1886.] 



On the Specific Heats of Minerals. 



259 



me approximate to 4*4. It is certain that the small quantities of 

 impurities present, acting merely by their atomic heats, would not 

 suffice appreciably to alter the sp. h., and would rather tend to 

 elevate it. 



To these cases may, perhaps, be added those of apatite and 

 oligoclase. I examined but two specimens of each. 



Apatite. 



Sp. h. Sp. gr. 



Translucent hexagonal prism, high lustre, brittle 0*1826 3*166 



Opaque, dull compact crystal ( 0*1920 3*089 



Oligoclase. 



Sp. h. Sp. gr. 



Sub-translucent, milk-white (Ttterby) 0*1997 2*621 



Transparent crystal O2059 2*605 



It remains to notice the cases of three chemically and crystallo- 

 graphically related minerals where the variations obtaining in each 

 case would appear to stand in a numerical relation from one sub- 

 stance to another. The minerals are iron pyrites (isometric di- 

 sulphide of iron) ; galenite (isometric sulphide of lead) ; sphalerite 

 (isometric sulphide of zinc). The orthorhombic disulphide of iron, 

 marcasite, seems also to fall into the relationship. 



The specific heat of pyrites is, according to Regnault, 0*13009. 

 Operating on a large bright cube, I obtained the same number exactly, 

 0*13009. Neumann's result is 0*127, Kopp's 0*126. The specific 

 heat of galena is given differently by Regnault, Kopp, and Neumann. 

 The value given by Kopp, 0*0490, closely agrees with an observation 

 of my own, 0*0492. I also obtained 0*0504 and 0*0522 on well 

 crystallised specimens. The last number is probably a little 

 excessive, as there was just a trace of a white substance — the 

 carbonate — present. There are found finally for pyrites and galena 

 the numbers — 



Pyrites. 



W 0*127 R 0*130 



K 0*126 J 0*130 



Galena. 



K 0*0490 R. . . . 0*0508 J 0*0522 N 0*053 



J.... 0*0492 J 0*0504 



Taking the means of the first two vertical colums in each case, the 

 proportion holds very closely 



Pyrites. Gralena. 

 126*5 : 130 :: 491 : 506. 



