Chap. II.
combines with cyanogen, and forms several important compounds, uniting invarious proportions with other bodies. Prussian Blue is a ferrosesquicyanuret of iron, andhas a peculiarly rich colour, of an intense blue with a copper tint on its surface; it is in-soluble in water, in alcohol, and in dilute acids; the anhydrous variety consists of
Iron
-
- 7
-
196
.
45*5
Carbon
-
- 18
-
108
.
25*2
Nitrogen
-
- 9
-
126
-
29 3
1
430
100*
Alloys of Iron . — Iron and potassium form a white soft alloy, which effervesces in water ;that of iron and manganese is white, hard, and brittle, and is said to give a peculiarcharacter to steel.
Salts of Iron are generally soluble in water, and the solution by exposure to the airbecomes of a reddish brown; with ferrocyanuret of potassium, a pale or deep blue preci-pitate ; and with the hydrosulphuret of ammonia a black precipitate.
The Persalts of Iron , as the permuriate and the persulphate, furnish a red precipitate,when the solutions are concentrated, upon the addition of sulphocyanic acid and the solublesulphocyanates: none of the metals precipitate iron in a metallic state, zinc and cadmiumexcepted.
The weight of a cubic foot of cast-iron is 450*5 pounds avoirdupois, and of wrought468*8 pounds, the weight of a cubic inch of the former being *260 pounds, and of thelatter *281. It has been found that 93,000 pounds upon a square inch of wrought iron issufficient to crush it, and that it will bear 15,000 pounds without any apparent change inits particles.
The quantity of pig-iron, manufactured in South Staffordshire in the year 1839, was es-timated by Mr. Mushet as amounting to 346,213^ tons, and in Shropshire 80,940 tons,being together nearly two-thirds of the whole quantity made in the United Kingdom . Thematerials for its manufacture are coals, ironstone, and limestone ; the first, when intendedfor the cold-blast furnace, previously to its application, is made into coke; the ironstoneundergoes roasting and calcining, and the limestone is broken into small lumps: afterthese operations they are mixed, or thrown into the blast furnace, in certain definite pro-portions.
The Coke is made by burning the coal in large heaps 4 or 5 feet high in the open air, thepieces being placed side by side, care being taken that they lie sufficiently loose near theground to admit of a free current beneath them ; these heaps contain as much as 20 or 21tons. In some parts of Staffordshire , a brick funnel 2 feet in diameter, with occasional sideapertures, is carried up to the height of 4 or 5 feet, and around which the coal or slack isheaped and continually watered. After the fire has been burning for 4 days, the coke issufficiently made, and water is thrown over it to extinguish the fire and carry off thesulphur : 2 tons of coal so treated produce 1 ton of coke. In Shropshire the heaps do notgenerally contain more than 13 or 14 tons, and are suffered to burn 10 or 12 days, when alight blue lambent flame makes its appearance; the sides are covered with wet coke dust,and afterwards the top.
Calcining the Ironstone. — The ironstone in Staffordshire and Colebrook Dale is argil-laceous. In some pits it is in bands 1, 2, or 3 inches thick, with measures of induratedclay, perhaps several feet thick, between; in others it is in boulders distributed through abed of indurated clay, or of clay and sand. The boulders vary in size from that of a smallapple to masses weighing many hundred weight. The usual form is that of a flattenedspheroid; after the ironstone is taken out of the pit, it is laid in heaps exposed to the sunand air, for the purpose of evaporating as much of the water as possible. Before calcinationthe larger boulders are broken into pieces about the size of a man’s fist, that the fire mayact equally on all.
The ironstone is burnt on the ground like the coke, a layer of coals of several inches inheight is laid down with the points touching the ground, so as to admit the air below ; uponthis is a layer of ironstone, then another of coals alternately, until the heap, becomingnarrower with every layer, terminates in a point, after which small coal is spread over thewhole, and fire is introduced at the bottom : this gradually spreads along the ground,penetrating upwards through the whole heap, and lambent flames are seen issuing betweenthe pieces of the ironstone; in ten or twelve days the operation may be completed, and theironstone being cooled is ready for the furnace.
The effects of calcining the ironstone are, to drive off first the remaining water, whichwould materially diminish the quantity of iron produced in the furnace, and injure itsquality ; secondly, the sulphur, which would produce the same effect; thirdly, the carbonicacid, which adds considerably to its weight, as it does to that of chalk or limestone. If thefire be continued too long, the ironstone, and all metals similarly treated, imbibe oxygen,and its quality is injured.