594 PRINCII'LKS OF CIIKMISTKY 



magnesium chloride from its aqueous solution. Indeed the mixture 

 with sal-ammoniac (in excess) may be dried (the residue consists of an 

 anhydrous double salt, Mg( '1.,,1'X 1 1 ,( '] ) and then ignited (4G()), when 

 the sal-ammoniac is converted into vapour and a fused mass of 

 anhydrous magnesium chloride remains behind. The anhydrous chloride 

 evolves a very considerable amount of heat on the addition of water, 

 which shows the great atlinity the salt has for water/" Anhydrous 

 magnesium chloride is not only obtained bv the above method, but is 

 also formed by the direct combination of chlorine and magnesium, and 

 by the action of chlorine on magnesium oxide, oxvgen being evolved : 

 this proceeds still more easily In/ In'itfni<j HKI</H' *n> />/?// <//(//'<<>(// ni n 

 *f, -,<//,, ,,/' !/,/<>,'! /f. when the charcoal serves to take up the oxygen. 

 Tin-- latter method is also employed for the preparation of chlorides 

 which an 1 formed in an anhydrous form with --till greater difficulty 

 than magnesium chloride. Anhydrous magnesium chloride forms a 

 eolotirles>, transparent mass, composed of flexible crystalline plates 

 of a pearlv lustre. It fuses at low red heat (7<>S' r ) into a colourless 

 lifjiiid. remains unchanged in a dry state, but under the action of 

 moisture is partially decomposed even at the ordinary temperature, 

 with formation of hydrochloric acid. 



('</!' i a in compounds in many respects present a great nesem- 

 blaiice to magnesium compounds, but are also clearly distinguished 

 from them bv manv properties. 3 ' 1 In general calcium stands to 

 magnesium in the same relation as potassium occupies in respect 

 to -.odium. I)avv obtained metallic calcium, like potassium, as an 

 amalgam hv the action of a galvanic current : but neither charcoal nor 

 iron decomposes calcium oxide, and even sodium decomposes calcium 

 chloride 3 '' \\ith difficulty. Hut a galvanic current easily decomposes 

 calcium chloride, and metallic sodium somewhat easily decomposes 

 calcium iodide when healed. As in the case of hydrogen, potassium, 



n of M'j( '] . u itli '.I I O evolves I'.IiOOO nilories, 

 heat units. 



i I 1 , it iii'j ca lei n in t'rolll ma;j iie-inm lioides that 

 t Will In- >llf'licient to nielli ioll the l.eha violir 



ivdvated //'//// ! exceedingly *<ilnl,li- in an 

 -ia is little sollllile. All the lilile IllilY lie e\- 

 lln ill lure of i ixides lluis olitained. and 

 Ciirlionie anhvdride precipitates calcium carhonate 



' , l-.la r. (ri the lime I1SI-<1 fill' l.llildill- 



a e- t he liindimj |n i\\ er of the innrtar, as I ha\ e my-elf t mi IK I. 

 In Ka>! India, -laiian i 1 he addil ion ,,| u-,ir |o cement has loir_ r 



