Iciated with carbon. In all fuels containing carbon, hydrogen, and oxygen, the proportion of hydrogen may be equal to, or greater than, but seldom less than that required to form water with the oxygen. The amount of hydrogen which is chemically united with oxygen is not available as a source of heat, so that the excess of hydrogen over this amount is called "disposable" hydrogen, and the amount in combination the "non-disposable" hydrogen.

Calorific power. The amount of heat a body is capable of yielding when completely burned is termed its calorific power. The calorific power of different bodies is given in the following table :

Wood-charcoal,

Gas-carbon,

Artificial graphite,

8080

8047.3

7762.3

Native graphite,

7796.6

Diamond,

7770.1

The number 8080 for wood-charcoal signifies that 1 lb. of that body, when completely oxidised to carbonic acid, will produce sufficient heat to raise 8080 lbs. of water 1° C.; and so on for the rest. The calorific power of a fuel containing carbon, hydrogen, and oxygen would be the sum of the calorific powers of the carbon and that of the disposable hydrogen.

The bodies used as fuel are-wood, peat, coal, petroleum, and natural gas. From some of these are obtained prepared fuels, such as charcoal, coke, etc.

Charcoal is prepared by heating wood to a temperature of about 400° C. in a covered pile, or in a closed vessel, so as to admit only a limited supply of air. This is the purest form of solid fuel.

Coke is made in a similar way to charcoal in piles, in kilns, and in ovens. The bee

hive-oven Fig. 1 is a somewhat circular chamber of brickwork, with an arched roof, having a chimney opening at the top for the escape of the products of combustion and vapours. The cavity

Fig. 1.

is about 9 feet to 10 feet in diameter, and 4 feet to 5 feet high. The charge is introduced through a doorway in front, about 2 feet square, through which the charge is also withdrawn. These ovens are generally built in two rows back to back, with a charge of three tons in each, which reaches up to the springing of the dome of the roof. When the charging is completed, the doorway is loosely filled up with bricks, through the openings of which the air can pass. In some ovens an iron door is used. Supposing the oven to be hot from a previous charge, in three hours the lower holes are closed, and in twenty-four hours the upper ones are closed. The oven is now allowed to remain twelve hours

with the chimney open. When the flame ceases, the damper is closed, and the oven allowed forty-eight hours to cool. The charge is then withdrawn by means of a large shovel suspended by a crane, and the hot coke quenched with water.

Pyrometers.-The heat of a furnace is measured by an instrument called a "pyrometer." A good pyrometer must be capable of giving a constant indication for the same temperature, and must not

change with use. Various methods are employed for this purpose.

The temperature of the hot-blast, used for the blastfurnace, is generally determined by its power of fusing certain metals whose melting points are known. Tunner uses different alloys of silver and platinum for measuring the temperature of a furnace. Pouillet exposes a ball of copper or of platinum of given weight to the heat of the furnace, and then rapidly transfers it through a clay tube to a vessel containing a known weight of water, at a known temperature. From the increase in temperature of the water the temperature of the furnace is calculated. The mode of calculation is as follows:

T is the temperature, t't the rise in tem perature of water, W the weight of water, w the weight of ball, and s its specific heat. bb To this result must be added the observed temperature of the water. Daniell estimated high temperatures by means of a rod of platinum placed in a plumbago tube. The inner end of the platinum was fixed, while the outer end pressed against a lever serving as an index. He assumed that the expansion was proportional to the temperature. Siemens' electric resistance pyrometer is far superior to the foregoing arrangements and is represented in part in Fig. 2. It consists of a platinum spiral (a) of known Fig. 2. resistance, wound on a cylinder of fire-clay, and enclosed in a casing of platinum or copper according to the temperature to be measured. The two ends of the coil are connected by thick platinum wires with two thick copper wires, at the part which is less strongly heated. These wires are insulated by

α

pipeclay tubes (bb) and communicate with the measuring instrument by which the resistance is measured. The electric resistance of platinum is increased fourfold by a rise in temperature from 0° to 1650° C. The portion (cd) which is exposed to the highest temperature of the furnace is encased in wrought iron or platinum, and the outer portion (c e) is enclosed in an iron tube. The outer tube is shown in Fig 2A, and the resistance arrangement in Fig. 2B.

QUESTIONS.

1. What is an ore? In what condition are iron ores for example usually found?

2. What do you understand by the term "dressing" as applied to ores? Mention cases in which this is unnecessary. 3. What object is gained by submitting an ore to calcination or roasting?

4. What is a slag; how is it formed; and for what purpose is it produced?

5. What is a flux? By what principles would you be guided in the choice of a flux?

6. What conditions are necessary to produce a good weld? Why will not pig-iron weld?

7. What do you understand by the term "cementation" as applied to iron and steel?

8. Explain the terms "fining" and "refining" and mention operations to which your answer is applicable.

9. What is meant by the terms "red-short" and "cold-short" when applied to malleable iron, and to what causes are those properties commonly attributed?

10. What are the most characteristic properties of a metal? What do you understand by the term "metal"?

11. Explain the terms "malleability,” “

tenacity" as applied to metals.

'ductility," and

12. What do you understand by a "tough" metal?

13. Define the terms "elasticity" and "limit of elasticity." 14. Name the different kinds of fracture in metals and give an example of each kind.

15. What do you understand by a refractory substance? Give a few examples.

16. What is a crucible? Of what materials are crucibles made?

17. What is fire-clay? How does it differ from sand? 18. What is the nature of the substance called "ganister" and for what purposes is it used?

19. What is Dinas clay? How is it made into bricks? 20. What is dolomite, and for what purposes is it employed in steel making?

21. What kind of a substance is Bauxite?

Under what

circumstances would you use it as a furnace-lining?

22. What is charcoal, coke, and anthracite?

23. What is the use of a pyrometer? Describe any useful pyrometer with which you are acquainted.

CHAPTER III.

CHEMICAL PRINCIPLES AND CHANGES.

THE present chapter is intended for the non-chemical student, so as to impart a better conception of the chemical changes involved in the various operations connected with iron and steel manufacture.

Chemists have found that all bodies, whether in the form of a solid, a liquid, or a gas, are either simple substances or can be resolved into simple substances, termed "elements." These elements are represented by symbols, which are usually the initial letter or letters of their names. Different elements combine together in definite proportions forming an endless variety of substances, termed "compounds."

Elements are classified into "metals" and "non-metals," the former being distinguished by well marked properties, which are absent in the latter. The ultimate particles or "atoms" which compose any element differ in weight