Additional Observations on the Effects of Magnesia. 347 
why the infusion is stronger, if only a small quantity of 
boiling water be first used, and more be added some time 
afterwards. If we consider that only the water immediately 
in contact with the herb can act upon it, and that it cools 
very rapidly, especially in black earthen-ware, it is clear that 
the effect will be greater where the heat is kept up by addi- 
tions of boiling water, than where the vessel is filled at 
once, and the fluid suffered gradually to cool. 
When the infusion has once been completed, it is found 
that any further addition of the herb, only affords a very 
small increase in the strength, the water having cooled 
much below the boiling point, and consequently acting 
very slightly. 
Some may be inclined to consider these remarks as too 
trifling ; but they should remember, that it is by the appli- 
cation of philosophic principles to the ordinary and even 
trivial occurrences of life, that science diffuses her benefits, 
and perfects her claim to the gratitude of mankind. 
LVIIT. Additional Observations on the Effects of AZagnesia 
in preventing an increased Formation of Uric Acid ; with 
* Remarks on the Influence of Acids upon the Composition 
of the Urine. By Wittiam Tuomas Branpbe, Esq. 
F.R.S. Prof. Chem. R.I.* 
i a paper which I bad the honour of laying before this 
Society, about three years ago, and which is published in 
the Philosophical Transactionst, some cases are related, 
illustrating the effects of magnesia in preventing an in- 
creased formation of uric acid, and some experiments are 
detailed, instituted with a view to discover its mode of 
action. 
Since that period many opportunities have occurred both 
to Sir Everard Home and myself, of confirming its efficacy 
upon a more extended scale, and of ascertaining the effi- 
cient treatment of those cases in which magnesia is inef- 
fectual, and in which it has even been found to aggravate 
the complaint. 
To bring forward additional evidence in favour of the 
use of magnesia, and to distinguish the cases in which its 
use is indicated, from those where it is improper or hurtful, 
are the principal objects of the present communication, and 
will be considered in the two following sectious. 
oO 
j=] 
* From the Philosophical Transactions for 1813, part ii. 
+ For 1810, p. 106. 
SEc+ 
