174 /.*. Bw>^en-^raJonn»4rir In r,.ti;/aHons. 



tastened on a heavy iron stand by means of a vice, wliose jaws 

 surround tightly the lower pai't oi' the iron head-piece d. 



The amount of heat vvhicli a body evolves in cooling from a 

 given temperature to 0° C, is determined by dropping it into 

 the water in the vessel a and thereupon closing the vessel at ri 

 with a cork, to prevent any circulation of air. If the problem 

 be the relative measurements of quantities of heat, as in the 

 ( I ctenni nation of specific heats, then the standai-d of (•oin[)ajis(»u 

 is directly afforded by the number of scale-divisions which 

 tlie mercury thread has passed o!i its retreat. If tiie i'eadiiig> 

 lav rendered in an absolute measure, as Ibr instance, in grams of 

 melted ice, or in units of heat, as the unit in tin; following pages, 

 (always that quantity of heat being understood which one gram ol 

 water at 0'^ C. absorbs in order to raise its temperature to 1° C), 

 then it is only necessary to multiply the readings on the scale 

 with a constant which results from the following consideration. 



A mercury thread measured in the scale tube, which has the 

 temperature "t° and occupies T divisions of the tube after being 

 corrected by the calibration table, weighs g grams. Let further 

 the specific gravity of mercury at 0° C. be S,, its coefficient of 

 expansion a, then is the volunie u of a corrected division on the 



~ s/r • 



For the instrument which I used, the values were : 



g= 0-5326 a= 0-0001815 ? = 9° C. 



S,= 13-596 T = . 507-4 



and therefore 



V = 0-00007733 c.c. (1) 



If the specific gravity of ice at 0° C. be denoted by S„ thespe^ 

 cific gravity of water at the same temperature by S;^, the weigh 

 of melted ice expressed in grams, which corresponds to tne 

 volume V, that is, to one scale division with p, then is 

 ^ P 



With regard to the specific oravit v of u-o w- iui\ e many obser 

 vations. The following comparisoii shows how little they agre« 

 among themselves. For S, 



Thomson found 0-920 PlUeker and I Q.920 



Heinrich, 0-905 Geissler, f 



Osan, 0-927 Kopp, *^■^^^^.x.] 



Rover and D,iTnn« n-oso Y^Jn^u■ 0-922 (ma^^ 



