305 



of barites, which is equivalent to 4.43 grains of chloride of ba- 

 rium. I must, therefore, have used 4.43 grains of chloride of 

 barium more than was necessary to precipitate all the sulphu- 

 ric acid from the sulphate of magnesia, so that 104.17 grains 

 of chloride of barium is sufficient to precipitate all the sulphu- 

 ric acid from 60.05 of sulphate of magnesia, or 104 grains of 

 chloride of barium would precipitate the sulphuric acid from 

 59.95 grains of sulphate of magnesia. This makes the atomic 

 weight of magnesia 19.95, or quam proxime, 20. 

 My final experiment was as follows : — 

 I dissolved 41.44 grains of pure magnesia in sulphuric acid, 

 and having evaporated the solution to dryness, and exposed the 

 residuum to a low red heat for about an hour and a half, the 

 resulting sulphate of magnesia was found to weigh 124.40 

 grains. 41.44 grains, therefore, of magnesia, and 82.96 of sul- 

 phuric acid, form 124.40 grains of sulphate of magnesia; or 

 40 grains of sulphuric acid and 19.98 grains of magnesia form 

 59.98 grains of sulphate of magnesia, which gives 19.98 as the 

 atomic weight of magnesia. If 12.7 was the atomic weight of 

 magnesium, 41.44 grains of magnesia would have given 121.51 

 grains of sulphate of magnesia, and not 124.40 grains. 



N.B. — The following were the atomic weights used in 

 calculating the experiments just described : — 



SO 3 = 40 



CI = 35.5 



Ba =68.5 



