QUARRY MATERIALS OF NEW YORK 39 



dioxide afford a measure of the freshness of the rock, but should 

 be supplemented by microscopic study. The sulphur establishes 

 the relative proportions of the sulphides — pyrite, marcasite or 

 chalcopyrite. 



The presence of carbonates in igneous rocks can be quickly 

 determined by powdering a little of the sample and treating with 

 very dilute hydrochloric acid or equal amounts of acetic acid and 

 water. If carbonates are present, bubbles will form around the 

 powder and gradually rise- to the surface. 



PHYSICAL TESTS 



The laboratory testing of stone is an attempt to ascertain the 

 resistance which the material will offer to the various stresses that 

 arise in engineering and architectural structures. The practice 

 has but recently come into favor in this country, but it has been 

 followed abroad for a longer time. The general interest now taken 

 in the subject may be ascribed largely to the initiative of the 

 engineering staffs connected with highway and other public 

 improvements. 



One of the first reports on quarry materials to give attention to 

 their physical testing and to embody a fairly comprehensive series of 

 results is Smock's " Building Stone in New York." 1 The data of 

 the tests relate to specific gravity, absorption, the action of acids, 

 change of temperature and the influence of heat. 



It is well to note that the capacity of a rock to resist the many 

 variations of strain can not be estimated by any single physical 

 test. Crushing strength alone means little as to the quality of stone 

 for use in street work or its probable behavior when placed in an 

 arch. Moreover, physical tests of any kind do not fill the place 

 of microscopic investigation of the mineral association and textures 

 of rocks and their full value is attained only when they are com- 

 bined with the results of study into all the general properties of the 

 materials. 



The most comprehensive work on the subject of testing of stone 

 undoubtedly is Hirschwald's " Handbuch der Bautechnischen 

 Gesteinspriifung," which has already been referred to. The work 

 is a scientific exposition of the subject based on actual results ob- 

 tained by the use of various physical, chemical and microscopic 

 methods of investigation. The volume was issued in 1912 so that 



1 N. Y. State Museum Bui. 10. 1890. 



