96 
cases* several hours should be allowed for it to form. The 
solution should be warmed meanwhile, but must not be 
allowed to boil. The precipitate must be washed till the 
filtrate shows no cloudiness on standing, with nitrate of silver 
when the salts are chlorides ; or, if they are sulphates, till 
chloride of barium gives no cloudiness. The precipitate must 
then be further washed with dilute solution of ammonia, but 
these washings need not be saved. The filter should be 
burnt separately, after the precipitate is cleared from it as 
nearly as possible. After the ignited precipitate is weighed, 
a little strong solution of ammonia should be poured upon it, 
and allowed to stand for awhile, when the ammonia is 
decanted, and supersaturated with acid. If a precipitate 
falls after a time, the tungstate of calcium precipitate should 
(without being removed from the crucible) be allowed to 
stand for some hours with more ammonia — it is then washed 
by decantation, again ignited, and weighed. The ignited 
precipitate should be perfectly white. 
The filtrate, containing the magnesium salt and tungstate 
of sodium, may be at once precipitated by phosphate of sodium 
in the usual way, but if this is done, much washing is required 
to get rid of the little tungstic acid that adheres obstinately 
to the precipitate. It is better, especially when a great excess 
of the re-agent has been used, to first precipitate the tungstic 
acid, by a considerable excess of hydrochloric acid, and boil 
until the precipitate becomes dense and intensely yellow. 
The solution is then filtered, supersaturated with ammonia, 
and the magnesia precipitated in the usual way ; but, even 
in this case, it is better to wash lastly with stronger ammonia 
solution than ordinary. 
