294 University of California Publications in Geology [Vol. 13 



Hoping to throw some experimental light upon the problem, I 

 sought the help of the laboratory with the following results : 



A hole one inch in diameter and three inches deep was bored in 

 a block of coarsely crystalline marble eight inches long and about 

 three inches in average cross-section. The block was then suspended 

 in a steam chest and for two weeks subjected to a steam pressure 

 of 60 lbs. for about nine hours per day, the steam being shut off at 

 night. At the end of that time it was assumed that the alternations 

 of pressure had induced the saturation of the rock with water. The 

 hole was then about half filled with commercial sodium sulphide satu- 

 rated and covered with water; a cork was inserted; and the cork 

 and rock surface for an inch or two about the hole were covered over 

 with several successive layers of a hot cement consisting of resin and 

 beeswax. The rock was then placed, cork up, in a battery jar on a 

 layer of pure beach sand about an inch and one-half thick. A strong 

 solution of lead acetate in tap water was poured into the jar about 

 the rock until it reached nearly to the cement on the top of the block. 

 In order to exclude the air and other impurities from the jar, a layer 

 of paraffin nearly one-quarter of an inch thick was poured over the 

 surface of the acetate solution so that it made a firm union with the 

 jar on the one hand and the rock on the other. This accomplished, 

 the cemented top of the marble block projected above the paraffin seal, 

 and was exposed to the air in such a manner that any capillary leakage 

 of the sodium solution under the cement would be evaporated before 

 it could reach the lead acetate solution beneath the paraffin seal. 



When the lead acetate solution was made up with tap water a 

 white precipitate at once formed, due perhaps to the presence of car- 

 bonic acid or chlorine in the water; but this soon settled making a 

 white layer over the sand and leaving a clear solution of lead acetate 

 above. Three weeks elapsed without any change being noted within 

 the jar, but in the middle of the fourth week it was noted that the 

 sand was becoming dark colored. Not believing it possible that the 

 sodium sulphide in the cell could diffuse out in such a short time, even 

 though the cell wall where thinnest was an inch thick, I did not visit 

 the experiment for several days thereafter. When next I observed 

 the jar I found the sand quite dark gray, and even black in places, 

 and a pronounced black precipitate upon its surface, the white layer, 

 which was originally there, being apparently much reduced. Fearing 

 a leak had developed somewhere, I broke the paraffin seal and with- 

 drew the marble block. A careful inspection showed that no leak 



