62 



REPORT 1879. 



corrected data of thermal properties of certain vert porous 



Rocks, 1879. 



Rock-specimen ; or sub- 

 stance tested 



!{ 



Sandstone (Godstone ; f 

 greensand) . . . \ 



Firestone (Godstone 

 greensand) . . 



Building Limestone f 

 (Caen, Normandy) . \ 



Building Limestone f 

 (Gt. Pyr., Casing- < 

 stone) L 



Magnesite,' white [" 

 amorphous (Pi 

 nerol, Genoa) 



Magnesian Limestone 

 (porous ; much mag- 

 nesia ; Castle Eden, 

 Durham) .... 



Chalk (Godstone, Sur- 

 rey) 



Pumice stone. . . . < 



Fine Plaster-of- Paris / 

 (a light plate) . . \_ 





{ 



Specific heat. 

 Dry (wet) 



By 

 weight 



C 

 (1879) 



By 

 volume 



c 

 (1879) 



0-22 

 (0-36) 



0-22 

 (0-36) 



0-21 

 (0-30) 



0-20 

 (0-30) 



•24 

 (35) 



0-19 



(0-31) 



0-21 

 (0-35) 



0-24 

 (0-57) 



0-26 

 (0-51) 



033 \ 



(0-66)/ 



0-35 \ 



(0-66)/ 

 0-43 \ 



(0-66)/ 



0-43 1 

 (0-67) f 



0-36 

 (0-70). 



0-14 

 (0-61) 



0-27 

 (0-79) 



Values obtained by 



Earlier and erroneous 

 reduction-factor 

 (196), 1874-78 



Absolute dry 

 _ (wet) 



Conduc- 

 tivity 

 k 



•0021 

 •0043 



•0040 



•0053 



•0020 



•0005 

 (■0010) 



•0012 

 (•0016) 



Resis- 

 tance 



Ratio 



k 



c 



(1879) 



New and correct reduc- 

 tion-factor (220), 

 1879 



Absolute dry 

 (wet) 



Conduc- 

 tivity 



(2) 



474 

 231 



250 



188 



500 



1818 



(971) 



833 



(625) 



0*; 



•0059 

 •0102 



•0092 



•0155 



■0056 



•0038 

 (•0017) 



•0045 

 (-0020) 



(4) 



•0024 

 •0049 



•0045 

 •0044 



•0060 



•0022 



•0006 

 (•0012) 



•0013 

 (•0018) 



Resis- 

 tance 



v ; 



421 

 205 



222 



167 



445 



1616 



(863) 



740 



(555) 



Ratio 

 k 



(6) 



•0066 

 •0115 



•0104 

 •0098 



•0174 



•0063 



•0043 



•0019 



•0051 



(0023) 



1 New observations of the specific heats of Magnesite, and of Frost erley and Dent 

 marbles, have shown that the numbers found for them last year are fallacious. The 

 specific heats by weight and volume of the last two rocks are really ; Frosterley, -21, -57 ; 

 Dent, -22, -60, which agree very nearly with those which have been observed in the other 

 limestone and marble specimens of the list. When corrected for the known weight of 

 water which it absorbed in boiling, the specific heat by weight of Magnesite observed last 

 year becomes 0-175 ; lower than that of limestone, instead of higher as should be expected 

 from this rock's lighter molecular weight. The real value now found of its specific heat is the 

 exceptionally high one 0-245 ; a specimen of hard crystalline magnesite from Trieste also 

 giving 0-244. Compared with Regnault's specific heats of some earthy carbonates, and 

 with their molecular weights, this high specific heat of magnesite appears to be quite in 

 accordance with the low place which it occupies among those carbonates in its combining 

 weight, thus : — 



