216 
PEOEESSOE EOECHHAMMEE ON THE COMPOSITION 
weighed, and calculated as pure chloride of silver. The filter was burnt in a platinum 
crucible, by which the small quantity of chloride of silver was reduced to metallic silver, 
from which the chlorine which had been combined with it was calculated. This suppo- 
sition is correct if the quantity of chloride of silver adhering to the filter is very small. 
2. The determination of the sulphuric acid was likewise made with 1000 grains of 
sea-water, which, after addition of some few drops of nitric acid, was precipitated with 
nitrate of baryta. To try the exactness of the method three portions of sea-water were 
weighed, each of 3000 grains. The result was — 
Sulphate of baryta. 
12-417 
12-316 
12-250 
Mean . . . 12-328 
The greatest difference was 
— 0-078=0-027 sulphuric acid. 
q-0-089 = 0-030 sulphuric acid. 
3. To determine lime and magnesia 2000 grains (in the latter experiments only 
1000 grains) were weighed, and mixed with so much of a solution of sal-ammoniac that 
pure ammonia did not produce any precipitate, then ammonia was added until the 
liquid had a strong smell thereof. It was now precipitated with a solution of the com- 
mon phosphate of soda and ammonia, and filtered when the precipitate had collected 
into a granular powder. The precipitate thus obtained consists of tribasic phosphate 
of lime, and tribasic phosphate of magnesia and ammonia, which was washed with a 
weak solution of ammonia. All the filtered solution and the wash-water was evapo- 
rated in a steam-bath to dryness, and afterwards digested in a tolerably strong solution 
of pure ammonia, by which means there is further obtained a small quantity of the 
phosphates. The dry phosphates of lime and magnesia are heated, and if they are not 
completely white, they are moistened with a few drops of nitric acid, and again heated 
and afterwards weighed. The mass was now dissolved in muriatic acid mixed with 
alcohol until the whole contained 60 per cent, (volume) thereof, mixed with a few drops 
of sulphuric acid, and allowed to stand for twelve hours, when the sulphate of lime is 
collected on a filter, heated and weighed. It contains, besides the sulphate of lime, silica, 
oxide of iron, phosphate of alumina, and sulphate of baryta and strontia, from which 
substances the sulphate of lime is separated by boiling it with a solution containing 
10 per cent, of chloride of sodium, which dissolves the sulphate of lime and leaves the 
other combinations undissolved. The remainder is washed, heated, and its weight 
deducted from that of the sulphate of lime. To try how exact the determination of the 
lime was, I have taken three times 3000 grains of the same water, separated the lime, 
and obtained the following results : — 
