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 guam prozxime, 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 :— 
S O; = 40 
Cl =35.5 
Ba =68.5 
