214 



Profs. W. King and T. H. Rowney. 



[June 19 r 



It is evident from the above tables that acetylene is governed by 

 the same laws as other compressible liquids, that is to say. its com- 

 pressibility increases as the temperature rises, bnt diminishes as the 

 pressure increases. For instance, at a pressure of 95 atmospheres it is 

 three times as compressible at 35° C. as at 0' C. 



The volume being the same, the compressibility appears to be nearly 

 fche same at different temperatnres, which is really due to the curves at 

 high pressures running nearly parallel, thus introducing a correspond- 

 ing' difncultv in the estimation of small differences. 



On comparing the compressibility of liquid acetylene with the 

 results obtained by M. Amagat (" Annales de Chem.," 1877) in the 

 case of benzene, it appears to be about seven times as compressible as 

 the latter body, at a temperature of 16° C, and under a pressure of 

 40 atmospheres. The comparison could not be carried out at higher 

 temperatures, for whereas M. Amagat reaches a temperature of 100° C. 

 with the benzene, I was not able to go beyond 35° C. with the 

 acetylene. 



XIX. On the Origin of the Mineral. Structural, and Chemical 

 Characters of Ophites and related Rocks.' 5 By Professors 

 W. KING, Sc.D., and T. H. Rowney. Ph.D. Communicated 

 by the Treasurer. R.S. Received May 12, 1879. 



(Abstract.) 



The authors, beginning with (A) " The different kinds of rocks 

 treated of," in their memoir, divide them into two groups. The first, 

 " Silacid Ophites." is represented by serpentinite (common at the 

 Lizard) and other rocks, essentially composed of serpentinous minerals : 

 it includes a subsection, comprising peridolites and some others, all 

 slightly hydrated. The second, t; Silocarbacid Ophites," consists of 

 rocks, which, in addition to serpentinous minerals, contain a mineral 

 carbonate — for example, ophi-calcite : its subsection is represented by 

 hemithrenes. The relation of the first group, through its subsection, 

 to ordinary metamorphic rocks, also of the second group, through its 

 subsection, to carrarites and dolomites is pointed out. 



As regards (B) " Their mineral character," it is stated that ophites, 

 &c., embrace some fifty or more different minerals, all containing 

 more or less hydrous silicate of magnesia ; in addition to which, dry 

 silicates and carbonates are often present. The relation of these 

 minerals to others, essentially anhydrous, as hornblende, diallage, and 

 peridote, is noticed. 



Treating on ( C) The structural character of ophites. &c," the 

 protean nature of their essential mine al. serpentine, is shown by 



