VOLCANIC TUFF. 399 



liquid. James Thomson "' calculated that the melting point of ice would be lowered 

 by n 0.0075° for an increase of n atmospheres. W. Thomson" confirmed this cal- 

 culation within a difference of 3 per cent by determining the melting point of ice at 

 8.1 and 16.8 atmospheres. . M. Mousson"- kept water liquid at — 5° by greatly 

 increasing the pressure and found that at a pressure of about 13,000 atmospheres, 

 ice melted at —18° to —20°. Calculated from the data of Thomson the value for 

 — 20° would be but 2,666 atmospheres, about one-fifth the value obtained by 

 Mousson. Assuming the smallest value, it is evident that there is no stone strong 

 enough to resist the strain produced by the freezing of any considerable quantity 

 of water within its pores. 



In the Philippines the abundance of rain and the high humidity of 

 the air keeps the stone moist dui'ing tlie greater part of the time. The 

 action of the water is markedly twofold, as a solvent for mineral matter 

 and as a solvent or carrier for the gases of the atmosphere. This tuff 

 hardens rapidly after being e.xposed to the air and this change is undoub- 

 tedly hastened by the presence of moisture. Table III shows an increase 

 of nearly 50 j)er cent in the tensile strength of Guadalupe stone which had 

 been exposed for some time. Majayjay stone which had been exposed 

 so long that it was considerably decayed, still had a tensile strength about 

 equal to that of the newly quarried stone. 



Cubic iveight. — The cubic weight of this stone as it is taken from the 

 quarry depends upon its specific gravity, porosity, and the water content. 

 With unifoi'm stone the only fluctuating quantity is the water content. 

 Owing to the very large poi'e space and the heavy rains in the Philippine 

 Islands we may expect this stone to absorb and give up water readily 

 and its cubic weight to vary between the limits for the thoroughly 

 air-dried sample and the satitrated one, namely, 1,375 to 1,655 kilos 

 per cubic meter (35.3 cubit feet). 



The rate at which this stone gives up its water in dry storage is also 

 an important factor in its transportation. 



Cubes of different sizes were carefully saturated with water and 

 suspended in the laboratory on a 1-centimeters-niesh wire net so that 

 evaporation could take place equally from all surfaces. The tests were 

 begun on March 23, 1908. The data and the results are as follows : 



^'' Trans. Roy. Soc. Edinburg (1849), 16, 575; Camb. and Duhl. Math. -J. (18.50) 

 5, 248; Ann. d. Chim. (1852), 35, 376. 

 "Phil. Mag. (3), (1850), 37, 126. 

 "Pogg. Ann. (1858), 105, 172; Ann. Chim. et Phys. (3), (1859), 56, 252. 



