REPORT ON CHEMISTRY. 
475 
compound is a double silicate of alumina and soda, coloured by 
combining with sulphuret of sodium. He precipitates alum 
by caustic ammonia, washes and dries the subsulphate, and 
estimates the amount of water it contains. In like manner he 
precipitates silica from its solution in an alkali, washes and 
dries without heating to redness. The silica is dissolved in 
a concentrated solution of caustic soda to saturation, and for 
every seventy-two parts thus dissolved, seventy of the alumina 
are added, each calculated in the anhydrous state, and the 
whole evaporated to the state of a moist powder. Two parts 
of sulphur and one of dry carbonate of soda are now fused 
together, and the moist powder gradually thrown in, and kept 
at a red heat for an hour in a covered crucible. The ultra- 
marine is then separated by washing. 
In what state the sulphur and the alkali exist in this com¬ 
pound has not been ascertained. 
Guimet in France first succeeded in producing this pigment, 
by a process probably more economical, but which has not 
been made public; and in that country it is already manufac¬ 
tured in considerable quantities. 
Electro-positive Metals , reduction of. —Since the brilliant 
discovery of the metallic bases of the alkalies and earths by 
Davy, processes have been devised, by means of which those 
of the alkalies can be obtained in large quantity. Most of the 
earths, however, continued refractory, and chemists were un¬ 
acquainted, till lately, with any process by which they could be 
decomposed. In 1828 this difficulty was overcome by Wohler, 
who, by preparing anhydrous chlorides and heating them with 
potassium, succeeded in reducing alumina, glucina, and yttria. 
By the same process in the following year Berzelius reduced 
thorina, and Bussy magnesia. 
The metals obtained from these oxides are much more per¬ 
manent than the bases of the alkalies ; they may be boiled in 
water without oxidation, burn when heated in the open air, 
and are dissolved by acids with evolution of hydrogen gas. 
Potash .—Fuchs * has proposed to prepare potash for com¬ 
mercial purposes from felspar and mica. The minerals are re¬ 
duced to powder, calcined in a furnace with quick lime, and 
afterwards exposed to air and moisture for some time; the 
alkali is then washed out: by this process felspar should give 
about one fifth of its weight of potash. 
Barytes and Strontian, separation of. —Liebig f proposes 
iodate of soda as an excellent means of separating these two 
* Roy. Inst. Journ. i. p. 184. f Journ. de Pharm. April 1882, p. 214. 
