Chemical Science, 473 



to be placed on a thick mass of the substance to be tried, and the 

 fall of temperature in a given time noted as before ; striking effects 

 were thus obtained. Being first applied to iron at the temperature 

 of 8° C, and then upon a mass of stone, the difference at the end 

 of the second minute was 5°. The differencesarje n?,ujch greater 

 when iron is compared with brick or wood. .iiHifl) yl) ^ »' 



Although the conducting powers thus obtained for different 

 substances are only approximations, yet there are many bodies, as 

 bricks, stones, wood, clothing,. &o*,i for. wlJWh..ith«eei)ar«)4iuite 



sufficient. fjt wh /f)i// ^.hnm ^'rriMndionyM ; 



Another still more delicate method of ascertaining tne con- 

 ducting power of bodies is then described, but it is also more 

 difficult. Two vessels are used ; the lower one is maintained at a 

 constant temperature, as 100° C. j upon that is placed the substance 

 to be tried, and upon tliat again the upper vessel. The lower 

 part of the upper vessel is inclosed, and constitutes the bulb of an 

 air thermometer j the upper part is retained at the temperature of 

 ice J the air therefore in the thermometer is cooled by the ice and 

 warmed by the lower heated vessel ; the latter producing an 

 effect greater or smaller according to the nature of the substance 

 between it and the air-vessel j the temperature of the air and the 

 indication upon the scale connected with it soon becomes perma- 

 nent, and as it is higher or lower, indicates the greater or less 

 conducting power of the interposed substance. When the experi- 

 ments are carefully made, they accord with those of the former 

 instrument, but are more delicate. 



By means of these instruments, M. Fourier was able to ascer- 

 tain that many substances when put together conducted heat dif- 

 ferently, according to the order in which they were placed. Two 

 pieces of cloth being put between tl»e instrument and the marble, 

 the order of substances traversed by the heat, was skin, cloth — cloth, 

 marble. After observing the effect, a thin plate of copper was 

 placed between the cloth and the marble ; the fall of temperature 

 was then slower than before : the copper was then placed between 

 the pieces of cloth, and the cooling was as if no copper were 

 present ; then placing the copper beneath the skin of the instru- 

 ment and above the cloth, so that the order was skin, copper, 

 cloth, cloth, marble, the temperature diminished more rapidly 

 than if no copper had been there ; thus the interposition of 

 the metal facilitated the transmission of heat from the skin to 

 the clothiibuti.dimiaisbed.4he l(i'|kiv3iu|s9iQi!Lfrofni^h%f^Ah to the 

 marble.iltof > ff>,'i,. ,.• .- ' k. ,\',ant)[\ vd Ivn ;l(p7 od du^l-^ 



2. fOii) a>3ikthodn9f Measuring inany Chemkal , Actions. — M. 

 Babinet proposes to measure chemical action in cases where 

 gases are generated, by ascertaining the force exerted by 

 the gas evolved. The general cases enumerated are those in 

 which hydrogen, nitrous acid, oxide of azote, carbonic acid, 

 chlorine and sulphurous acid are disengaged. " If the operations 



