OBSERVATIONS ON THE DAUBREE EXPERIMENT 



13 



exposed to a pressure lower than the total pressure to which the 

 water just within the pore is subject. The latter condition would 

 appear to be equivalent to the assumption that, excepting the cases 

 where the capillary pressures are relatively large (i.e., at small 

 depths with very fine pores), the rock mass or magma in question 

 is situated in some sort of cavity, the walls of which protect it 

 from the full load due to the weight of the overlying strata. 



TABLE II 



To Indicate the Magnitude of the Pressures (in Kg. per Sq. Cm.*) Pro- 

 ducible BY Capillarity under Various Conditions; the Values Given 

 Are Approximate and Subject to the Assumptions Stated Above 



Depth 

 Meters 



Pressure 

 Outside 

 Pores Due 

 to Over- 

 lying Rock 



Temperature Gradient, 1° C. per 30 Meters 



100 



200 



500 



1,000 



2,000 



5,000 



10,000 



20,000 



50 

 100 

 200 

 300 

 400 



27 



54 

 135 

 270 



54° 

 1350 

 2700 

 5400 



Temperature Gradient, i°C. per Meter 



14 



27 



54 



81 



108 



per sq. cm. =o.g7 atm. 



From this table it is evident that the pressure producible by 

 capillarity is insignificant in comparison with the hydrostatic pres- 

 sure, except for very fine pores. For each size of pore there is 

 a definite depth above which the combined hydrostatic and capil- 

 lary pressure exceeds the rock pressure, and below which the rock 

 pressure (presuming that it is fully effective) predominates. For 

 instance, in pores of o.oi ju diameter and with the normal tem- 

 perature gradient, the depth at which the opposing pressures just 



