VARIATIONS OF SPECIFIC GRAVITY." 



By (i. W. A. Kaiilijaum. 



In connection with researches on the distinction of metals, and 

 while seeking to fix the specific gravity ot" the pure metals employed, 

 I was led to make a tliorongh study of the subject of specific gravity 

 measurements.'' The grounds which led me to l)estow so much atten- 

 tion on this subject apparently so threadbare are these : First, the 

 exact measurement of specific gravity, particularly' for solid bodies, 

 is an extremely difficult piece of work, which can be successfully 

 accomplished only by attending to certain not unimportant pre- 

 cautionary measures; and, second, the specific gravity to be deter- 

 mined is to be regarded rather as the expression of particular prop- 

 erties of the individual specimen examined than as a general ])roperty 

 of all solids of the same kind. 



This latter statement may be illustrated by the following determi- 

 nations made on a small block of the purest Norwegian converter 

 copper refinings, for which chemical analysis yielded i)!).9'2 per cent 

 copjjer. 0.O2 per cent silver, 0.04 per cent nickel, and 0.0*2 per cent iron. 

 Three small bars, (> nun. in diameter and 45 mm. in length, were pre- 

 pared, containing about 1.'25 cm'' each, and their specific gravity was 

 determined within a mean error of 0.0010, as follows: I, 8.4412: II, 

 8.r)92() ; III, 8.121)7. 



Thus it appears that three cylinders, turned from a single small 

 block of copper, showed a variation of specific gravity through a 

 range of 0.2021), or over 8i per cent of the whole specific gra\'ity. 

 Inasmuch as this was cast copper it was easy to cxj^lain the cause of 

 the variation, for probably there were faults oi- blowholes in the 

 casting. But the interesting and natural (luestion arose. Where and 

 when do such faults cease entirely? 



With another cylinder of the same copper, weighing 70 grams, I 

 made careful measurements b}' the volumetric method, depending 



o Translated, by permission, from Annalan der Pliysilc. Leipzig, No. 8, 1904. 

 b(i. W. A. Kahlbaum, Zeitscli. f. anoi-j;. Chew. -J!*, pi.. l'.»7-213, 1902. 



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