266 A GENERAL FORMULA FOR THE 
convert it into sulphate, by adding sulphuric acid to a slight 
excess, and then exposing to a full red-heat. ‘ihe dry sul- 
phate of lime will remain, 100 grains of which contain 41.5 of 
lime *. red et 
The next step is to precipitate the magnesia. With regard 
to this there is some difficulty, particularly as connected with 
the design of the present formula. The principle on which it 
is founded is, first, to remove all the acids but the muriatic, 
and, secondly, to remove the bases, or otherwise estimate their 
quantities. The lime and the magnesia may be removed by 
precipitation ; the soda cannot. ‘The process, therefore, must 
be so conducted, as to leave it at the end in the state of mu- 
riate of soda. Hence it is necessary either to remove any new 
product introduced in the previous steps of the analysis, or if 
any such remain, to be able to estimate its quantity with pre- 
cision. In decomposing the muriate of lime by oxalate of am- 
monia, muriate of ammonia is substituted, which can be after- 
wards dissipated by heat. The object, therefore, is to decom- 
pose the muriate of magnesia, and remove the magnesia, either 
by some similar method, or, if not, by some other in which the 
muriate substituted can be accurately estimated ; and to attain 
one or other of these conditions, gives rise to the difficulty to 
which I have alluded. 
The 
* The only source of error to which this step of the analysis is liable, is that 
which will arise if more barytes has been used in the first operation, than 
was necessary to precipitate the sulphuric and carbonic acids. It will be 
thrown down in the state of oxalate of barytes, and be converted into carbo- 
nate and sulphate, and thus give the apparent proportion of lime too large. 
This is obviated, of course, by taking care to avoid using an excess of bary- 
tes. To render the operation of the oxalate of ammonia as perfect as possible 
in precipitating the lime, the water should be considerably reduced by evapora- 
tion, taking care to avoid any separation of any of its ingredients. 
ae 
