98 THE ROYAL SOCIETY OF CANADA 



ovens; but an oven of large cross section on account of the slow trans- 

 mission of heat through the charge, either involves a long heating period, 

 which is expensive, or a big difference in final temperature between 

 the outside and the inside layers of the charge. These difficulties 

 may be overcome with non-coking coals by the use of inclined rotary 

 ovens, the charge being thus kept stirred and uniformly heated; but 

 such ovens have not yet become commercially established. 



The regular and the slow series of tests were carried out to show 

 what difference, if any, was caused by the rate of heating, and also 

 what effect the final temperature had on the result — information 

 which the above discussion shows to be essential for the correct 

 design and operation of a lignite retort. The results so far obtained 

 indicate little difference between rapid and slow heating, and point 

 to nearly 600°C., as the most satisfactory temperature. They also 

 show that if, in order to raise the centre of the charge to 600°C., the 

 walls of the retort are heated to a higher temperature, a falling off 

 in calorific value results. On the other hand, if the walls of the retort 

 are heated to 600°C., the results can be employed to estimate both the 

 higher volatile matter content, and the lower calorific value, to be 

 expected in the successive layers approaching the centre of the charge, 

 when the temperature gradient is known. Definite conclusions 

 cannot, however, be drawn from these experiments, until information 

 is also available with regard to the value of the by-products obtained 

 under any given conditions. 



An investigation begun by Pictet & Bouvier of Geneva in 1913, 

 showed that the tar produced by distilling coal at a low temperature 

 and pressure was markedly different from normal coal tar. The 

 writers are not aware that any commercial advantage has yet been 

 taken of this discovery, but it seemed important, nevertheless, to 

 investigate the effect of low pressure in the carbonization of lignite. 

 The results obtained in the vacuum series indicate that the temperature 

 necessary for satisfactory carbonization cannot be notably decreased 

 by the use of low pressure. More notable results are to be expected 

 when the yield and nature of the by-products are also studied. 



Serious trouble is experienced in the commercial carbonization 

 of lignite on account of the great inflammability of the hot resi- 

 due, and the difficulty of cooling it completely without access of air. 

 The rapid change noted in the residue?, even after cooling, has con- 

 siderable significance in connection with this trouble. It is well known 

 that when freshly prepared charcoal is first exposed in bulk to the air, 

 it is liable to catch fire spontaneously, even if originally cold, owing 

 to the heat generated by the occlusion of air; and the behaviour of 

 carbonized lignite appears to be closely comparable. It is^easy to 



