272 ON DIFFERENT KINDS OF MAGNESIA, ETC. 
circumstances, and to follow a natural law in chemistry, 
the stronger acid combined with the stronger bases, and 
vice versa. 
From the above facts, some important hints might be af- 
forded to analytical chemistry, for it will be at once seen 
that the presence of any of the alkaline salts in a solution 
from which it might be wished to precipitate lead in the 
form of sulphate, would affect the accuracy of the result. 
What is true of the sulphate of lead may be found also true 
for other insoluble salts. Moreover, this shows the impor- 
tance, in the analysis of mineral waters for instance, of 
weighing well the relative strength of the various acids and 
bases therein found, in order to ascertain what salts are 
present, and not to be contented with evaporating the 
# water to dryness, and considering such salts as remain to 
be those existing in the water, for many of them may be 
formed during the evaporation. It is not at all improbable 
that before many years the examination of mineral waters 
will be based as much upon calculation as upon analysis, 
the former, of course, being guided by the latter, and by 
certain laws not yet developed. 
Ibid, from Jim. Journ. of Science and Arts. 
ART. LIX. — ON THE DIFFERENT KINDS OF CALCINED 
MAGNESIA EMPLOYED IN MEDICINE. 
By M. Mialhe. 
It is in consequence of some remarks published concern- 
ing an advantageous formula for employ ing magnesia as 
a purgative, which I last year inserted in the Bulletin de 
Therapeutique, that I have been led to make the chemical 
