M. Béchamp on the Preparation of Permanganate of Potash. 383 
decanted and evaporated to dryness in a platinum crucible; a 
small quantity of carbonate of ammonia is added occasionally 
during the evaporation, and when the mass becomes pasty, it is 
stirred with a platinum spatula. The dried salt may be kept in 
vessels of platinum, silver, or gutta percha. 
In order to decompose a silicate, it is mixed in a state of fine 
powder with six times its weight of fluoride of ammonium, a 
small quantity of water added, and the mixture heated at first 
gently, and gradually.to redness as long as vapours are given off. 
Usually one operation is sufficient; the residue is treated with 
sulphuric acid, and the excess of this acid driven off. Where 
the sulphates formed do not completely dissolve in water con- 
taining a little hydrochloric acid but leave a residue, the inso- 
luble part is again treated with fluoride of ammonium. 
The temperature must not be raised too high in the operation ; 
for if the silicate contained alumina a fluoride of aluminum 
might be formed, difficult to be decomposed by sulphuric acid. 
Hyposulphite of soda, according to Léwe*, dissolves sulphate 
of lead, which may in this way be separated from sulphate of 
baryta. A concentrated solution of hyposulphite is poured on 
the mixture of the two salts, and the whole digested between 
15° and 20°. At a higher temperature a sulphide of lead inso- 
luble in hyposulphite of soda might be formed. The residual 
sulphate of baryta carefully washed is weighed, and as a control 
the lead in the hyposulphite may also be determined. 
For the preparation of permanganate of potash, Béchamp + 
recommends the following method. In an iron basin ten parts 
of powdered binoxide of manganese are mixed with twelve parts 
of fused caustic potash; a little water is added to the mixture, 
which is rapidly dried, and introduced while still hot into a tubu- 
lated stoneware retort, and a current of pure dry oxygen passed 
into it. To the neck of the retort a tube is fitted just dipping 
ander mereury. The absorption of oxygen is very rapid; it is 
complete when it bubbles through the mercury. The cooled 
mass is then exhausted with hot water, anda current of carbonic 
acid passed through the solution, by which the manganate is 
transformed into permanganate. When the solution has the 
characteristic colour of the permanganate the current of gas is 
stopped, the oxides of manganese are allowed to settle, the clear 
solution rapidly evaporated and allowed to crystallize ; the mother- 
liquors yield a further crop of crystals. In general a pound of 
binoxide gives five to six ounces of permanganate at the first 
crystallization. 
* Journal fiir Praktische Chemie, vol. \xxvii. p. 75. 
+ Annales de Chimie et de Physique, November 1859. 
