Volume 2, Slice 2 Part 4 (2/2)
A grade of steel must be selected of suitable quality for the purpose for which it has to be used. There are a number of such grades, ranging from about 1 to % content of carbon, and each having its special utility. Overheating must be avoided, as that burns the steel and injures or ruins it. A safe rule is never to heat any grade of steel to a temperature higher than that at which experience proves it will take the temper required. Heating must be regular and thorough throughout, and must therefore be slowly done when dealing with thick ma.s.ses.
Contact with sulphurous fuel must be avoided. Baths of molten alloys of lead and tin are used when very exact temperatures are required, and when articles have thick and thin parts adjacent. But the gas furnaces have the same advantages in a more handy form. Quenching is done in water, oil, or in various hardening mixtures, and sometimes in solids.
Rain water is the princ.i.p.al hardening agent, but various saline compounds are often added to intensify its action. Water that has been long in use is preferred to fresh. Water is generally used cold, but in many cases it is warmed to about 80 F., as for milling cutters and taps, warmed water being less liable to crack the cutters than cold. Oil is preferred to water for small springs, for guns and for many cutters.
Mercury hardens most intensely, because it does not evaporate, and so does lead or wax for the same reason; water evaporates, and in the spheroidal state, as steam, leaves contact with the steel. This is the reason why long and large objects are moved vertically about in the water during quenching, to bring them into contact with fresh cold water.
There is a good deal of mystery affected by many of the hardeners, who are very particular about the composition of their baths, various oils and salts being used in an infinity of combinations. Many of these are the result of long and successful experience, some are of the nature of ”fads.” A change of bath may involve injury to the steel. The most difficult articles to harden are springs, milling cutters, taps, reamers. It would be easy to give scores of hardening compositions.
Hardening is performed the more efficiently the more rapidly the quenching is done. In the case of thick objects, however, especially milling cutters, there is risk of cracking, due to the difference of temperature on the outside and in the central body of metal. Rapid hardening is impracticable in such objects. This is the cause of the distortion of long taps and reamers, and of their cracking, and explains why their teeth are often protected with soft soap and other substances.
The presence of the body of heat in a tool is taken advantage of in the work of tempering. The tool, say a chisel, is dipped, a length of 2 in.
or more being thus hardened and blackened. It is then removed, and a small area rubbed rapidly with a bit of grindstone, observations being made of the changing tints which gradually appear as the heat is communicated from the hot shank to the cooled end. The heat becomes equalized, and at the same time the approximate temperature for quenching for temper is estimated by the appearance of a certain tint; at that instant the article is plunged and allowed to remain until quite cold. For every different cla.s.s of tool a different tint is required.
”Blazing off” is a particular method of hardening applied to small springs. The springs are heated and plunged in oils, fats, or tallow, which is burned off previous to cooling in air, or in the ashes of the forge, or in oil, or water usually. They are hardened, reheated and tempered, and the tempering by blazing off is repeated for heavy springs. The practice varies almost infinitely with dimensions, quality of steel, and purpose to which the springs have to be applied.
The range of temper for most cutting tools lies between a pale straw or yellow, and a light purple or plum colour. The corresponding range of temperatures is about 430 F. to 530 F., respectively. ”Spring temper”
is higher, from dark purple to blue, or 550 F. to 630 F. In many fine tools the range of temperature possible between good and poor results lies within from 5 to 10 F.
There is another kind of hardening which is of a superficial character only--”case hardening.” It is employed in cases where toughness has to be combined with durability of surface. It is a cementation process, practised on wrought iron and mild steel, and applied to the link motions of engines, to many pins and studs, eyes of levers, &c. The articles are hermetically luted in an iron box, packed with nitrogenous and saline substances such as potash, bone dust, leather cuttings, and salt. The box is placed in a furnace, and allowed to remain for periods of from twelve to thirty-six hours, during which period the surface of the metal, to a depth of 1/32 to 1/16 in., is penetrated by the cementing materials, and converted into steel. The work is then thrown into water and quenched.
[Ill.u.s.tration: FIG. 1.--Automatic Oil m.u.f.fle Furnace.]
A m.u.f.fle furnace, employed for annealing, hardening and tempering is shown in fig. 1; the heat being obtained by means of petroleum, which is contained in the tank A, and is kept under pressure by pumping at intervals with the wooden handle, so that when the valve B is opened the oil is vaporized by pa.s.sing through a heating coil at the furnace entrance, and when ignited burns fiercely as a gas flame. This pa.s.ses into the furnace through the two holes, C, C, and plays under and up around the m.u.f.fle D, standing on a fireclay slab. The doorway is closed by two fireclay blocks at E. A temperature of over 2000 F. can be obtained in furnaces of this cla.s.s, and the heat is of course under perfect control.
