95 
Taken, Found. 
Magnesia 0-3097 grms. 0-3120 
Carbonate of calcium... 0-0043 0-0042 
The weighed quantities of carbonate of calcium and of mag- 
nesium were dissolved in a slight excess of hydrochloric acid ; 
neutralised carefully by ammonia, precipitated by tungstate 
of sodium, and then the filtrate, with the usual precautions, 
by common phosphate of sodium. The excess in the weight of 
pyro-phosphate of magnesium, led to the suspicion that some 
tungstic acid had been carried down ; a suspicion amply 
confirmed by the colouration obtained from the solution of 
the ignited precipitate in dilute hydrochloric acid when 
treated with tin. 
A little in anticipation of my intended future paper upon 
the subject, I now add such details respecting the manipula- 
tion required in separating lime from magnesia by tungstate 
of sodium as my experience has shown to be necessary. It is 
convenient to have the solution of the magnesium and 
calcium salts made somewhat alkaline by ammonia, but a 
very large quantity of this, as well as of ammoniacal salt, is, 
as we have seen, to be avoided. The beaker in which the 
precipitation is to be effected should, while perfectly dry and 
warm, be rubbed within by chamois leather on which a drop 
or two of fine oil (such as is used for oiling balances) has 
been put. If this precaution be not taken, it will be found im- 
possible to detach the precipitate of tungstate of calcium from 
the sides and bottom of the vessel. A considerable excess of 
the re-agent is not necessary ; but, if it occur, is not material. 
If, on addition of the re-agent, a white, floculent precipitate 
forms immediately, it is well to add a few (drops of ammonia, 
when the floculent precipitate will re-dissolve, but if it does 
not re-dissolve, after warming, there is some other element 
present, which, if ordinary Epsom salts are used will probably 
be manganese. The tungstate of calcium precipitate is very 
dense ; it forms slowly in very dilute solutions, and, in all 
