I 7 o RELATIONS OF SOIL TO HEAT 



Quartz Sand, Fine ... 100.0 

 Medium ... 103-6 

 Coarse ... 105-3 



Dry Quartz Powder = 100. Dry Clay = 100. 



Clay Powder 94-1 100-0 



with Limestone Stones ... 112-1 118-8 



Quartz Stones ... 115-6 ... 122-5 



2- In wet condition, not compressed 



Dry Quarts Powder = 100. Wet Quarts Poicder - 100. 



Quartz Powder 201-7 100-0 



Kaolin 155-6 77-1 



Chalk 153-2 75-9 



Peat 94-3 ... 46-8 



Quartz Sand, Dry ... 100 



Moist ... 174 



Wet ... 189 



Of all the soil constituents experimented with, quartz 

 showed, under every circumstance, the highest power of con- 

 ducting heat ; in this respect indeed it exceeds at least one 

 of the metals, namely bismuth. The conductivity of every 

 substance is greatly lessened when it is in the form of powder ; 

 the finer are the particles of the powder the less is the power 

 of conducting heat. The comparative conductivity of different 

 substances cannot therefore be ascertained from experiments 

 on their powders, unless the powders are in every case com- 

 posed of particles of the same size ; the results obtained by 

 Pott are thus only strictly true of the particular powders 

 which he examined. The diminution of conductivity observed 

 in a powder is due to the small extent of contact among 

 the particles ; in the case of a dry powder each particle is 

 surrounded by air, in a wet powder each particle is enclosed 

 by water. The far greater conductivity of a solid rock than 



