4 Day, etc. — Determination of Mineral 



Direct Measurements. — In addition to the estimates obtained 

 by these indirect methods, direct measurements of the volume 

 change accompanying the liquefaction of rocks and minerals 

 have been attempted. The most of these have depended: 

 (1) upon the floating or sinking of a solid body in the molten 

 rock ; ^2) upon direct measurement of the volume changes in 

 a given mass of molten material. 



Observations are on record of the floating or sinking of lava 

 crusts in liquid lava and of the floating of solid bodies thrown 

 into lava lakes.* The data are contradictory and unsatisfac- 

 tory. The floating of lava crusts is usually due to their spongy, 

 porous structure ; in the lava lake of Kilauea, for instance, 

 these crusts sink rapidly when freed from their entrapped or 

 supporting gases. 



Flotation experiments on a small scale, with molten rocks, 

 artificial silicates, or metallurgical slags, have also yielded contra- 

 dictory results. Whitley,t in 1878, concluded from such exper- 

 iments that there is contraction in the liquefying of basalt and 

 of iron-furnace slags. Doelter,;}; in 1901, from the sinking or 

 floating of solid bodies of various densities, concluded that there 

 is a net expansion in the liquefying of melanite, augite, and 

 several rocks, and estimated its amount. As no account seems 

 to have been taken of the expansion of the test substances, the 

 results have little quantitative value. Doelter later improved 

 the method by using a platinum sphere ; § he estimates from 

 measurements made with the new apparatus that the density of 

 liquid diopside near its melting point is 2'8. Fleischer || takes 

 the opposite view, that lavas expand in solidifying ; his argu- 

 ments, drawn from a variety of laboratory data of a rather 

 indirect kind, are unconvincing. 



Nies and Winkelmann^f obtained no satisfactory results by 

 the flotation method. The earlier literature is well summarized 

 in their articles, which, however, are concerned chiefly with 

 metals. 



Measurements of the actual expansion or contraction of mol- 

 ten slags and lavas began with Bischof** about 1838. He esti- 

 mated a total contraction of from 10 to 25 per cent in passing 

 from the molten to the cold crystalline condition, in basalt, 

 trachyte, and granite. Similar measurements were made by 



*See F. Zirkel, Lehrb. d. Petrogr., i, 684, 1893. 



f Nature, xviii, 397. 1878. 



X Neues Jahrb. Min.. 1901, II, 141-157. 



§ Doelter and Sirk, Sitzb. Wien. Akad., cxx, i, 659-670, 1911. 



I A. Fleischer, Zeitschr. Deut Geol. Ges., lv, 56-68, 1903; Ivii, 201-214, 1905; 

 lxix, 122-131, 317-321. 1907; lx, 254-258, 1908. 



..IFF. Nies and A. Winkelmann, Ann. Phys. (2), xiii, 43-83, 1881. F. Nies, 

 Tiber d. Verhalten d. Silicate beim tJbergang aus dem gluthfliissigen in den 

 festen Aggregatzustand, Stuttgart, 1889. 



** Neues Jahrb. Min., 565, 1841 ; 1-54, 1843. 



