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iron bars; this passes over suitable drums at the front and back of the boiler, by the slow rotation of which the grate travels very slowly from front to back. The See also:

COAL

coal, which is broken small, is fed from a hopper over the whole width of the grate, the thickness of the See also:

FIRE (in O. Eng. f j'r; the word is common to West German languages, cf. Dutch vuur, Ger. Feuer; the pre-Teutonic form is seen in Sanskrit pu, pavaka, and Gr. irup; the ultimate origin is usually taken to be a root meaning to purify, cf. Lat. purus)

fire being regulated by a See also:

DOOR (corresponding to the Gr. Bbpa,. Lat. fores or valvae; the English word, with other forms common in allied languages, comes from the same Indo-European stem as the Gr. Obpa and Lat. fares)

door which can be raised or lowered as desired. Thus the volatile portions of the coal are distilled at the front of the fire, and pass over the incandescent See also:

FUEL (O. Fr. feuaile, popular Lat. focalia, from focus, hearth, fire)

fuel at the back end. The See also:

SPEED, JOHN (1552–1629)

speed of travel is so regulated that by the time the remaining parts of the fuel reach the back end the combustion is nearly See also:

COMPLETE

complete. It will be seen that the fire becomes thinner towards the back, and too much air is prevented from entering the thin portion by means of vanes actuated from the front of the boiler. See also:

DRAUGHT (from the common Teutonic word " to draw "; cf. Ger. 7'racht, load; the pronunciation led to the variant form " draft," now confined to certain specific meanings)

Draught.—In most boilers the draught necessary for combustion is " natural," i.e. produced by a chimney. For marinecombustion of about 15 to 20 lb. of coal per sq. ft. of grate See also:

AREA

area per See also:

HOUR

hour can be obtained.

With forced draught much greater rates can be maintained, ranging from 20 lb to 35 lb in the larger vessels with a moderate air pressure, to as much as 70 and even 8o lb per sq. ft. in the See also:

EXPRESS (through the French from the past participle of the Lat. exprimere, to press out, by transference used of representing objects in painting or sculpture, or of thoughts, &c. in words)

express types of boiler used in See also:

TORPEDO

torpedo boats and similar See also:

CRAFT (a word common to Teutonic languages for strength, or power; cf. Ger. Kraft)

craft. Performance of Boilers.—The makers of several types of boilers have published particulars regarding the efficiency of the boilers they construct, but naturally these results have been obtained under the most favourable circumstances which may not always represent the conditions of See also:

ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

ordinary working. The following table of actual results of marine boiler trials, made at the instance of the See also:

BRITISH

British See also:

ADMIRALTY, HIGH COURT OF

admiralty, is particularly useful becuase the trials were made with See also:

GREAT

great care under working conditions, the whole of the coal being weighed and the feed-See also:

WATER

water measured throughout the trials by skilled observers. The various trials can be compared amongst themselves as See also:

South Welsh coal of excellent quality was used in all cases. In experimental tests such as those above referred to, many conditions have to be taken into See also:

account, the See also:

PRINCIPAL

principal being the duration of the trial. It is essential that the See also:

CONDITION (Lat. condicio, from condicere, to agree upon, arrange; not connected with conditio, from condere, conditum, to put together)

condition of the boiler at the conclusion of the test should be precisely the same as at the commencement, both as regards the quantity of unconsumed coals on the fire-grate and the quahtity of water and the See also:

steam-pressure in the boiler. The longer the See also:

period over which the observations are taken the less is the See also:

INFLUENCE (Late Lat. influentia, from influere, to flow in)

influence of errors Duration coal See also:

ion o in the estimation of these particulars. Further, in See also:

order properly to represent working conditions, the See also:

RATE

rate of combustion of the fuel throughout the trial must be the same as that intended to be used in ordinary working, and the duration of the test must be sufficient to include proportionately as much cleaning of fires as would occur under the normal working conditions. The tests should always be made with the See also:

KIND (O. E. ge-cynde, from the same root as is seen in " kin," supra)

kind of coal intended to be generally used, and the records should include a test of the calorific value of a See also:

SAMPLE (through the O. Fr. essemple, from Lat. exemplum; a doublet of " example ")

sample of the fuel carefully selected so as fairly Air f thechimney Water Evaporated evapor- Efficiency be conveniently treated together, because similar materials and methods are employed in each, notwithstanding that many points of divergence in practice generally relegate them to See also:

SEPARATE

separate departments. The materials used are chiefly iron and See also:

STEEL, FLORA ANNIE (1847– )

steel. The methods mostly adopted are those involved in the working of plates and rolled sections, which vastly predominate over the bars and rods used chiefly in the smithy. But there are numerous See also:

DIFFERENCES, CALCULUS OF (Theory of Finite Differences)

differences in methods of construction.

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