1.55 
on, allowing for every hundred grains two drachms 
or one hundred and twenty grains of acid. 
The substance remaining after the action of the 
acid may be considered as siliceous; and it must 
be separated, and its weight ascertained, after 
washing and drying in the usual manner. 
The alumina and the oxide of iron and manga- 
nesum, if any exist, are all dissolved by the sul- 
phuric acid : they may be separated by succinate 
of ammonia, added to excess ; which throws down 
the oxide of iron, and by soap lye, which will 
dissolve the alumina, but not the oxide of manga- 
nesum ; the weights of the oxides ascertained after 
they have been heated to redness will denote their 
quantities. 
Should any magnesia and lime have escaped 
solution in the muriatic acid, they will be found 
in the sulphuric acid ; this, however, is rarely the 
case; but the process for detecting them, and 
ascertaining their quantities, is the same in both 
instances. 
The method of analysis by sulphuric acid is 
sufficiently precise for all usual experiments ; but 
if very great accuracy be an object, dry carbonate 
of potassa must be employed as the agent, and the 
residuum of the incineration (6) must be heated 
red for half an hour, with four times its weight of 
this substance, in a crucible of silver, or of well- 
baked porcelain. The mass obtained must be 
dissolved in muriatic acid, and the solution eva- 
porated till it is nearly solid ; distilled water must 
then be added, by which the oxide of iron and all 
the earths, except silica, will be dissolved in com- 
