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large volume of water, upwards of 
SURE See 
: 
Thermal Conductivities of Marble and Slate. 439 
From this preliminary investigation we drew the conclusion 
that the conductivity of our specimen of marble was practi- 
cally constant between 0° and 100°. On plotting the curve it 
appears that the apparently greater conductivity at higher tem- 
perature is due to a real difference of conductivity at all tem- 
peratures between the four hotter and three colder slabs, 
though all were cut from a single block of white Carrara 
marble. 
Readings were occasionally taken of thermopiles in the 
different interspaces placed within 2™ or 3™ of the edges of the 
slabs. The agreement was so close with those taken at the 
middle of the slab that it was evident that the law of temper- 
ature distribution on the edges exposed to the air was such 
that a much smaller slab might have been used. 
In order to extend the limit of our investigation to higher 
temperatures we were obliged to make some changes in the 
details of our apparatus. The use _ 
of a slab 30° square made it 
possible to construct a much more 
convenient apparatus, which is 
shown in fig. 2. As it was not * 
intended to observe the absolute 
conductivity, the troublesome ice 
box was replaced by a closed iron 
drum, D, containing a rotary stirrer 
and scraper turned bya motor. A 
20 kilograms per minute, flowed 
through the drum, D. Special 
arrangements for obtaining a large 
supply of water at a constant tem- 
perature were at our service in the 
laboratory, but a simple connec- 
tion with the city supply gave us 
a very uniform temperature of 
about 20°. 
The hot chamber was the iron box, B, planed on its upper 
surface and communicating at the bottom with a retort cham- 
ber, C, in which about 20 kilograms of mereury were kept boil- 
ing. The outlet at f allowed the vapor to escape to the tube 
g connecting with a large wrought iron chamber, where it con- 
densed and flowed back into the retort through the trap A. 
It was thus found possible to maintain a temperature of 
about 355° C. for many hours at a time. A very elaborate 
system of inch-thick asbestos jackets was found necessary 
on the hot box and all parts of the distilling apparatus. This 
is not shown in the figure. The arrangement of the thermo- 