[Ill.u.s.tration: FIG. 2.--Reverbatory Furnace.]
A reverberatory type of gas furnace, shown in fig. 2, differs from the oil furnace in having the flames brought down through the roof, by pipes A, A, A, playing on work laid on the fireclay slab B, thence pa.s.sing under this and out through the elbow-pipe C. The hinged doors, D, give a full opening to the interior of the furnace. It will be noticed in both these furnaces (by Messrs Fletcher, Russell & Co., Ltd.) that the iron casing is a mere sh.e.l.l, enclosing very thick firebrick linings, to retain the heat effectively. (J. G. H.)
ANNECY, the chief town of the department of Haute Savoie in France. Pop.
(1906) 10,763. It is situated at a height of 1470 ft., at the northern end of the lake of Annecy, and is 25 m. by rail N.E. of Aix les Bains.
The surrounding country presents many scenes of beauty. The town itself is a pleasant residence, and contains a 16th century cathedral church, an 18th century bishop's palace, a 14th-16th century castle (formerly the residence of the counts of the Genevois), and the reconstructed convent of the Visitation, wherein now reposes the body of St Francois de Sales (born at the castle of Sales, close by, in 1567; died at Lyons in 1622), who held the see from 1602 to 1622. There is also a public library, with 20,000 volumes, and various scientific collections, and a public garden, with a statue of the chemist Berthollet (1748-1822), who was born not far off. The bishop's see of Geneva was transferred hither in 1535, after the Reformation, but suppressed in 1801, though revived in 1822. There are factories of linen and cotton goods, and of felt hats, paper mills, and a celebrated bell foundry at Annecy le Vieux.
This last-named place existed in Roman times. Annecy itself was in the 10th century the capital of the counts of the Genevois, from whom it pa.s.sed in 1401 to the counts of Savoy, and became French in 1860 on the annexation of Savoy.
The LAKE OF ANNECY is about 9 m. in length by 2 m. in breadth, its surface being 1465 ft. above the level of the sea. It discharges its waters, by means of the Thioux ca.n.a.l, into the Fier, a tributary of the Rhone. (W. A. B. C.)
ANNELIDA, a name derived from J.B.P. Lamarck's term _Annelides_, now used to denote a major phylum or division of coelomate invertebrate animals. Annelids are segmented worms, and differ from the Arthropoda (q.v.), which they closely resemble in many respects, by the possession of a portion of the coelom traversed by the alimentary ca.n.a.l. In the latter respect, and in the fact that they frequently develop by a metamorphosis, they approach the Mollusca (q.v.), but they differ from that group notably in the occurrence of metameric segmentation affecting many of the systems of organs. The body-wall is highly muscular and, except in a few probably specialized cases, possesses chitinous spines, the setae, which are secreted by the ectoderm and are embedded in pits of the skin. They possess a modified anterior end, frequently with special sense organs, forming a head, a segmented nervous system, consisting of a pair of anterior, dorsally-placed ganglia, a ring surrounding the alimentary ca.n.a.l, and a double ventral ganglionated chain, a definite vascular system, an excretory system consisting of nephridia, and paired generative organs formed from the coelomic epithelium. They are divided as follows: (1) Haplodrili (q.v.) or Archiannelida; (2) Chaetopoda (q.v.); (3) Myzostomida (q.v.), probably degenerate Polychaeta; (4) Hirudinea (see CHAETOPODA and LEECH); (5) Echiuroidea (q.v.). (P. C. M.)
ANNET, PETER (1693-1769), English deist, is said to have been born at Liverpool. A schoolmaster by profession, he became prominent owing to his attacks on orthodox theologians, and his members.h.i.+p of a semi-theological debating society, the Robin Hood Society, which met at the ”Robin Hood and Little John” in Butcher Row. To him has been attributed a work called _A History of the Man after G.o.d's own Heart_ (1761), intended to show that George II. was insulted by a current comparison with David. The book is said to have inspired Voltaire's _Saul_. It is also attributed to one John Noorthouck (Noorthook). In 1763 he was condemned for blasphemous libel in his paper called the _Free Enquirer_ (nine numbers only). After his release he kept a small school in Lambeth, one of his pupils being James Stephen (1758-1832), who became master in Chancery. Annet died on the 18th of January 1769.
He stands between the earlier philosophic deists and the later propagandists of Paine's school, and ”seems to have been the first freethought lecturer” (J.M. Robertson); his essays (_A Collection of the Tracts of a certain Free Enquirer_, 1739-1745) are forcible but lack refinement. He invented a system of shorthand (2nd ed., with a copy of verses by Joseph Priestley).
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