350 STUDIES FOR STUDENTS 
After removing the samples from the basin, the water adhering 
to the surface should be deftly removed by the use of bibulous 
paper, the samples transferred to the scale pan, and quickly 
weighed.. Through the transference of the samples from the 
basin to the scale pan there are two sources of error, one is 
through the use of bibulous paper, and the other through 
evaporation. No plan has yet been devised to avoid these 
SOunees of efron, wheretore theyslall and, Vudementyormrnc 
operator must be depended upon. 
After these weights are recorded the samples should be 
suspended by a silk thread in distilled water and again weighed. 
After this weight is recorded the samples should be transferred 
to a hot air bath and dried at a temperature of 110° C. until the 
interstitial water has been entirely expelled. The samples are 
again weighed and the results recorded. From the weights 
thus obtained the specific gravity is determined by dividing the 
average of the two dry weights by the difference between the 
average dry weight and the weight of the cube suspended in water. 
The apparent specific gravity can be readily obtained by 
subtracting the weight of the sample suspended in water from 
the weight of the sample saturated with water and dividing the 
average dry weight by this difference. 
Porosity and ratio of absorption.—These terms have been used 
interchangeably as applying to the percentage of the weight of 
the absorbed water to the average weight of the dry sample. 
This ratio, however, is not the percentage of actual pore space, 
but simply the relation between the weight of the rock and the 
weight of the water absorbed. The term porosity should only 
be applied to the percentage of actual pore space in the rock 
while the ratio of absorption should be restricted to the percent- 
age of the weight of the absorbed water to the average weight 
of the dry sample. The former gives the volume relation and 
the latter the weight relation. To my knowledge no American 
writer has computed the actual pore space or porosity of 
building stones. However, I believe that this determination is 
more important than the ratio of absorption. 
