84 



3JE. W. E. BALDWIN-WISEMAN ON 



[Feb. 1907 



extremely slow ; but, when there is an increase in the velocity of 

 the air-current, or in the temperature of the surrounding air, 

 desiccation proceeds at a greater rate. Thus, for instance, in 

 experiments recorded in another paper (24), the quantity of inter- 

 stitial water evaporated in 165*9 hours when the temperature was 

 8° or 9° C. was only 032 of that evaporated in 5 - 7 hours when the 

 temperature was 95° C. ; and, for the same degree of initial 

 saturation, the ratio would have been much less than 0*32. 



Most of the water was expelled from the pores during the first 

 few hours' exposure ; for, when stones were continuously exposed to 

 a temperature of 98° C. in a steam-oven for a period of 6 days, there 

 was little or no appreciable difference of weight when cooled, between 

 the weight at the end of each consecutive 12-hour period and that 

 at the end of the first 6-hour period. 



I also found that most of the moisture was expelled at this 

 temperature ; for, upon subsequently exposing some test-pieces, 

 which had been previously dried, for a period of 1 hour to a tempe- 

 rature of 98° C. in the steam-oven, and thereafter for a period of 

 2 hours to a temperature of 300° C. in the electric furnace, I found 

 that the decrease of weight, as shown in the following Table (II), did 

 not affect the resultant capacity for contained water by more than 

 0-5 per cent. 



Table II, showing the Effect of Drying Stones in a Steam-Oven for 1 hour 

 at 98° C. and in an Electric Eurnace for 2 hours at 300° C. 



Variety of 

 stone. 



Volume 



in 



cub. cms. 



Weight in grammes, 

 after drying in 



Difference of 

 weight 



Steam- 

 oven. 



1 



Electric 

 furnace. 



in 

 grammes. 



0-20 



o-oi 



0-25 

 001 



0-05 



o-oo 



as a 

 percent. \ 

 of the ,' 

 volume, i 



: York 



62-8 

 69-4 

 58-4 

 58-3 

 49-2 

 34-9 



135-73 

 13953 

 12735 



127-08 

 98-80 

 61-30 



135-53 

 139-52 

 127-10 

 127 07 



98-75 

 61-30 



0318 





0014 | 



Red Mansfield 



0-428 



Portland Base-bed ... 

 Monks Park 



0-017 

 0102 I 



Bradford Oolite 



o-ooo 



1 



In all cases recorded in this paper, the porosity is calculated from 

 the difference in weight of several specimens of the particular stone 

 after prolonged soaking under a hydrostatic pressure of about 40 lbs. 

 per square inch, and the respective weights of the same specimens 

 when dried in the steam-oven until there was no further diminution 

 of weight : the specimens not being weighed until they had cooled 

 to about 10° C 



