290 Dr. H. F. Weber on the Specific Heat of 



C 18 o_ 98 .= 0*2415 for wood carbon, 

 C 19 o_ 90 c =0*2608 for animal carbon, 



are only to be accounted for (as Regnault himself suggests) by 

 the supposition that heat is evolved when the porous carbon 

 comes into contact with the water of the caloriuieter. That a con- 

 siderable amount of heat is thus really evolved (an amount suffi- 

 cient, if taken into account, to reduce Regnault' s number to the 

 real number, viz. 0*1935 for porous carbon, C^go) appears from 

 the following experiment. 



The glass tube containing the porous carbon used in the fore- 

 mentioned experiments was drawn out at one end and then 

 broken so as to have an orifice about 1 millim. wide. The tube 

 was heated to 99°*1 for forty-five minutes, and then quickly 

 plunged into the ice-calorimeter; the water in the calorimeter 

 rose in the tube so as to wet the carbon. The circumstance that 

 in this experiment the mercury thread did not come to rest for 

 thirty-two minutes, while at other times after twelve to fifteen 

 minutes no further movement was observable, showed that an 

 evolution of heat followed upon the wetting of the porous carbon 

 by the water. This becomes more evident from the following 

 data :-— 



1*410 grm. carbon ) cooled from 99°'l to 0°, j gaveup57'06heat- 

 1*104 grm. glass > during which time the car- > units in the calori- 



0*655 grm. platinum ) bon was wetted with water, ) meter. 



Erom these numbers, and from the known mean specific heats 

 of the glass and platinum employed (C - 99 .i = 0*201 7 and 0*02323 

 respectively), the number C _ 99 .i =0*2355 is deduced as the mean 

 specific heat of the porous carbon wetted in the calorimeter, a 

 number which agrees very well with Regnault's C 18 _9 8 =0*2415. 

 The above experiment gives for porous unwetted carbon the 

 number C _g 9 .2 =0*1935. A unit weight of porous carbon, as far 

 as possible free from water, evolves 4*16 heat-units when wetted 

 with water. 



III. The Specific Heat of Crystallized Boron. 



Two hundred small octahedral crystals of boron, kindly given 

 by Professor Rammelsberg, were used. These crystals, having 

 been prepared by heating boric acid with aluminium, could not 

 be considered perfectly pure. The total weight of boron was 

 671 milligrms. The substance was placed on a small vessel of 

 tinfoil weighing not more than 0*1 grm. On account of the 

 small weight of this tinfoil and its relatively low specific heat, it 

 was possible to determine the specific heat of the boron with 



