TESTS OF GRANITE. (53 
PART II.— ECONOMIC FEATURES. 
The practical side of the granite industry will now be considered. 
The sections on the tests of granite and granite quarrying are of 
general application, but the rest of the matter has reference only to 
Maine granites and quarries. A list of the more important works on 
granite quarries and quarrying and other matters of economic char- 
acter will be found at the end, together with a glossary of both scien- 
tific and quarry terms. 
TESTS OF GRANITE. 
The testing of granite is a subject of considerable importance, as 
may be seen by its literature. As pointed out by Merrill, there is 
danger of attaching undue importance to tests of compressive strength 
alone, the results of which in nearly all cases far exceed the generous 
margin allowed by architects beyond that required by the weightiest 
structures. On the other hand, there is danger of losing sight of sev- 
eral other important qualities which ought to be carefully tested and 
upon which the economic value of granite in part depends. The fol- 
lowing tests include all the kinds made at European testing institu- 
tions or recommended by American authorities, as well as some sug- 
gested bv the investigation of Maine granites. 
Chemical analysis. — Chemical analysis is made in order to deter- 
mine the amount of iron and lime, or to detect anything abnormal in 
the composition. 
Determination of CaCO s . — Tests are made to determine the pres- 
ence of lime not combined with silicates in order to ascertain the 
percentage of CaCO.. (lime carbonate) present. This is done by 
powdering and treatment with warm dilute acetic acid. (See p. 94.) 
Test for discoloration. — The method applied by Daly (Bull. U. S. 
Geol. Survey No. 209, p. 52) seems to be well adapted for this purpose. 
A piece of fresh rock is immersed in a stream of carbon-dioxide 
gas for 20 minutes and then kept in an atmosphere of that gas for 
24 hours. Another piece of fresh rock is placed in an atmosphere 
of purified oxygen over night and then exposed for 30 minutes to 
a temperature of 150° C. (302° F.). Any discoloration due to the 
carbonization or oxidation of the minutest particles of any mineral 
would be sure to show itself under these tests. 
Mineral composition. — This is determined by the microscopic exam- 
ination of a considerable number of typical thin sections. All the 
mineral constituents are noted, and the average size of the mineral 
a See Bibliography, p. 184. 
