Mixter — Thermochemistry and the Periodic Laiv. 525 



The fundamental values of the thermochemistry of the 

 calcium, strontium and barium compounds are the heats of 

 reaction of the metals with water or hydrochloric acid. For 

 calcium we have Ca + 2HC1 = 129*0 Cal. (Guntz & Bassett) 

 and Ca + Aq = 94*1 Cal. (Moisson). These data give re- 

 spectively Ca + O = 151*4 and 145*0 Cal. For strontium, 



Fig. 2. 



•2R+S+4-0 



Fig. 2. Diagram of Group I. The heats of formation of the oxides and 

 chlorides of lithium, potassium, rubidium and caesium are connected by 

 heavy lines, of the other elements of the group by light lines. 



Sr 4- 2HC1 = 117-05 (T) and 128*0 Cal. (Guntz & Koederer). 

 Using Thomsen's values for the heat of solution of SrO, etc., 

 we derive Sr + O = 128*4 (T) and 139*4 (G. & R.). For 

 barium we have only Guntz's result, which is Ba + Aq = 92*5 

 Cal., which gives with Thomsen's values 126*4 Cal. for 

 Ba + O. deForcrand by dissolving SrO,H 2 and BaO,H s O 

 in hydrochloric acid and combining his results with those of 

 Guntz found that Sr + O = 138*6 Cal. and in more recent 



