386 Mangham— Observations on the Osazone Method 
the concentration of the solution and was approximately constant for any 
given dilution. 
Similar results were obtained with levulose, which, however, always 
gave a precipitate in about one-third of the time required by the same 
amount of dextrose. 
Invert sugar yielded the osazone almost as rapidly as levulose of the 
same concentration. 
The rate of precipitation was accelerated by the addition of certain 
other sugars. For example, the time required for precipitating the osazone 
from a solution containing o-i per cent, of dextrose was shortened con¬ 
siderably in the presence of 5 per cent, raffinose, a sugar giving no direct 
reaction itself. 
Cane sugar was found to produce a similar acceleration with levulose 
solutions. 
On the other hand, maltose, and to a greater extent lactose, retarded 
the precipitation and interfered much more seriously in the case of dextrose 
than in the case of levulose. 
These results obtained in aqueous solutions have not been compared 
fully with those given in glycerine solutions. But some of the earlier 
experiments carried out by the author before becoming acquainted with the 
above work showed that mixtures of dextrose and maltose gave the reaction 
less readily than mixtures of levulose and maltose, and that in a mixture of 
dextrose and levulose the reaction did not appear to be at all hindered. 1 
Moreover, in the case of the levulose and maltose mixture typical levulose 
osazone crystals were found on examining immediately after the heating, 
whereas no crystals could be seen in the dextrose and maltose mixture 
until about two hours later, and then small ones slowly formed. A similar 
dextrose solution alone gave large crystals immediately on cooling. In 
these experiments the preparations were heated for half an hour. 
As the behaviour of dextrose and levulose in glycerine is on the whole 
much the same as in water, there is little reason for doubting that the 
results obtained in aqueous solutions would apply also when the reaction is 
carried out with Senft’s reagent, although the effect would be intensified 
owing to the viscosity of the glycerine. 
Here then is another reason for allowing due time to elapse before 
drawing conclusions from the application of the reagent to plant tissues 
known to form starch and thus likely to contain maltose and dextrose. 
Various points in connexion with the use of Senft’s reagent in botanical 
work have now been dealt with, but one or two more call for remarks. 
Oxidation . The formation of brown substances in presence of air, and 
more rapidly when water is present too, has been referred to above. This 
1 These experiments were only roughly quantitative, as drops of 5 per cent, aqueous solutions 
were added to Senft’s reagent in approximately equal amounts in the various cases. 
