52 ON THE SOLUBILITY OP SOME PRECIPITATES. 
VIII. Solubility of pure Magnesia in Water.* — Perfect- 
ly pure crystallized sulphate of magnesia was dissolved in 
water, the solution precipitated with carbonate and caustic 
ammonia, the precipitate most carefully washed (it still con- 
tained nevertheless a perceptible trace of sulphuric acid ;) 
it was dissolved in pure nitric acid, avoiding an excess of 
acid, again precipitated with carbonate and pure ammonia, 
and the precipitate most carefully edulcorated. The per- 
fectly pure basic carbonate of magnesia thus obtained was 
ignited in the platinum crucible until its weight remained 
constant, then digested with distilled water (which left on 
evaporation not a trace of fixed residue, and was likewise 
perfectly free from chlorine) for 24 hours in the cold, being 
frequently agitated. 1 part of pure magnesia was found, 
on an average of three experiments, to dissolve in 55368 
parts cold water. This solution of magnesia has a faint but 
distinctly alkaline reaction, which may easily be detected 
by means of slightly reddened litmus paper; it is not ren- 
dered turbid by alkaline carbonates either in the cold or 
on boiling; it likewise remains clear with phosphate of soda, 
but if ammonia be added it becomes turbid after slight agi- 
tation, and soon deposits a distinct precipitate of basic phos- 
phate of ammonia and magnesia. 
Pure magnesia, boiled with water, yields a solution 
which behaves in every respect like that prepared in the 
cold. 
IX. Solubility of the Carbonate of Lead. — The author 
finds that 1 part requires 50551 parts of pure water at the 
ordinary temperature for solution; this solution is not in the 
slightest degree coloured by sulphuretted hydrogen. 
In water which contained a little acetate of ammonia, 
and also carbonate and pure ammonia, 1 part of the salt dis- 
solves 23450 parts ; the solution was slightly coloured by 
* The very different results formerly obtained are undoubtedly 
owing to an imperfectly pure magnesia having been employed in the 
experiments. 
