. A treatise on rocks, rock-weathering and soils;. Petrology; Soils. 40 PHYSICAL AND CHEMICAL PROPERTIES OP ROCKS 2S663 Bridaeparf) Calv dental air bubbles—and finally pressed flat down against the stone film. The film itself, if sufiiciently warmed, no longer ad- heres to the thick glass, and may be removed to the clean slip for its final mounting. This is best accomplished by taking up the thick glass by means of a pair of forceps and push- ing eover-giass and film together, with a needle point set in a handle, off into the balsam on a new slide. The cover-glass here serves merely as a suppo
. A treatise on rocks, rock-weathering and soils;. Petrology; Soils. 40 PHYSICAL AND CHEMICAL PROPERTIES OP ROCKS 2S663 Bridaeparf) Calv dental air bubbles—and finally pressed flat down against the stone film. The film itself, if sufiiciently warmed, no longer ad- heres to the thick glass, and may be removed to the clean slip for its final mounting. This is best accomplished by taking up the thick glass by means of a pair of forceps and push- ing eover-giass and film together, with a needle point set in a handle, off into the balsam on a new slide. The cover-glass here serves merely as a support for the thin film during the process of transferring. "Without it there is danger of breakage. When fairly transferred, the new slide is removed from the hot plate, the cover pressed close down against the film, adjusted in proper position and allowed to cool. The superfluous balsam may be then removed with a hot knife and the section finally washed in alcohol. Thus completed, it forms the ''thin section" of the petrologist. Plagmdase. feldspars Fig. thin section of roek. 2. THE SPECIFIC GRAVITY OP BOCKS The term specific gravity is used to designate the weight of any substance when compared with an equal volume of distilled water at a temperature of 4° C. This property is therefore dependent upon the specific gravity of its various constituents and their relative proportions. The exact or true specific gravity of a rock may be obscured by its structure. Thus an obsidian pumice will float upon water, buoyed up by the air contained in its innumerable vesicles, while a compact obsidian of precisely the same chemical composition will sink almost instantly. This property of any subject is spoken of as the apparent specific gravity in distinction from the actual com- parative weight, bulk for bulk, of its constituent parts, which could in the case of a pumice be obtained only by finely pul- verizing so as to admit the water into all its pores. Inasmuch a
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectpetrolo, bookyear1913
