, 
it is said that mannan may easily be detected and determined by 
boiling in a dilute acid the substances which contain it and 
adding phenylhydrazin to the liquid, after the acidity has been 
' neutralized. 
These statements are true enough in respect to the detection of 
mannose in solutions of this substance that are neither too dilute 
nor too much contaminated with impurities such as may result 
from the solvent action of water and acids on vegetable matters. 
They are true, also, in some part, in respect to substances that 
contain a sufficiently large proportion of mannan to. override 
obscurations which impurities and other complications might 
induce. It is easy, for example, to detect mannose in solutions 
prepared by oxidizing mannite, and in those obtained by hydro- 
lyzing date stones, vegetable ivory, or the wood of various conif- 
erous trees. But to detect mannan in cases where but little of it 
is present, or, still worse, to prove that it is absent in any given 
instance, is a much more difficult task, as, for example, when the 
wood of deciduous trees is tested. 
In the hope of gaining a proper mastery of the subject, I have 
had a very large number of tests for mannose made under my 
eye during the last few years, and have become so familiar with 
the difficulties which stand in the way of proving the absence of 
this substance that some part of the accumulated experience 
seems worthy of being put upon record. 
In testing substances that contain an abundance of mannan, 
the presence of this substance may be demonstrated readily 
enough by boiling some of the powdered wood or other material 
together with ten or twelve times as much hydrochloric acid of 
five per cent. over a free flame during several hours in a flask 
* Cf. Tollens, Handbuch der Kohlenhydrate, 2. 113; Maquenne, Les 
Sucres, Paris, 1900, p. 560. 
