174 Mr. Carl Barus on the Fusion 



sufficient to compute the corresponding contraction at other 

 temperatures. 



2. Literature. — The question has elicited voluminous dis- 

 cussion ; but literary comments are superfluous here, since 

 Prof. F. Niess* , of Hohenheim, not long ago made a careful 

 survey of all that has been done on the subject. The reader 

 desiring specific information is referred to this interesting 

 pamphlet. " Es ist ein durch Contraste buntes Bild," says 

 Prof. Niess (loc. cit. p. 36), "welches in der vorstehenden 

 Citatenlese dem Leser zu entrollen war, und aus dem 

 Wirrwarr entgegengesetzter Ansichten heben sich nur zwei 

 Korper : Wismuth und Eisen, heraus, iiber welche man wohl 

 mit absoluter Sicherheit die Acten als geschlossen bezeichnen 

 kann, und zwar in dem Sinne, dass fur sie die Ausdehnung 

 im Momente der Yerfestigung als zweifellos bewiesen gelten 

 kann. Die iibrigen Metalle stehen noch im Streit, und fur sie 

 gilt dasselbe was wir fur die kunstlichen Siiicate zu fordern 



hatten " Now iron, in virtue of the occurrence of 



recalescence (Gore, Barrett), is scarcely a fair substance to 

 operate upon; and it heightens the confusion to find that 

 Prof. Mess, after weighing all the evidence in hand, is 

 obliged to conclude that rocks expand on solidifying. 



The present experiments show beyond question, I think, 

 that at least for diabase this is not true. I find that this 

 rock not only contracts between 3*5 and 4 per cent, on solidi- 

 fying, but that such solidification is sharply broken and only 

 apparently continuous with temperature, and that the fusion- 

 behaviour throughout is quite normal in character. Hence, 

 with certain precautions which I shall adduce in the course 

 of this paper (§ 21), the volume thermodynamic relations 

 which I derived by acting on organic bodies may be applied 

 to rock magmas. 



3. Effect of Fusion. Density. — The rock after fusion is 

 changed to a compact black obsidian, and quite loses its 

 characteristic structure. It was therefore important to examine 

 the volume-relations of this change, preliminarily. This is 

 done in Table L, where the densities obtained with lumps of 

 the rock (mass M) at the temperature t are given, A being 

 the density before, A' after fusion. 



* " Ueber das Verhalten der Silicate etc.," Trogramm zur 70. Jahresfeier 

 d. k. Wiirtemb. landw. Academie, Stuttgart, E. Koch. 1889. Cf. Niess u. 

 Winkelmann, Wied. Ann. xiii. p. 43 (1881) ; xviii. p. 364 (1883). 



