1886.] 



On the Specific Heats of Minerals. 



251 



process is involved with no more liability to error than the process 

 of weighing a body in air and in water. If, however, accuracy 

 — greater than 1 per cent. — be desired, the operation takes con- 

 siderably more time, as it is necessary, in securing t x accurately, 

 to leave thermometer and specimen a sufficient time together in 

 the calorimeter. The simplicity of the method is perhaps best in- 

 ferred from the fact that of over 130 experiments on minerals there 

 were but three spoiled — due to mishaps ; and it will be seen that the 

 repetition experiments reveal in no case appreciable discrepancy. 



That this specific heat constant is very sensitive to the presence of 

 impurities or variations in the chemical nature of the substance can- 

 not be considered a disadvantage. It is supposable that this might 

 lead occasionally to useful enquiry. This sensitiveness is shown in 

 the case of taurmaline. Of three specimens the specific heats 

 were — 



Hemihedral, black crystal = 0*2000 



Striated, black crystal — 0-2008 



Hemihedral, brown crystal = 0*2111 



The same, a second experiment .... = 0*2112 



The variation from the black to the brown is over 5 per cent. Now 

 tourmaline experiences considerable variations in the two con- 

 stituents iron and magnesium. Approximately in percentage com- 

 position according to Dana's table of analyses — 



FeO. Fe 2 3 . MgO. 

 Black tourmaline contains .... 6 8 1 



Brown tourmaline „ .... 1 11 



which in view of the high molecular heat of magnessia and the low 

 molecular heats of the oxides of iron would account for the differences 

 in the experiments. It will be seen later in the particulars of these 

 experiments that the densities of these crystals also, in a less degree, 

 reveal the difference in composition. 



Again attention is suggestively drawn by the thermal constant to 

 the chemical compositions of the first two of these three aerolites 

 from the Museum of Trinity College. 



(1.) Fell in Co. Limerick, September 10th, 1813 0'1787 



(2.) Fell in Maryland, U.S.A., February 10th, 1825. . . . 0*1785 

 (3.) Fell in Spain, July 8th, 1811 0*1856 



The specific gravities, too, of the first couple, are found to be 

 identical, thus: (1) =3*604; (2) =3*601; (3) =3*435. The experi- 

 ments, in fact, evidently afford strong reasons for believing that the 

 first two aerolites constitute a case of the strange similarity alluded 

 to by Daubree : — " II y a des meteorites eloigners au double point de 



