352 Prof. J. W. Mailet on the Atomic Weight of Lithium. 
were chosen for comparison with lithia because the last-named 
base seems in most of its relations to hold an intermediate place 
between the former two, with which it is closely allied. Chlorid 
of barium was also prepared with all the precautions needed to 
ensure its purity, precipitated twice from its aqueous solution by 
alcohol, and recrystallized three or four times. It was at last 
obtained as a fine crystalline powder by stirring the hot satura- 
solution as it cooled, and this powder was allowed to dry 
spontaneously in the air at a temperature of about 80° F. Thus 
prepared, the salt—as Marignac has shown—is not altered in 
weight by further exposure to air, its theoretical composition is 
BaCl+2HO, the precise amount of water actually present was 
probably a little greater, owing to the mode of drying, but was 
unimportant under the conditions of experiment adopted. 
For each of the six weighed portions of sulphates mentioned 
above, the quantity of chlorid of barium needed for exact pre- 
cipitation was calculated, assuming the equivalent of sodium 
= of magnesium =12, that of lithium =7, and that of 
barium =68°6, and considering the chlorid of barium as con- 
taining strictly two. atoms of water. Six portions of the last- 
named salt were weighed out (at the same time), each less than 
the amount calculated by one or two centigrams. Each was dis- 
solved in 200 cubic centimetres of hot water, and added to its 
corresponding portion of sulphate, likewise dissolved in 200 cub. 
centim. of hot water. The fluid and precipitate in the six 
beakers were well stirred, and left to settle. 
ally taken. At first it was easy to observe the formation of a 
