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Watchmakers' Hand Book

Part II,
MATERIALS EMPLOYED IN HOROLOGY
Page 9

SILVER.

      114. This metal in an unalloyed state is too soft for use in horology; its principle use is for cases, and as a constituent of solders.

      Houriet made watch wheels of an alloy containing 2 parts silver to 1 part 18-carat gold, and he affirmed that this alloy became polished at the acting surfaces of the teeth. Jurgensen states that chronometer escape-wheels made of this alloy, carefully hammered, do not require oil at the points of their teeth.

      Dumesnil proposed an alloy of 2 parts copper, 1 part silver, and 1 part zinc, all perfectly pure. Lecocq make chronometer balances in which the brass was replaced by pure silver deposited on the surface of the steel by electrolysis, thus avoiding the use of fire. The compensation is said to have been very efficient.


ALUMINIUM AND ALUMINIUM BRONZE.

      115. Aluminium is an extremely light elementary body, having a density of only 2.56; with equal bulks, therefore, it will weigh only about as quarter as much as silver. As its capacity for heat is very great, this metal is observed to heat or cool more slowly than other metals.

      Pure, or in a slightly alloyed state, it has not been used in horology, except for pendulum rods and large hands in regulator clocks; in short, it can be employed where lightness is the principal quality in view.

      It is extremely ductile. The presence of 1/100th part of bismuth, however, renders the metal somewhat brittle, and it develops cracks under the hammer. Traces of iron also decrease its malleability.

      An alloy of 5 parts silver and 95 aluminum can be as easily worked as the pure metal, but is harder and takes a better polish.

      We would add a curious observation of M. Redier: After passing a piece of aluminium several times through the draw-plate, he observed that the elongation had only occurred at the surface; for on cutting the wire at different points, he noticed that, throughout a portion of the length, the metal was hollow, a very fine capillary tube being thus formed.

      116. Aluminium Bronze is an alloy of aluminium with copper. An alloy of 5 parts of the former to 95 of the latter has a beautiful golden color, but if the proportion is changed to 10 and 90 parts respectively, we obtain the most serviceable and the most easily worked alloy.

      This bronze can be forged at a cherry-red heat, and even near its melting point; and its thickness can be reduced to a very small amount under the hammer. It is easily filed and turned, but does not possess any special advantage over brass, which is less detrimental to the file; the density is 7.7, very little below that of brass, 8.4.

      It appears from a considerable number of experiments that it might be used with advantage for the bearings of axels that rotate with high velocities. It resists wear better than any other metal. In the experiments made by Foucault to demonstrate the rotation of the earth by means of the pendulum, he found that an aluminum bronze wire lasted for the longest period. Its tenacity is equal to that of iron. It has been shown that slide-bars of locomotives made of this bronze resist wear twice as long as those formed of the ordinary bronze. There would then be an advantage in using it for the bearings of foot-lathes, etc.

      Grossman asserts that lever escape-wheels of this metal have proved satisfactory, and he makes the following observation on the subject. If aluminium bronze be reduced to three-fourths of its original thickness by hammering, it will begin to crack. This can be prevented by heating to a red heat and plunging into water; it can then be again reduced by one-forth of its thickness from 2.5 millimeter to 0.2 millimeter, and the metal resisted for a long period repeated flexures backwards and forwards; and he observes that no other metal, after being so much compressed, would possess the same marvelous degree of tenacity.

      In order to obtain aluminium bronze of the best quality, the copper should be absolutely pure, and, in the manufacture, the alloy must be melted and forged two or three times in succession, as by this means the strength and tenacity are increased, and the metal can be more easily worked.

      The beautiful golden color possessed by certain of these bronzes when polished, has caused them to be used for cheap watch-cases, but they always tarnish at those parts that are not subject to daily wear.


MERCURY.

      117. This is the only metal liquid at the ordinary temperature; it solidifies at -40° C. (10° F.). It possesses a high metallic lustre, resembling silver, but with a slightly bluish tint, and does not oxidize at ordinary temperatures.

