680
THEORY AND PRACTICE OF ENGINEERING.
Book II.
indicates by the loss of weight the quantity of carbonic acid gas which has escaped. The acidcontents are then evaporated to dryness and digested in water, when the silica is alonefound insoluble. The solution somewhat acidulated, and oxalate of ammonia added, thelime is precipitated in the form of an oxalate. Alumina and the oxide of iron are alsoprecipitated by ammonia. The manganese may be thrown down by hydrosulphuret ofpotash, and the magnesia by carbonate of soda. The red oxide of iron contains 69*34 ofmetal, and 80*66 of oxygen.
To ascertain the quantity of iron contained in 100 parts without reference to the othermaterials comprised in the ore, a more simple method may be adopted. Hot nitric ormuriatic acid is poured upon the ore, the solution filtered, and supersaturated with am-monia, when the iron oxide and alumina arc alone thrown down. This red precipitate,digested with potash lye, gives the oxide of iron nearly pure.
Native iron is occasionally found, and is considered as of meteoric origin, in consequenceof its containing a small quantity of nickel, the usual alloy of meteoric stones.
Iron and Oxygen. —Heat, air, and moisture, have the effect of oxidising iron, and con-verting it, according to circumstances, into either a protoxide or peroxide, and the twolatter are salifiable bases.
Protoxide of Iron is seldom found pure ; it is of a dark colour, and usually contains asmall quantity of the peroxide; it is obtained by burning iron in oxygen, which whenheated red-hot drops in the state of oxide. It is insoluble in water, tasteless, and of ablack colour. Its equivalent is 28, and it contains —
Iron -
_
_
1
_
28
- 77*6
Oxygen
1
1
8
36
- 22'4
100*0
Peroxide of Iron is in the state of a red powder, when sulphate of iron is decomposed at avery high temperature ; the colour varies according to the method adopted to obtain it;sometimes it is of a yellow brown, which acquires a darker tint by heating. Iron rustconsists of the peroxide in union with water, and traces of carbonic acid and ammonia arefound in it, the acid being derived from the air, the ammonia from the nitrogen of the aircombining with the hydrogen of the water.
Iron -
-
-
1
-
28
-
70
Oxygen
-
-
n
-
12
-
30
i
40
100
Iron and Carbon .—Cast-iron and steel are bodies which contain more or less carbon, and,as already observed, it is from the carbonates of iron in a native state that the chief metal isobtained. The clay iron ore of our coal districts is an impure protocarbonate of iron.
The Protocarbonate of Iron consists of
Protoxide of iron
- 1
.
36
62
Carbonic acid
- 1
-
22
38
1
58
100
Iron unites with chlorine in two proportions, viz. the protochloride and a perehloride.
Native Sulphurets of Iron . — Among these are the magnetic pyrites , which is a proto-sulphuret of iron, and the common pyrites, which is a bisulphuret, crystallised in avariety of forms, having their origin in a cube; their colour is a brass yellow; they areused to produce green vitriol, or sulphate of iron, and as a source of sulphur in the pro-duction of sulphuric acid.
The Bisulphuret of Iron contains
Iron
.
_
- 1
-
28
-
46*6
Sulphur
-
-
. o
-
32
-
53-1
1
60
100*0
Sulphates of Iron arc used in the preparation of ink, Prussian blue , peroxide of iron, andcarbonate of iron.
Protophosphate of Iron is found native in the state of a blue earthy powder, and sometimesin prismatic crystals; it is said to contain
Phosphoric acid - - - - - 31
Protoxide of iron - - - - - 41
Water « - - - - - 28
1(X)