102 THE ROYAL SOCIETY OF CANADA 



The desiccators employed were 22 cm. in diameter by 16 cm. in 

 depth, sulphuric acid and a small dish of soda lime being used as 

 drying and absorbent agents. Care was taken to avoid any mech- 

 anical splashing of the acid. The weighings after drying were made 

 as soon as the dishes had cooled and as quickly as possible. 



In certain preliminary work it was observed that drying in the 

 vacuum oven at 100°C. for 5 hours invariably gave a higher result, 

 i.e., higher moisture content, than drying at 100°C. to constant 

 weight in either of the air ovens. This, it was suggested, might be 

 due to a certain absorption of oxygen by the flour as the drying of the 

 sample approached completion, the rate of oxidation or absorption 

 being higher in the air ovens than in the vacuum oven. If such were 

 the case, the percentage of loss as resulting from the use of the air 

 ovens would be less than that obtained in the vacuum oven. This 

 view received support from the plotting of time-moisture curves for 

 the electric air oven, plotting the percentage of loss in weight of the 

 flour against time of drying. The form of certain of the resulting 

 curves showed a rising to and then a slight falling away from a maxi- 

 mum point — the latter indicating an increase in weight due presum- 

 ably to absorption of oxygen. 



In the endeavour to obtain further evidence in this connection it 

 was discovered that using the electric air oven the temperature 

 at different points on the same shelf might differ by as much as 10°C., 

 the thermometer at the centre of the shelf indicating 100°C. In 

 accordance with this finding, flours dried in a position nearest the back 

 of the oven (the hottest part) showed a greater percentage of loss than 

 samples of the same flour dried nearer the door of the oven. Since 

 to plot sufficient results to produce a time-moisture curve at least 

 eight dishes in each set would be required, weighing two dishes say 

 every two hours, it was concluded that the use of this oven in the 

 manner it had been employed in obtaining the first time-moisture 

 curve could not give reliable results towards establishing the absorption 

 or non-absorption of oxygen in the drying process. 



The following modification was then employed: Samples of 

 flour were dried both in the electric air oven and the water oven, 

 taken out at intervals of two hours and replaced in approximately 

 the same part of the oven, and this repeated a number of times. 

 By this method results were obtained which showed a steady increase 

 with time in the percentage of i^oisture driven off until there was 

 no further loss of weight. Thus evidence of a satisfactory though 

 of indirect character was obtained against the view that oxygen is 

 absorbed by the flour when dried at 100°C. 



