PHYSIOLOGICAL CHEMISTRY 277 



is often of value. For this purpose the crystals of osazone are collected on a 

 filter paper, washed with water acidulated with acetic acid, recrystallised from 

 water, alcohol or acetic acid, and dried by placing in a desiccator over H 2 S0 4 . 

 They are then placed in a narrow glass tube closed at one end and tied on to 

 the bulb of a thermometer by a fine platinum wire. The thermometer is 

 suspended in a long necked Jena flask in which is concentrated H 2 S0 4 (almost 

 saturated with K^SC^ to prevent fuming) and the temperature gradually raised 

 by heating the flask over wire gauze. The bulb of the thermometer should dip 

 into the sulphuric acid. The exact temperature at which the crystals begin 

 to melt and the temperature of complete fusion are noted. For accurate work, 

 a correction is necessary because the mercury thread is cooler than the bulb of 

 the thermometer. 1 and 2 



The following are the melting points of some of the most important osazones : 

 Dextrosazone, 3 - - - - 204-205 C. 



Lactosazone, .... 200 C. (Begins to melt at this temp.) 

 Maltosazone, .... 206 C. 



If the crystals are pure, melting occurs at once, but if they are impure 

 there may be a considerable difference in temperature between the points of 

 commencing and complete fusion. 



If an osazone be hydrolysed by treating with fuming HC1 it breaks up, 

 phenyl-hydrazine being set free, and a body called an osone resulting. This 

 latter has the formula CH 2 OH - (CHOH) 3 - CO - CHO, from which it is seen that 

 it contains both an aldehyde and a ketone group. The former of these groups 

 can be converted into the CH 2 OH group of sugar by treating with a reducing 

 agent, 



CH 2 OH - (CHOH) 3 - CO - CHO + H 2 = CH 2 OH - (CHOH) 3 - CO - CH 2 (OH) 

 which is the formula for laevulose (a ketose). 



The aldoses can thus be changed into the ketoses, and if the aldose obtained 

 by condensation of formaldehyde be used as the starting point an interesting 

 synthesis from a simple aldehyde to a more complex one and then to a ketose is 

 illustrated. It is believed by some that formaldehyde is the chemical substance 

 which, by a process of reduction, chlorophyll-containing plants first form 

 from C0 2 and H 2 0. By condensation of several (five or six) formaldehyde 

 molecules pentoses or hexoses become formed, and from these the more 

 complex carbohydrates. By other chemical actions fats and proteins can then 

 be produced. 



///. The simple sugars can be artificially prepared by careful oxidation of 



1 To make the above correction, a second thermometer must be suspended in the 

 flask with its bulb opposite the middle of the column of mercury of the main 

 thermometer, the formula for correction is then ^(^-^(0 '000154) where L = the 

 height of the mercury column of the main thermometer above the sulphuric acid 

 measured in degrees; T 7 the reading of the main thermometer; t the reading 

 of the air thermometer. This correction must be added to the reading T of the 

 main thermometer. 



2 Too much reliance must not be placed on a determination of the melting points 

 of osazones in identifying unknown sugars, for they vary with the rate of heating 

 and with the method of purification of the osazone. 



3 Laevulose forms the same osazone as dextrose. 



