34 
Figs. 12 and 13.— Potash-saltpetre, Nitrate of 
Potash, Saltpetre. 
The primary form is a right-rhombic prism of 119°, 
with the cleavage in greatest perfection, parallel to the 
planes of the sides and to the planes of truncation of the acute 
lateral edges; transversely, however, it presents a conchoidal 
uneven plane with a greasy lustre ; externally the lustre is 
vitreous. More frequently truncations of the acute lateral 
edges, and of all the basal edges occur, so that a combination 
of the prism with the hexagonal pyramid appears, similar 
to that of the quartzoid (Fig. 13), or a double truncation of 
the acute angles (Fig. 12). The natural crystals are mostly 
very small and irregular, like the Indian saltpetre which 
comes to Europe from the course of the Lower Ganges, 
in impure crystalline grains; but by dissolving in water, 
and gradually cooling it, very fine crystals can be obtained. 
Pure saltpetre is colourless, transparent, friable, of 2*0 hard¬ 
ness, and 1*9—2'0 sp. gr. It is simple nitrate of potash; 
K N, composed of 46*56 potash and 53*44 nitric acid. As it 
is found in nature, it generally contains a little carbonate and 
sulphate of lime, bitumen, etc. A solution in water has a 
cooling salt taste, slightly acid. Sprinkled on live charcoal 
it decrepitates and melts. In the platinum forceps, it colours 
the flame of the blow-pipe violet, by which it may be easily 
distinguished from soda-saltpetre. It occurs in Hungary 
and Siberia in considerable quantities. Saltpetre is now 
generally artificially prepared in what are called saltpetre- 
plantations, by mixing up rich mouldy earth with burned 
lime, and the ashes of plants moistened with various animal 
substances, and exposed to the influence of the atmosphere. 
Saltpetre is used in medicine, for the preservation of meat, 
for making gunpowder, nitrates, and other preparations. 
The sylvinsalz , which has of late years frequently been 
found in considerable quantity as an efflorescence of lava, 
particularly at Vesuvius in 1822, is a chloride of potassium 
more or less mixed with chloride of sodium, which occurs 
in bluish crystalline masses, and when moistened with 
sulphuric acid, it gives off hydrochloric acid, and otherwise 
gives the reactions of soda and potash. The amount of 
chloride of sodium varies from 46*2 to 62*0 per cent, and 
it may be used both for the preparation of chlorine and 
hyrochloric acid, and of the compounds of potash and 
soda. 
X. SALTS 
The compounds of soda which we are about to enu¬ 
merate are more widely distributed in nature than the potash 
salts, and moreover, they sometimes occur of remarkable 
purity. All of them are readily soluble in water, have a 
saline taste, and colour the flame of the blow-pipe a deep 
yellow. They are compounds of inorganic acids, with the 
oxide of sodium, or of chlorine with sodium ; the latter 
class are the most important. 
Figs. 14 and 15.— Carbonate of Soda, Soda. 
The primary form is an oblique rhombic prism of 
103° 84' and 76° 12', which generally occurs combined 
with truncation of the basal edges (Fig. 15); sometimes, 
however, it is found with truncation of two basal and lateral 
edges. More frequently crystalline granules and salt-like 
crusts occur, more or less mixed up with gypsum, chloride 
of sodium, and earthy substances of a white, grey, or yellow 
colour. Easily soluble in water; of 1*0—1*5 hardness, and 
1*4—1*5 specific gravity. The constituents are simple 
carbonate of soda, with ten equivalents of water = Na C 
+ 10 H. The crystals crumble down in the atmosphere, 
and give off their water of crystallization; they melt very 
readily before the blow-pipe, and colour the flame yellow. 
When held in the outer flame in a loop of platinum wire, 
with a small amount of oxide of manganese, it gives a fine 
greenish-blue coloured pearl of manganate of soda, which 
becomes dim on cooling. It is found in large quantities 
in the natron-lakes of Lower Egypt, westward from the 
Nile, whence in earlier times it was brought by traders; 
at Debrecsin, and in other parts of Hungary, the soil is so 
strongly impregnated with soda that the land is sometimes 
covered with white acicular crystals of this salt. In 
former times much soda, was obtained from the ashes of 
sea-plants ; now-a-days it is mostly extracted artificially 
from rock or sea-salt. It is used in the manufacture of 
OF SODA. 
soap and glass, for bleaching, and for many chemical pre¬ 
parations ; also in a pure state as a blow-pipe test, and for 
distinguishing the different silicates. 
Trona or urao is another compound of sesqui-carbonate 
of soda and water = Na 3 C 3 + 2 H, which occurs in 
oblique rhombic prisms of 103° 15 / , generally with trunca¬ 
tion of the obtuse angles (Fig. 14), of 2*0—3*0 hardness, 
and 2*11 specific gravity; vitreous lustre, colourless, passing 
into grey and yellow, translucent, not decomposed by the 
atmosphere, readily soluble in water, and of a tolerably 
alkaline taste. It is found in Egypt and other parts of 
Northern Africa, as w T ell as at Lagunilla in Columbia, and 
may be used as soda. It also behaves like soda before the 
blow-pipe. Soluble in acids with effervescence. 
Figs. 16—20, 21. — Rock-Salt, Chloride of Sodium, 
Common Salt. 
The primary form is the cube, with cleavage in the 
direction of the planes. Combinations of the cube and 
octahedron, however, occur also (Fig. 20), and truncations 
of the edges; crystalline-granular masses, of the appearance 
of coarsely-grained quartz, are more common. Fibrous, 
foliated, and compact forms occur in an isolated condition. 
In general colourless, the crystals sometimes transparent in 
the highest degree, sometimes blue or red. Especially 
fine sapphire-blue varieties are obtained in the Salzburg 
district; finely granular and fibrous rock-salt, reddened 
by oxide of iron, is found especially at Hallein and Bereh- 
tesgaden; a brownish-red and long fibrous variety occurs 
at Wilhelmsgliick on the Kocher (Fig. 16), where the 
granular salt reaches the thickness of from 20 to 30 feet, 
and the lower layers are crystallized. Cubes of a foot in 
diameter, and perfectly transparent, have been found 
here. Fracture even, of vitreous to fatty lustre, friable, 
the hardness = 2*5, the specific gravity = 2*2—2*3. 
