Dr Daubeny 671 ssparating lAme from Magnesia, 8 IS 
As a further proof that a portion of lime was contained in the 
insoluble residuum, I dissolved it in nitric acid, and found that 
oxalate of ammonia gave a manifest precipitate. 
From the above facts, I think we may conclude, that the ex- 
istence of magnesia tends to facilitate the decomposition of mu- 
riate of lime, although it seems much less. easy to determine in 
this than in the foregoing instances, in what manner the result 
can be influenced by its presence. I know not, indeed, whether 
my readers may not be more disposed to substitute for this, ex- 
planation, the idea of a portion of the calcareous salt being pre- 
served from the action of the water, by the affinity it bears to the 
magnesia ; but be the explanation what it may, the circumstance 
I have alluded to must be considered a serious additional obsta- 
cle to this method of analysis. 
Lime-water appears likewise to throw down magnesia ; but 
it is so difficult to get rid of the carbonic acid which is extricat- 
ed during the solution of the limestone in an acid, and is absorb- 
ed by the water, that we can seldom be sure that this may not 
be the cause of the cloudiness resulting from its addition Be- 
sides this objection to the use of lime-water, there is that of its 
throwing down alumine, which so commonly enters into the com- 
position of magnesian limestones; nor does it appear to separate 
the whole of the magnesia that may be present. 
Fluate of ammonia also appears to me to furnish a method of 
distinguishing the two earths, although my experiments have not 
enabled me to determine, whether this test can be employed 
with advantage as a means of separating them. The above salt, 
indeed, not only has the property long ago attributed to it by 
Scheele, of forming an insoluble salt with lime, but also produces 
the same effect with magnesia ; there being, however, this diffe-. 
rence, that, with the former, the precipitate is from the first inso- 
luble in acids, while, with the latter, it only becomes so by slow 
degrees. 
Hence, if an acid, which exerts a weaker affinity for the two 
bases than the fluoric does, such, for instance, as distilled vine- 
gar, has been previously mixed wdth a solution suspected to con- 
* I believe that carbonic acid is always present in salts obtained from carbo- 
nates, unless the solution has been evaporated to dryness, and redissolved in water 
recently distilled. It is not easy to remove it by simple boiling. 
