604 PRINCIPLES OF CHEMISTRY 



is formed with even greater facility under the action of heat in the 

 presence of steam, when HC1 is formed, according to the equation 

 2MgCl 2 + H 2 O = MgOMgCl 2 + 2HC1. 34 bi * 



Calcium (or the metal of lime) and its compounds in many respects 

 present a great resemblance to magnesium compounds, but are also 

 clearly distinguished from them by many properties. 35 In general, 

 calcium stands to magnesium in the same relation as potassium occupies 

 in respect to sodium. Davy obtained metallic calcium, like potassium, 

 as an, amalgam by the action of a galvanic current ; but neither 

 charcoal nor iron decomposes calcium oxide, and even sodium decom- 

 poses calcium chloride 36 with difficulty. But a galvanic current easily 

 decomposes calcium chloride, and metallic sodium somewhat easily 

 decomposes calcium iodide .when heated. As in the case of hydrogen, 

 potassium, and magnesium, the affinity of iodine for caleium is feebler 

 than that of chlorine (and oxygen), and therefore it is not surprising 

 that calcium iodide may be subjected to that decomposition, which the 

 chloride and oxide undergo with difficulty. 37 Metallic calcium is of a 

 yellow colour, and has a considerable lustre, which it preserves in 

 dry air. Its specific gravity is 1'58. Calcium is distinguished by 

 its great ductility ; it melts at a red heat and then burns in the air 

 with a very brilliant flame ; the brilliancy is due to the formation of 

 finely divided infusible calcium oxide. Judging from the fact that 

 calcium in burning gives a very large flame, it is probable that this 



34 bis Jlence MgCl2 may be employed for the preparation of chlorine and hydrochloric 

 acid (Chapters X. and XL). In general magnesium chloride, which is- obtained in large 

 quantities from sea water and "Stassfurt carnallite, may find numerous practical uses. 



55 There are many other methods of separating calcium from magnesium besides that 

 mentioned above (Note 22). Among them it will be sufficient to mention -the behaviour 

 of these bases towards a solution of sugar; hydrated lime is exceedingly soluble in an 

 aqueous solution of sugar, whilst magnesia is but little soluble. All the lime may be 

 extracted from dolomite by burning it, slaking the mixture of oxides thus obtained, and 

 adding a 10 p.c. solution of sugar. Carbonic anhydride precipitates calcium carbonate 

 from this solution. The addition of sugar (molasses) to the lime used for building 

 purposes powerfully increases the binding power of the mortar, as I have myself found. 

 I have been told that in the East (India, Japan) the addition of sugar to cement has long 

 been practised. 



36 Moreover Caron obtained an alloy of calcium and zinc by fusing calcium chlorid* 

 with zinc and sodium. The zinc distilled from this alloy at a white heat, leaving calcium 

 behind (Note 50). 



37 Calcium iodide may be prepared by saturating lime with hydriodic acid. 'It is a very 

 soluble salt (at 20 one part of the salt requires 0"49 part and at 48 0'85 part of water 

 for solution), is deliquescent in the air, and resembles calcium chloride in many respects. 

 It changes but little when evaporated, and like calcium chloride fuses when heated, and 

 therefore all the water may be driven off by heat. If anhydrous calcium iodide be heated 

 with an equivalent quantity of sodium in a closely covered iron crucible, sodium iodide 

 and metallic calcium are formed (Lie*s-Bodart). Dumas advises carrying on this 

 reaction in a closed space under pressure. 



