218 
PROFESSOR FORC1IHAMMER OjST THE COMPOSITION 
its weight is one-half of the quantity of sulphate of baryta, obtained from an equal 
quantity of the same sea-water in a previous experiment for the determination of sul- 
phuric acid. All is now evaporated to dryness and dissolved in alcohol of 60 per cent., 
which leaves the sulphate of lime and dissolves all the chlorides ; so that the solution 
is quite free from sulphuric acid. It is now a third time evaporated with a sufficient 
quantity of chloride of platinum. Alcohol of 60 per cent, leaves the chloride of plati- 
num and potassium, which might be weighed, and the quantity of chloride of potassium 
calculated from it ; but as it is most difficult in a laboratory where there is constantly 
work going on to avoid the absorption of the vapours of ammonia by evaporating 
liquors, I prefer heating the double chloride to a dull red heat, and assisting the 
decomposition of the chloride of platinum by throwing small pieces of carbonate of 
ammonia in the crucible. When all the chloride of platinum is decomposed, the crucible 
is weighed, the chloride of potassium is extracted by alcohol of 60 per cent., and the 
remainder weighed again. This method has the advantage, that even if a small quan- 
tity of gypsum should have accompanied the double chloride, it will have no influence 
upon the determination of the chloride of potassium. When I do not want to 
determine the insoluble remainder, I evaporate the sea-water with a sufficient quantity 
of chloride of calcium, and thus leave out one evaporation and solution. 
In the few cases where I have tried to determine the different substances which in 
this chapter I have called silica, &c., I have used the following method. The filter 
upon which the remainder is collected and washed is burnt in a platinum crucible, 
evaporated with some drops of muriatic acid, and dissolved in water. What remains is 
silica, often coloured by a little oxide of iron, and mixed with a small quantity of 
sulphates of baryta and strontia. It is evaporated with fluoric acid and a drop of 
sulphuric acid to get rid of the silica. What remains after evaporation and heating 
is sulphate of baryta, of strontia, and oxide of iron. The solution in muriatic acid is 
precipitated by ammonia, and the precipitate is noted as phosphate of lime, but con- 
tains besides a little fluoride of calcium. The remaining liquid contains a little lime, 
which I precipitate with oxalate of ammonia, and suppose to have been in the sea-water 
as carbonate of lime dissolved by carbonic acid. In the water of the great ocean there 
occurs only a very small quantity of carbonate of lime, but near the shores, in the 
bays and inlets, and principally in the mouth of the great rivers, its quantity increases 
with the quantity of fresh water from the land. If the sulphates of the sea-water 
are decomposed to sulphurets, there is always precipitated a larger quantity of carbonate 
of lime, but that is the result of the decomposition, and its carbonic acid is owing to 
the organic substances which are oxidized by the oxygen of the sulphates. 
I have never tried to ascertain the nature and quantity of the gases which occur in 
sea-water, because the collection of sea-water for that purpose would require quite 
different precautions from those which were necessary for the water intended for the 
analysis of its solid contents. 
It might seem that the relative quantity of salt might be inexact, because water might 
