On the Natural Groupings of the Elements. 481 



The atomic heat of sodium and potassium is double that of 

 most of the metals. 



Group VI. Calcium, Strontium, Barium. 



All chemists are agreed in their association of these three 

 metals into one group, which, however, is usually made to in- 

 clude magnesium also. The principal points of analogy are, the 

 relation of the atomic weights, that of strontium being interme- 

 diate between the other two. 



Ca = 20 132-3 , . , 



Sr = 43-8 -3- = 44-l 



Ba = 68-5 



Sum 132-3 Mean diflference =24. 



The saline atomic volumes of the three metals, as estimated 

 by Kopp, present us with a similar sequence : — 



Ca = 60 311 _ 



Sr = 108 ~3~~ '^ 



Ba = 143 



Sum 311 



The three metals are soft, readily fusible, decompose water at 

 all temperatures, are easily combustible, and oxidize rapidly even 

 in dry air. Each metal forms only one class of salts. The hy- 

 drates, sulphides, sulphydrates, chlorides, and nitrates are soluble 

 in water ; the carbonates, sulphates, borates, and phosphates are 

 insoluble. The carbonates are all decomposed at a red heat. 

 Of the three sulphates, that of calcium is the most soluble, then 

 that of strontium, then that of barium. The nitrate and chlo- 

 ride of calcium are very deliquescent, those of sti-ontium less so, 

 those of barium not at all so. The corresponding salts are for 

 the most part isomorphous. Thus BaCl . H^O is isomorphous 

 with CaCl . H^O, and SrC1.3H20 with CaCl.SlPO. Witherite is 

 isomorphous with calc-spar, strontianite with arragonite. Heavy 

 spar, celestine and anhydrite, all crystallize in the right prismatic 

 system, &c. 



The metals of the fifth and sixth groups arc the only ones 

 that form decidedly soluble hydrates and sulphides. The so- 

 luble sulphates of lithium and sodium are associated with the in- 

 soluble sulphates of strontium and barium by means of the spa- 

 ringly soluble sulphates of potassium and calcium. Of the three 

 alkaline metals, however, lithium seems to approximate most 

 to those of the alkaline earths. A curious isomorphism of cal- 

 cium with potassium and sodium is exhibited between the nitrates 

 and carbonates. We have 



k 



