198 PROFESSOR HEDDLE ON .THE MINERALOGY OF SCOTLAND. 
trials ; the fusions, though in an unusually close crucible, having been found to 
be impregnated throughout with copper. 
The acidified solution of the “glass” was evaporated to absolute dryness, 
with granulation, in a water-bath, which kept its beakers at the average 
temperature of 186° Fahr. In the case either of an unusually large quantity 
of material, or an unusually large proportion of alkalies, the saline mass from 
the first granulation was redissolved in water and regranulated. 
After the separation of the main silica, the iron was peroxidised by nitric 
acid, it and the alumina thrown down as basic acetates, filtered off hot, and 
washed with sodium acetate. The precipitate was redissolved in hydrochloric 
acid, and evaporated to dryness with granulation, to separate the hitherto soluble 
silica. 
The acid solution of the iron and alumina, now free from silica, was made up 
to the bulk of 250 c.c.; 100 of these were employed for determining the total 
ferric oxide and alumina combined; measured quantities of the remainder being, 
after reduction with zinc, used for the ascertaining the total iron, by perman- 
ganate of potassium. This calculated to ferric oxide, and as such deducted 
from the total ferric oxide and aluminia, gives finally the amount of alumina. 
In the filtrate from the basic acetates, the manganese was thrown down by 
bromine water. The lime and magnesia were determined as usual; the ammo- 
nium oxalate precipitate being invariably redissolved, and the lime reprecipi-— 
tated ; in the case of substances with large amounts of magnesia, it was found 
necessary to repeat the resolution and precipitation. . 
3. Estimation of the Ferrous Oxide.—About *3 grammes of the finely 
powdered mineral were intimately mixed with a considerably larger amount of 
colourless and pure fluorspar, in a platinum crucible, the lid of which has a 
small central orifice,—through this orifice sulphuric acid is added drop 
by drop. The crucible fits into and fills up an opening in the bottom of a 
copper chamber, which stands over one of the holes of the water-bath ; over 
the crucible, but within the chamber, there stands a three-necked WouLrrs 
bottle, from which the bottom has been removed by grinding. Through a — 
recurved funnel tube in the central neck more acid may be added if neces- 
sary; through one of the lateral necks a continuous current of carbonic acid is 
conveyed into the chamber ;—the tube in the third neck gives exit to this current. 
With sulphuric acid, the decomposition of a silicate is complete in about 
three minutes, and the whole fluosilicic and hydrofluoric acid driven off in less 
than twenty. With hydrochloric acid, the action is neither so speedy nor so 
certain. 
After the dissipation of the fluorine acids, the contents of the crucible are 
washed into about five cubic inches of recently boiled water, cooled in vacuo; 
and the iron, in the state of ferrous oxide, titrated by permanganate. The 