      Mercury alloys with many other metals, forming amalgams, and as small a quantity as 1/40th per cent of lead suffices to entirely alter its character. The presence of such traces can be easily detected by the liquid wetting glass or china, and therefore forming a tail when a vessel containing it is tilted.

      The commercial metal is rarely pure, but the greater portion of the lead, tin, bismuth or copper, by which it is contaminated, can be removed by distillation. The most convenient method consists, however, in agitating the metal with either dilute nitric acid, a solution of mercurous nitrate, strong sulphuric acid, a solution of corrosive sublimate or of perchloride of iron, and subsequent washing with distilled water. When mercury is only contaminated with mechanical impurities, they can be very effectually removed by agitating with powdered loaf sugar.

      This metal has many uses in the arts, for the construction of thermometers, barometers; for plating, etc.; in horology it is used for compensation pendulums, and has also been occasionally used for compensation balances.


PLATINUM

      118. This elementary body is almost as white as silver, takes a brilliant polish, and is highly ductile and malleable. It is the heaviest of the ordinary metals, the least expansive when heated, and has a breaking strain of 40 kilo. per sq. mm. section (56,500 lbs. per sq. inch.).

      Platinum is infusible, except at the high temperatures attainable with the oxy-hydrogen blowpipe. At a white heat, however, it softens, and can be forged and welded. It is unacted upon by the air at any temperature, and is insoluable in acids, except aqua regia (155), although acted on by certain alkalies.

      This metal is used in the construction of scientific instruments, and for objects that are exposed to the air, as, for example, sun dials. Alloyed with irridium, (a rare metal of the same group) it possesses an excellent and unalterable surface for fine engraving, as the scales of astronomical instruments, etc. This alloy has also been adopted for the construction of international standards of length and weight.

      Platinum is much employed for chemical apparatus, in consequence of its being unacted on by acids, and its nonliability to melt in ordinary furnaces. Both the pure metal and its alloys with silver have been employed in the form of wire for bushing the pivot-holes of watches, and in sheets for cutting out cocks and wheels, but the results obtained were not as good as with good brass. As a rule, such wheels are found to occasion a rapid wear of pinion leaves.

      Attempts have also been made to construct balance-springs of this metal, but we are informed that they were not found to possess any sufficient advantages.

      It is not advisable to heat platinum in a spirit-lamp or Bunsen burner; the naked flame is objectionable, because, being charged with a certain amount of carbon, it deteriorates the metal.


PALLADIUM.

      119. This metal resembles silver rather than platinum, and is almost as infusible as the latter metal. It has a density of 12.5. When heated in contact with air it becomes blue, owing to the formation of an oxide. It possesses the remarkable power of absorbing (or occluding) about 900 times its own volume of hydrogen, if attached to the negative pole of a battery in acidulated water; its bulk is increased slightly by this charge, and on expelling the gas by the aid of heat, the metal shrinks to less than its initial dimensions. Palladium is useful for the graduated scales of scientific instruments, since it is not discolored by sulphurous acid. It forms alloys with most of the metals and some of these can be hardened like steel. If 100 parts of steel be alloyed with 1 part of this metal, the resulting alloy is said to be excellent for making scientific instruments, and an alloy of 24 parts palladium, 44 silver, 72 gold, and 92 copper has been recommended for use in horology.

      M. Paillard, of Geneva, has introduced balance-springs made of an alloy, whose composition is not given, possessing the following advantages: they are non-magnetic, their tenacity is considerable, are not tarnished by the air, sulphurous acid, or sea water; nor are they distorted by heating, and, on cooling, they recover their original elasticity, which is equal to that of steel hardened and tempered to a blue color. The co-efficient of expansion of this alloy is rather less than that of steel.


CHARACTERISTIC PROPERTIES OF ALLOYS.

      120. DENSITY. This is sometimes rather greater and sometimes less than that deduced from the densities of the constituent metals,* but no exact law has been discovered in regard to this question.

