394 



cox. 



wall. It is difficult to say what is the effect of long continued pressure 

 upon a stone under this condition, but the majority of architects estimate 

 that ten or twenty times the strength to which it is actually subjected is 

 required. The data are as follows: 



Table I. — Crushing strength of andesitic tuff from near Manila. 



Source. 



Number 

 o£ deter- 

 mina- 

 tions 

 made. 



Average 

 area of 

 bearing 

 surface. 



Ultimate strength per 

 square centimeter. 



Maxi- 

 mum. 



Mini- 

 mum. 



Aver- 

 age. 



Manila, quarry unknown. 



Guadalupe quarry 



Baliuag 



Majayjay, Laguna quarry 

 Do.« 



Sq. cm. 

 73.3 

 93.5 

 54. 



Kilos. 

 101 

 42 

 205 

 194 

 157 



Kilos. 

 85 

 30 

 110 

 166 

 141 



Kilos. 



151 

 181 

 149 



• An old stone which had been used many years in a building, 

 of decay. 



It showed marked sign 



Using the average value given for the Majayjay quarry stone and the 

 weight for the wet stone as 1,655 kilograms per square meter (given on 

 p. 399) it can be computed that a wall 110 meters high would be 

 required to equal the compression strength of the stone. Using tlie 

 safety factor 10, this would be suitable for the erection of structures 

 eleven meters high. 



Much of the stone from the Meycauayan quarries. Province of Bulacan, 

 which supply stone to Manila is of this class and is fairly durable. Tlie 

 stone formerly quarried in Guadalupe seems to be better than that which 

 is now being taken out. Probably many of the best quarries there and 

 possibly elsewhere have been lost sight of, for recently quantity rather 

 than quality has been sought, i. e., no attention has been paid to sys- 

 tematic testing and that stone which was most accessible has been 

 worked regardless of its grade. 



Eondelet's rule that the resistance of a stone to crushing is only three 

 times that offered to traction does not hold for volcanic tuff. 



The tensile stre7igth of a stone is its ability to withstand a pulling 

 stress. This has been determined for several samples. These determina- 

 tions were made by cutting blocks of the stone of the ordinary size and 

 shape of a cement briquette and breaking them in a standard machine. 

 The rate of the shot in all of these tests was 183 kilos per minute, that 

 adopted by the United States Army in their specifications for cement. 



Three samples of stone which to my knowledge have been quarried at 

 least two years, taken from various sources in Manila, showed the fol- 

 lowing tensile or breaking strength. 



