The Fusion Constants of Igneous Rock, 173 



As this expression is independent of c and a the function / 

 does not contain the quantity K, and it only involves L and 

 Gr in the form 2mJj — GP. We can best express this by 

 writing the function with variable 2mL — G 2 , instead of 

 L, G, when it becomes B •— f(2mh — G 2 ,H). If we introduce 

 again into this expression the general values given in equations 

 11 to 14, we see that the two variables in the function are 

 quite independent of each other if e, a, 13 are to have all 

 possible values. And since B is constant for all values of c, a, 

 and /3, it is so for all values of 2mL — G 2 and H, and is 

 therefore absolutely constant. The distribution of vis viva is 

 therefore obtained. 



XXII. The Fusion Constants of Igneous Rock. — Part II. The 

 Contraction of Molten Igneous Rock* on Passing from 

 Liquid to Solid. By Carl Barus f . 



[Plate V.] 

 Introductory. 



1. -\/fATERIAL and Method. — The following volume- 

 measurements were made for Mr. Clarence King, on 

 a typical sample of diabase which he furnished. 



The method of testing the volume-behaviour by allowing 

 the rock to expand in a vertical tube provided with an index 

 was suggested to Mr. King by Lord Kelvin. I therefore pre- 

 ferred it to a method of my own J, in which the behaviour in 

 question is to be determined by high-temperature air-volumetry, 

 with the rock enclosed in a glazed platinum bulb-and-stem 

 arrangement. In place of the index or float I employed an 

 electric micrometer, believing a probe of this kind to be more 

 trustworthy (§ 13) . I may state here, that the fact that the con- 

 traction of the magma in passing from liquid to solid can 

 actually be measured by the simple burette method was to me a 

 great surprise. After many trials I found, however, that by 

 allowing the furnace to cool so slowly that the platinum vessel 

 remained rigid relatively to the charge, the contraction of 

 the latter could be followed even into the solid state. As 

 a consequence of slow cooling, moreover, the magma was 

 probably undercooled, and I thus obtained the whole volume- 

 difference liquid-solid at a given temperature. The data are 



* Cf. note in American Journal, xlii. p. 498 (1891). 

 f Communicated by the Author. 



\ Cf. Phil. Mag. July 1892, where this method is tentatively employed 

 to measure the expansion of white-hot porcelain. 



