NEW LAW IN THERMOCHEMISTRY 



33 



It will be observed that the value for bivalent calcium, which 

 liberates twice as much hydrogen and combines with twice as 

 much hj'droxyl as the alkaline metals proper, gives double the 

 usual quantity of heat. Similar figures, comparable with these, 

 are given by De Forcrand,^ who studied the thermal phenomena 

 attendinor the solution of the same metals in different alcohols. 

 I cite his data below : 



Here again the fundamental identity is manifested, although it 

 is probable that in the different solvents the products of solution 

 were differently, that is, more or less completely ionized. This 

 consideration alone is enough to account for most of the diver- 

 gencies. All of these reactions are analogous, and the figures 

 given are nearly enough alike to illustrate the principle which 

 I have enunciated. So far, however, we cannot analyze the 

 measurements, and disentangle the separate factors of which 

 they are the algebraic sums. 



Another illustration of the difficulties which arise in the inter- 

 pretation of thermochemical measurements, is offered by Thom- 

 sen's ^ data for the apparent heats of formation, in aqueous solu- 

 tion, of numerous metallic halides. His figures for the salts of 

 the alkaline and earthy metals are as follows : 



Lithium 



Sodium 



Potassium ... 

 Magnesium. 



Calcium 



Strontium ... 

 Barium 



Chloride. 



102250 

 96510 

 101170 

 186930 

 187230 

 195690 

 196810 



Bromide. 



91310 

 85580 

 90230 



165360 

 173810 

 174940 



Iodide. 



76100 

 70300 

 75020 



134940 

 143460 

 144520 



These quantities, which were determined by indirect methods, 

 are supposed to start from solid metal, solid iodine, liquid bro- 



^Compt. Rend., vol. loi, p. 31S. 



2 Data scattered throughout yol. 3 of Thermochemische Untersuchungen. 

 Proc. Wash. Acad. Sci., February, 1903. 



