STATE GEOLOGIST. Halk 
to an evaporating dish, preferably platinum, covered with a watch glass 
and 10 cc. hydrochloric acid diluted with about 50 cc. of water added. 
Digestion on the water bath is allowed to go on for about 15 minutes, when 
the substances should be entirely decomposed. The cover glass is then 
removed, washed and the solution evaporated to dryness on the water bath. 
Silica,—The residue without further heating is treated at first with 
5 to 10 ec. strong hydrochloric acid and then as much water as the dish 
will hold. 
The cover is replaced and digestion allowed to go on for 10 minutes 
on the bath, after which the solution is filtered and the separated silica 
washed thoroughly with hot water. The filtrate is again evaporated to 
dryness, the residue without further heating taken up with acid and 
water and the small amount of silica it contains separated on another 
filter paper. The papers containing the residue are transferred to a 
weighed platinum crucible, dried, ignited first over a Bunsen until the 
carbon is completely consumed and finally over a blast for 30 minutes and 
checked by further blasting of Io minutes or to constant weight. The 
silica, if great accuracy is desired, is treated in the crucible with about 
10 cc. hydrofluoric acid and 4 drops of sulphuric acid and evaporated 
over a low flame to complete dryness. The small residue is washed, 
blasted, cooled and weighed. ‘The difference between this weight and 
the weight previously obtained is the amount of silica. Any considerable 
amount of insoluble residue must be fused with sodium carbonate and the 
silica separated as before, the filtrate being added to the main filtrate. 
One evaporation for the dehydration of the silicic acid, however, is only 
required. 
Alumina and Iron.—The filtrate, about 250 cc., from the second evap- 
oration for silica, is made alkaline with ammonium hydroxide and boiled 
10 expel excess of ammonia or until there is but a faint odor of it. The 
precipitated iron and aluminum hydroxides after settling are washed 
once by decantation and slightly on the filter. Setting aside the filtrate 
the precipitate is dissolved in hot hydrochloric acid, the solution passing 
into the beaker in which the precipitation was made. The alumina and 
iron are then reprecipitated by ammonium hydroxide and the second pre- 
cipitate is collected and washed on the same filter used in the first instance. 
The filter must, however, first be moistened with dilute ammonia. The 
filter paper with the precipitate is then placed in a weighed platinum 
crucible, the paper burnt off and the precipitate ignited, and finally 
blasted over the lamp for Io minutes, being careful to prevent reduction. 
After cooling it is weighed as alumina and ferric oxide, which also 
contains the small amounts of titanium, phosphorus and manganese 
present. 
Ferric Oxide—The combined ferric oxide and alumina precipitate 
is fused in a platinum crucible at a very low temperature with about 10 
