92 
error, ancl are more apt to fail in less experienced hands, 
than the analytical processes in use for estimating most of 
the other commonly occurring elements. 
In common tungstate of sodium we possess a test for calcium 
which is probably equal in delicacy and in certainty to that 
of chlorine for silver, or of sulphuric acid for barium. 
The action of this test, in a preliminary examination, re- 
quires to he ascertained — 
(1.) With calcium solutions alone. 
(2.) The presence of magnesium. 
(3.) The presence of magnesium and ammonium salts, and 
of these with free ammonia. 
( 1 .) The behaviour of tungstate of sodium with solutions of 
calcium salts . A saturated solution of sulphate of calcium, 
taken at 13° C, remains perfectly clear on addition of an 
equal volume of a saturated solution of tungstate of soda for 
a short time. On warming, when the solution attains the 
temperature of 42° C, it becomes turbid, deposits a film upon 
the containing glass vessel, and soon after a dense precipitate 
falls. To ascertain the limit of the action of the test, the solu- 
tion of sulphate of calcium was successively diluted to various 
degrees, and precipitates obtained, until the solution was so 
dilute that it contained but one part of sulphate of calcium in 
114,000 parts water, A few drops of solution of tungstate of 
sodium were added, the solution warmed, and at 56° C, the 
solution became distinctly opalescent. An experiment was then 
made oh the distilled water used for the dilution, but it gave 
no reaction. It was evident that it was possible to push the 
attenuation much further, and yet get indications of calcium. 
But this proportion (ttAouto) is near the limit at which sulphate 
of calcium may be rendered distinctly visible. A solution of 
chloride of calcium behaves similarly. Sulphate of magnesium 
is not precipitated by tungstate of sodium, unless the solutions 
of the two salts are strong. The experiments were made with 
a solution of pure sulphate of magnesium, of specific gravity 
