SOT 
Chroma t of Lead . 
be so faintly coloured 5 that a further continuance of the boiling will 
be a waste of time ; then the remainder, which consists of oxyded 
iron, may be thrown away, and the kettle rinsed clean. A part of 
the liquid is now to be introduced into the kettle, and briskly boil- 
ed, supplying the waste as it boils away, until the whole is intro- 
duced therein ; it should then be concentrated until it is nearly at 
the point of crystallizing when cold ; when it may be thrown on a 
niter, to separate the iron which may remain suspended therein* 
together with the magnesia which will have precipitated* 
On gradually adding nitric acid to the filtered liquid, a precipi- 
tate will appear, which is the earths held in solution by the potash 
of decomposed nitre, and disengaged by the acid combining with 
the alkali ; but attention must be paid not to add the acid in excess, 
otherwise the precipitate will be immediately re-dissolved ; the 
better way will be to add less acid than is deemed necessary, to 
separate by filtration the precipitate which may appear, and to 
the filtered liquid add fresh acid, then filter again and repeat the 
process as often as a precipitate falls; by that cautious proceed- 
ing the separation of the earths may be considerably approximated, 
but not entirely effected. 
Nitric acid is now to be added until the solution tastes sensibly 
sour ; it is then to be boiled in a glass vessel, and whilst boiling a 
few drops of acid are to be added as long as an effervescence or 
even globules of air appear to rise from below the surface of the 
liquid, on each addition of nitric acid ; when they cease, the solu- 
tion must be briskly boiled for fifteen or twenty minutes, which will 
completely expel the carbonic acid -which may remain. 
Into the above solution, either hot or cold, a solution of nitrate 
or acetate of lead is to be poured so long as a precipitate appears : 
or the acetate , if clean 3 may be added in 'fiowdet or linnfis^ which 
I think preferable, as we thereby avoid the bulky solution which is 
so very inconvenient where capacious glass vessels are difficult 
to procure. When the precipitation is completed, it should be 
thrown on a filter and well washed, by filling the filter fifteen or 
twenty times with boiling distilled water; the water being suffer- 
ed to run entirely off, before the filter is again filled. As the beau- 
ty of the colour and the property of drying quickly will greatly 
depend on its being well washed. It may be interesting to add, 
that I have found strong boiling of river water a good substitute 
for distilled ; the water was boiled for half an hour in an open ves- 
sel, then suffered to cool, it deposited a considerable sediment of 
vegetable matter, and in winter, some carbonate of lime, which 
