MAGNESIUM. 503 



protoxide of iron only, and not with a salt of the peroxide. By 

 means of a glass stirrer, a white stoneware plate is spotted over 

 with small drops of the prussiate. A drop of the iron solution 

 is mixed with one of these,, after every addition of chloride of 

 lime,, and the additions continued, so long as a deep blue 

 precipitate is produced. The liquid may continue to be 

 coloured green by the iron salt, but that is of no moment. 

 The richer the specimen of chloride of lime is in chlorine, 'the 

 fewer measures of its solution are required to peroxidise the 

 iron, the number of measures containing 10 grains of chlorine 

 always producing that effect. The quantity of chlorine in the 

 fifty grains of bleaching powder is now known, being ascer- 

 tained by the proportion, as m measures (the number poured 

 out of the alkalimeter) is to 10 grains of chlorine,, so 100 is to 

 the total grains of chlorine. In a particular experiment the 78 

 grains of sulphate of iron required 72 measures of the bleaching 

 solution. Hence, as 72 is to 10, so 100 is to 13.89 chlorine in 

 50 grains of the chloride of lime. The quantity of chlorine in 

 100 grains of the chloride, or the per centage of chlorine, is ob- 

 tained by doubling that number, and was therefore in this in- 

 stance 27-78 per cent, or 28 per cent. The arithmetical process 

 may always be reduced to that of dividing 2000 by the number 

 of measures poured from the alkalimeter ; thus in the last 

 example 



SECTION VII. 



MAGNESIUM. 

 Eg. 158.3, or 12.69; Mg. 



To obtain magnesium, sodium in a test-tube of hard glass is 

 covered by fragments of anhydrous chloride of magnesium, and 

 heated to redness by a lamp. The alkaline metal unites with 

 chlorine, with strong ignition. After extracting the chloride of 

 sodium by means of water, the magnesium remains in little 

 globules, which may be re-united, by fusing them under a 

 stratum of chloride of potassium at a moderate red heat. 



Magnesium has the colour and lustre of silver; it is n alleable, 



