shown in fig. 63. A represents a ball of platinum or other metal or alloy, according to the supposed temperature. B is a vessel of water. The portion a, a, is of brass, with two holes in the upper part; one, b, b,

for the mixer, and the other, c, c, for the mercurial thermometer. There is also another hole at the lower part, d, by which the water is emptied. e, e, is a wooden case well screwed together. The mixer C consists of a conical ring, f, and wires of brass, which connected with the lower part of the ring, form the small cage, g. The upper portion is prolonged into a funnel, and has attached to it a small handle, h, used to take hold of and turn the mixer. The thermometer

FIG. 63.

k, surrounded with the case 1, is graduated to show onetenth of a degree Centigrade.

Fig. 64 shows how the instrument is arranged. Place the

ball A on the end of the rod C, which is then introduced and slid along the two points a, b, to the end of the muffle E, through the opening D. Then push the wedge-shaped

stopper f into this opening, until the rod, which is balanced on the point b, touches the point e. Then close the mouth D with clay.

As soon as the ball has acquired the temperature of the furnace (in three or four minutes), draw out the rod. The ball touching the point e becomes detached and falls, rolling down the canal g, k, closed below by the valve l, when it falls into the vessel previously filled with a determined weight of water, B, through the funnel f. After having closed the funnel with a cork, turn the mixer very slowly two or three times, slightly shaking the instrument at the same time.

By taking the temperature of the water before (t) and after (t') the operation, the difference (tt) is easily found. Reference is then made to the following table (see p. 137).

This table is calculated for the weights of 300 grammes of water, 7 grammes of steel, and 8 grammes of platinum. For each degree t—t, a temperature x is found to correspond, to which is added the final temperature ť.

r the corresponding temperature = 660° x the corresponding tempera

ť.

t'

= 17

ture

= 1550°

= 20

= 1570

One or two other methods of measuring high temperatures applicable to special cases may here be mentioned.

Becquerel has proposed a very excellent plan for measuring high temperatures, by means of the thermo-electric current generated by heating the junction of two platinum wires of different diameters. In a similar manner, the thermo-electric current produced by heating two wires of platinum and palladium, melted together at one end, has been used as a pyrometer.

A good plan for comparing the temperatures of two furnaces is to prepare alloys of platinum and gold, containing definite quantities, say, 5, 10, 15, 20 % &c. of gold.

Observation.x + t' is the temperature of the furnace.

These fuse at intermediate temperatures between gold and platinum. By placing small angular chips of these alloys separately in muffles, and noticing which are melted, which softened only, and which resist the action of the heat, an idea of the power of the furnace is obtained. In this way the amount of heat required to perform any operation may be registered for future reference, by simply recording that it was sufficient just to melt, say a 20 gold 80 platinum alloy.

138

CHAPTER V.

FUEL ITS ASSAY AND ANALYSIS.

BEFORE treating of the assay of metals and metalliferous ores, it is advisable to devote some space to the important subject of fuel. The substances employed as fuel, although all of vegetable origin, are derived either from the vegetable kingdom (wood), or from the mineral kingdom (peat, brown coal, coal, anthracite). These natural fuels can be converted into artificial fuels by heating them more or less out of contact with the air (charcoal, turf-charcoal, coke).

The essential elements of combustible matters are carbon, oxygen, and hydrogen; nitrogen being present sometimes, but only in small proportions. These constitute the organic part; various salts and silica constitute the inorganic part, or ash. The valuable constituents of fuel, on which its calorific and reducing powers depend, are the carbon and hydrogen, and it is upon the combustion or union of these elements with oxygen to form carbonic acid and water, that the effect of the fuel depends.

The more oxygen a fuel contains the less carbon and combustible gases it will yield, and the more hydrogen, the more combustible gases.

The proportion of hydrogen to oxygen in wood

is 1:7

turf
fossil-wood

1:6

1:4

The more oxygen, the less carbon the fuel contains, thus:

Anthracite contains about 90% carbon

The more carbon a fuel contains, the greater heat it produces, and the more difficult it is to ignite.

The greater the amount of hydrogen in a fuel, the more inflammable it will be, and the larger flame it gives, the hydrogen being evolved below a red heat. But the more carbon present, the less flame. These differences are shown in a blazing fire and a glowing fire. In a flame the hottest part is at the periphery, whilst in a glowing fire the greatest heat is in the immediate contact of the burning surface.

The assay of fuel comprises the following examinations : 1. The examination of the external appearance of the fuel, its porosity or compactness, its fracture, the size and shape of the pieces composing it.

2. Determination of the adhering water.

3. The specific gravity.

4. Determination of the absolute heating power. 5. Determination of the specific heating power.

6. Determination of the pyrometric heating power.

7. Determination of the volatile products of carbonisation.

8. Examination of the coke or charcoal left behind on carbonisation, both with regard to quality and quantity. 9. Determination of the amount of ash, and its composition.

10. Determination of the amount of sulphur.

11. Examination of any other peculiarity which may be noticed during the burning or carbonisation of the fuel.

1. EXTERNAL APPEARANCE OF THE FUEL, ITS POROSITY, COMPACTNESS, FRACTURE, SIZE, AND SHAPE OF PIECES. From the outward appearance of a fuel, its cleavage, and an examination of the embedded earthy matter, iron pyrites, gypsum, &c., its applicability to any special purpose may be judged. Its degree of inflammability, together with the pressure of blast which it will bear in the furnace, partly depends on the more or less compactness of the fuel. The amount of loss which it will suffer in transport depends upon its friability. Playfair and De la Beche* determined Dingl. ex. 212, 263; cxiv. 346. Liebig's 'Jahresber.,' 1847-1848, p. 1117 1849, p. 708.