FIXED ALKALIES AND ALKALINE EARTHS. 



and there remained undissolved 3 grains of pure 

 magnesia. Now, if we suppose the 1O3 grains 

 which dissolved, to have been previously in the 

 state of chloride of magnesium, they must have 

 consisted of 



Magnesium 2'575 

 Chlorine 7'725 



10-300 



And 2'575 grains of magnesium are equivalent 

 to 4*29 grains of magnesia. Now, 4*29 + 3*= 

 7*29, which is the amount of the magnesia ori- 

 ginally present in the carbonate employed. It 

 would appear that in this experiment a chloride 

 of magnesium was obtained. 

 Atom of Jt j s obvious, if the preceding experiment 



magnesi- 

 um, deserves any confidence, that magnesia is a com- 

 pound of 



1 atom magnesium 1-5 

 1 atom oxygen 3 -0 



2-5 



And this is corroborated by the following ex- 

 periment originally made by Sir H. Davy. 

 When magnesia is heated, and a current of chlo- 

 rine gas passed over it, oxygen is given out, and 

 the magnesia is converted into chloride of mag- 

 nesium. Now, for every volume of chlorine 

 absorbed, half a volume of oxygen gas is given 

 out. This shows that magnesia contains only 1 