      * The theoretical density of an alloy, on assumption that in alloying the metals do not contract or expand, is obtained by dividing the percentage proportion of each constituent metal by its density, adding the products so obtained together, and dividing their sum into 100.

      Hardness, Ductility, Tenacity. Alloys are usually harder, more brittle, and less ductile and tenacious than the most ductile and tenacious constituent metal.

      elasticity. The co-efficient of elasticity of an alloy generally approximates closely to the mean of the coefficients of the constituent metals.

      Expansion. The co-efficient of linear expansion of an alloy, that is to say, the number representing the proportional part of its lenth by which it increases for each degree rise of temperature, may be approximately estimated as follows: multiply the linear co-efficient ofeach constituent metal by the percentage of it present in the alloy, and divide by its density. Add together the several numbers thus obtained. Multiply this sum by the density of the alloy (which must be experimentally determined) and divide by 100. The resulting figure is the required linear co-efficient (122).

      Fusibility. Alloys are always more fusible than the least fusible of their component metals, and often more so than any one of them.

      Oxidation. As a rule, the air acts with less energy on alloys than on their constituent metals, There are, however, cases in which the converse is the case.

      Action of acids. This is generally similar to the action on the predominating metal.

      Observations. Alloys formed of metals that differ materially in density are rarely homogeneous, especially if they have been allowed to cool slowly. It is, then, essential that they be thoroughly stirred and cooled rapidly. It is for this reason that alloys are frequently poured out on a flagstone to cool, or that they are compressed after pouring, whereby the formation of crystals is prevented.

      121. Metals and alloys. The following table gives the more important physical properties of the metals and alloys generally met with, and will be found useful for reference. The precise meaning of each number may be gathered from the notes in paragraph (122).


Table of Metals and Alloys.

      122. Notes on the foregoing table. For a complete explanation of the several properties of metals and alloys that are enumerated in the above table, the reader must be referred to works on mechanics and physics, but the following explanatory notes are necessary.

      The number in brackets after the name of each metal, etc., refers to the article in which it is considered.

      The specific gravity of a substance is the ratio of the weight of a given bulk of that substance to the weight of the same bulk of water at a definite themperature. The numbers here given can only be regarded as approximations, as the specific gravity varies greatly with the state in which a body exists, the hammering it may have been subjected to, etc.

      Degree of hardness is ascertained by means of the following standard series, observing which of them scratches the body under examination and which it is capable of scratching.

  1. Talc
  2. Gypsum
  3. Calc-spar
  4. Flour-spar
  5. Apatite
  6. Felspar
  7. Quartz
  8. Topaz
  9. Saphire
  10. Diamond

      Linear expansion. These co-efficients represent the extension in length that several substances undergo when heated: the first column for each degree Fahrenheit and the second for each degree Centigrade (Celsius). The extension is given per unit of length; thus, 1 inch of copper at 32° F. will become 1 + 0.0000102, or 1.0000102 inch at 33° F.; and 1 + 30 X .0000102, or 1.000306 at 32 + 30 or 62° F.

      Superficial expansion may be obtained by multiplying he linear co-efficient by 2, and cubical expansion by multiplying the same number by 3.

      As in the case of specific gravity, these data, as well as those in succeeding columns, can only be regarded as approximations, depending on the condition of the metal, etc.

      Specific heat is the amount of heat required to raise the temperature of a substance one degree (the Centigrade scale being here adopted), that required for the same weight of water being taken as unity. The corresponding numbers on the Fahrenheit scale can be deduced from those here given by multiplying by 5 and dividing by 9, then adding 32.

      The melting points are given on Fahrenheit's scale and can only be regarded as approximate on account of the difficulty experienced in determining these high temperatures. Different observers often vary by two or three hundred degrees in their estimates.

      Conductivity for heat and electricity are given in reference to that of silver, which is called 100. It surpasses all other known metals in both these properties when chemically pure, but a trace of impurity has a very prejudicial influence on them.

      It will be observed that in many cases the conductivities have not been determined, a remark that applies to other columns of the table.

Submitted by: Samuel Kirk (##)

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