1817.] Thorina; a new Earth. 453 
‘its deeper colour is owing to the presence of a greater proportion of 
manganese. 
The rarest variety is that which is amorphous, and presents no 
marks of crystallization. Some of the experiments made upon it 
~deserve to be stated here, though they cannot be considered as ex- 
hibiting an exact analysis: 
A. Forty-eight parts of it being reduced to an impalpable powder, 
and calcined in a red heat, were submitted to the action of concen- 
trated sulphuric acid, which occasioned the separation of the fluoric 
acid gas, and converted the mass into a semiliquid substance of a 
tine deep brown colour. After two hours’ digestion it was brought 
in contact with a little water, which occasioned a slight muddiness. 
The yellow liquid was. decanted off, and mixed with hot water; 
which occasioned still greater opacity. The precipitate, being col- 
lected on the same filter as the undissolved portion, and béing 
washed and heated to redness, weighed 9°6 parts. 
B. The liquid was mixed with sulphate of potash till the whole 
of the cerium separated. When properly washed and dried, the 
oxide of cerium obtained weighed 26:3 parts, 
C. The solution was then treated with ammonia. The resulting 
precipitate weighed, after calcination, 1-525 parts; and I found by 
an examination which I conceive it to be unnecessary to state sepa- 
rately, a mixture of yttria, alumina, oxide of manganese, and 
silica. 
D. The 9°6 parts that had not been dissolved by sulphuric acid 
were digested at the temperature of boiling water in muriatic acid, 
which dissolved them with the exception of 2:5 parts, which were 
silica mixed with a trace of proto-fluate of cerium. 
E. The muriatic solution was mixed with caustic ammonia. The 
precipitate, being thrown upon a filter, was well washed, and dis- 
solved while still moist in nitric acid; and this solution was left to 
evaporate spontaneously in a warm place. It produced a gummy 
mass, deliquescing in the air, which, being dissolved in a greater 
quantity of water, and boiled, let fall a white gelatinous precipitate, 
which was collected on the filter. It weighed three parts. Caustic 
ammonia, being mixed with the remaining solution, precipitated, 
oxide of cerium, which still contained a portion of the earth preci-~ 
pitated by boiling. I shall describe below the experiments made on 
this earth. 
The analysis, then, had assigned oxide of cerium as the principal 
substance, and had given the total quantity of 37-4 of solid matter. 
The loss, amounting to 10°6, greatly exceeds the quantity of fluoric 
acid which was requisite to saturate the different bases. This excess 
of loss is no doubt owing to the fluoric acid having carried off with 
it a portion of silica, which in all probability was only mechanically 
mixed, as it is in the minerals which I shall mention immediately, 
Double Fluate of Cerium and Yitria.—There is an earthy mineral 
found at Finbo which is much more common than the neutral 
fluates and subfluates of cerium; but its size seldom exceeds that of 
