94 
was exposed to the same conditions with the re-agent, and the 
reaction in the latter case occurred earlier, at a lower tem- 
perature, and was more distinct. Nevertheless, the fact 
remains that, in a mixed solution of the sulphates of calcium 
and magnesium, the presence of the former may be clearly 
detected up to the proportion of about 1 part in 56,000 of 
fluid containing about 1,000 parts of magnesium salt. 
Rougher experiments made with the corresponding chlorides 
led to similar results. 
(3.) The influence of ammonium salts in obstructing the 
precipitation of calcium in presence of magnesium is very 
marked. A calcium salt, in presence of a very large proportion 
of both magnesium and ammonium salts, cannot be certainly 
recognised except somewhere near ToVcth of the calcium 
salt be present in solution. The influence of free ammonia 
with sulphate of ammonium and sulphate of magnesium, in 
like large proportions, is so great as to only just admit of the 
recognition of the calcium when from Tnhrth to raVrrth is 
present. Nevertheless, enough, and rather more than enough, 
ammoniacal salt may be present to prevent any precipitation 
of magnesium by excess of ammonia, and a moderate excess 
of ammonia may also he present, without sensibly affecting 
the estimation of the lime in a quantitative experiment. 
Chloride of ammonium does not dissolve the precipitate 
when it is once formed. 
The analytical experiments on weighed mixtures of calcium 
and magnesium salts, imperatively necessary in introducing 
a new re-agent, are not yet completed, most of the experi- 
ments of this kind made till now, having been vitiated 
through ignorance of the conditions necessary to ensure 
success. I give, however, the results of one experiment, the 
conditions of which approached more nearly to those I now 
know of as being necessary than the others, reserving the 
series, together with the methods adopted for obtaining pure 
materials to work with, for a second Paper. 
