DISCUSSION OF RESULTS 605 



vidual observer may fix on. First and most important, in our opinion, is 

 the fact that the nitrogen found in the emanation is free from argon. It 

 is plain that if atmospheric water is to reach a hot lava column at a tem- 

 perature of 1,000° or higher it must do so as a gas, and therefore on the 

 same terms as other atmospheric gases. Argon is invariably contained in 

 the air in measurable quantity and forms no chemical compounds. Whence 

 it follows that if the gases of the atmosphere had reached the liquid lava 

 in any manner whatsoever the argon would be released with the others, 

 but no trace of argon was found. 



The second difficulty is to conceive a mechanism whereby atmospheric 

 or surface water of whatever origin (for example, the sea) can make its 

 way into a lava column or basin at a temperature of 1,000° or more. The 

 Daubree experiment, whereby water vapor was found to make its way 

 through 2 centimeters of sandstone against an excess pressure within, 

 though often quoted in this connection, does not help us to a solution of 

 it. The force which was active in Daubree's experiment is the surface 

 tension of water only, 25 and water will obviously have no surface tension 

 above its critical temperature of 374° (except perhaps in so far as salts in 

 solution may have the effect of raising this critical temperature slightly) . 

 This temperature passed, water must make its way precisely like any 



25 "Capillary forces are effective only when there is a surface of separation within the 

 pores. . . . Since the pressure discontinuity occurs only at the surface of separation, 

 a column of liquid can be supported only when there is a free liquid surface within the 

 capillary. . . . 



". . . As regards the influence of temperature on the surface tension of water, all 

 the investigations unite in showing that its surface tension decreases regularly with rise 

 of temperature, becoming zero, of course, at the critical temperature where there is no 

 surface of separation. The relation is practically linear when the whole range is con- 

 sidered ; it may be represented with sufficient accuracy by the formula, 



_ a t =78 — 0.21 * or 0.21 (370 — *) 



where c t Is the surface tension at t° (temperature centigrade) expressed in dynes per 

 centimeter. 



". . . Prom this . . . it is evident that the pressure producible by capillarity is 

 insignificant in comparison with the hydrostatic pressure, except for very fine pores 

 . . . and this minuteness of the pores leads us to Inquire what amount of water could 

 actually flow through them. . . . Assuming the mean viscosity of the water to bo 

 0.005 (Its value at a temperature of 30°), the amount of water flowing through a pore 

 of diameter 1 n (i. e., 1/25000 inch) would be about 15 x KM> CC. per year. . . . 

 Now, if we make the very generous estimate that 10 per rent of the volume occupied by 

 the rock consists of pore spaces . . . the quantity of water Bowing would be only 

 15 cc. per sq. cm. of surface per year. . . . Tf the diameter of the pores is 0.01 n 

 the amount of water flowing would he O.ooi.l cc. per sq. cm. of surface per year. . . . 

 Tn other words, a period of i.ooo years would be required for a quantity o\' water equiva- 

 lent to 1.5 cms. (about one-half inch) of rain to How past a given horizontal plane. 



". . . It appears, therefore, as if the probabilities were all against the notion that 

 appreciable amounts of meteoric water can ever penetrate into deep-seated and highly 

 heated rock-masses." (John Johnston and L. II. Adams: "Ohsrrva t ions on the I>aubr«V 



experiment and capillarity in relation to certain geologic speculationi," Journal of 



Geology, vol. 22, in press. 1013.) 



XLII — Bull. Gicol. Soc. Am., Vol. 24, 1912 



