PAE PROPE RIMES ORB ULE DING SRONES, LTC: 341 
effects of carbonated or acidulated waters, can be determined by 
the microscopic examination of thin sections. 
It is thought that the use of the microscope, with an intel- 
ligent interpretation of the facts revealed thereby, might eventu- 
ally render unnecessary the performance of the physical tests 
and the determination of the chemical composition. However, 
at the present time, this method is only available to the scientist 
who can interpret the facts thus observed. The accuracy of 
his conclusions will depend upon his judgment and experience 
as a petrographer. With the public it may never supplant the 
physical tests, because it lacks the quantitative element. 
PHYSICAL TESTS 
The purpose of the physical tests is to determine by artificial 
methods the strength of a stone and its capacity to resist the 
destructive agents encountered in actual use. As stated on a 
previous page, the signs of decay in buildings, on account of the 
improper methods of quarrying, handling, dressing, and laying 
are not always evidence of inherent weakness in the stone. For 
this reason the physical tests, performed in the laboratory, often 
provide a more reliable basis on which to estimate strength and 
durability. 
It is a comparatively simple matter to determine the strength 
and elasticity of a stone, both of which can be measured directly 
by machinery. It is a more difficult problem, however, to 
express quantitatively the durability, on account of the impos- 
sibility of measuring in a few weeks or months in the laboratory 
any deterioration that might take place under ordinary climatic 
conditions. Further than this the conditions in nature change 
from day to day, both in intensity and kind, and as a rule, there 
are several instead of one agent of destruction operating at the 
same time. In order to measure the effect of these agents in 
the laboratory it is necessary to consider them separately, and 
on such a grossly exaggerated scale that there will be accom- 
plished in a brief period, what in nature would require many 
years. 
