348 SOMES VO RS SAUD ENTS: 
example one author gives the following as the results of his 
experiments on three different stones." 
“| ait Weight in lbs. Per cent. of 
umber SPEC Cer awaty per cubic foot water absorbed 
COOMA earrenatraratoneteceveletel see orornae 2.6236 163.50 18.07 
CPOE GBM Aebateere ats rric ps ote nero nae 2.6166 163.07 32.62 
CRAB Ola oes aicree Bee eethe eyes 2.5380 158.17 8.71 
It will be observed as a result of these experiments that the 
stone which absorbed 18.07 per cent. of water weighed more than 
the one that absorbed only 3.62 per cent., although the differ- 
ence in specific gravity is only .007. 
Another author says: ‘If we find that a stone has a specific 
gravity of 2.65 .... we get its weight by simply multiplying 
255. Dy 2:05) which eaves USP 05.02...) 4) sinetiMssstavemlenme 
reference is made to the “specific gravity proper’’ and not the 
‘apparent specific gravity.”’ Results obtained in this way would 
obviously be incorrect. Similar inaccuracies in the determina- 
tion of the specific gravity and weight per cubic foot, occur in 
other published reports, but those above quoted suffice as illus- 
trations. 
I believe that the specific gravity should be determined on 
the principle laid down by Professor J. C. Smock3 and that the 
“apparent” specific gravity should only be used in computing 
the weight of ithe stone per cubic foot, ) Phere is mo; incon 
sistency in this, in so much as the commercial weight considers 
only the external volume and does not consider the stone as a 
geometric solid. At least there should be a recognized uniform 
method of computing the specific gravity of stone. 
The specific gravity proper of a rock can only be obtained 
by weighing the samples in air, at a definite temperature, after 
all interstitial water has been expelled; then weighing them, 
t Bulletin of New York State Museum, Vol. II, No. 10, Table, p. 358, by FRANCIS 
A. WILBER. 
2 The Building and Decorative Stones of Maryland. Maryland Geological Sur- 
vey, Vol. II, p. 119, GEo. P. MERRILL. 
3 Joi. 
