The molecules of iron, becoming incorporated in the now thick and viscous oil or imbedding themselves in the bearing, act as an abrasive; the black surface is removed, making the pivot again bright, but "ringed." The molecules of iron, uniting with the molecules of oxygen which exist in the oil in its oxidized state, forms ferric oxide.

Ferric oxide is known as colcothar, English-Roth, rouge, crocus, etc.

The above theory is advanced by the author for what it may be worth, as it seems to explain this curious phenomenon.

FOOTNOTES:

[11] Saunier. Watchmakers' Handbook.

CHAPTER V.

THE PROPERTIES AND RELATIVE VALUES OF LUBRICANTS IN HOROLOGY.

~62. Lubrication~ has for its objects, both the reduction of friction and the prevention of excessive injury from wear; and the mechanician resorts to the expedient of interposing between the rubbing surfaces a substance having the lowest possible coefficient of friction with the greatest possible capacity for preventing wear.

The valuable qualities of lubricants are determined by their power of reducing friction, and by their endurance as well as that of the surfaces on which they are used. The amount of frictional resistance to the motion of machinery is obviously determined by the character of the lubricating material.[12]

~63. The Animal Oils~ have had a wide and varied application in general machinery, and much testimony might be produced to show the superiority of any one kind over all the other kinds. Each variety has some particular property which some of the others may not have to such a degree.

~64. Porpoise Jaw Oil[13] and Blackfish Melon Oil~ have certain good qualities which have made them very popular, particularly on this side of the Atlantic. When properly refined (4-6) they are no doubt very suitable for the work of reducing friction in small and delicate mechanism.

~65. Sperm Oil~ (7) had been used to some extent as a lubricant for time-keeping contrivances; in fact, many tower clock experts still employ it on the heavier bearings. A. Long, writing to the British Horological Journal, describes a trip to the Arctic regions in 1814 and 1815, in which he states that a certain portion of the sperm oil they obtained never congealed, which they preserved and applied to their chronometers, and thus kept them going through the winter.

Others have experimented with it, and it was at one time largely used; while some tower clock makers claim that they find it satisfactory. It is, however, open to the objection that it would produce serious variation when used in time-keeping mechanisms, as its _viscosity varies greatly with varying temperatures_ caused by the alteration of the spermaceti it contains, thus causing sudden fluctuations of its coefficient of friction (81). It also absorbs oxygen rapidly when it is exposed to the air and loses quality seriously, gradually becoming "gummed" or resinous. A gain of two to three per cent in weight in twelve hours when exposed to the air at 140 F. (60 C), is caused by this absorption of oxygen (10).

~66. Bone Oil~ (8) has been widely used both in this country and in Europe, and possesses some good qualities, not the least of which is the property of resisting evaporation and oxidation.

~67. Neatsfoot Oil~ (9) has been largely used, especially in Europe. The writer regrets that he has not procured samples in order to ascertain its relative value.

~68. Olive Oil~ (10) has at least one good quality. It is one of the most perfectly non-drying of all the oils, resisting both oxidation and evaporation (24). But it is next to impossible to entirely remove its acid qualities, small traces of which remain after the most thorough treatment. It is also liable to decomposition, generating acids even after refinement.

~69. Mineral Oil~ (11) has been used as a lubricant for time keeping mechanism; but as there are so many varieties on the market, each differing from the others and possessing properties peculiar to itself, and as many have made experiments which have not demonstrated that such oils possess all the essential qualities of a perfect lubricant in horology, the author believes that the abundance of kinds and qualities of mineral oils has in the past been more or less confusing to the majority of those who have experimented; and believes further, that if the proper kind and quality of such oils had been used, all that could be desired in a lubricant would have been shown to have been contained therein.

Past experience has shown that many lubricants remained for years unused for special purposes to which, when tried, they were found specially adapted.

Though E. Rigg was probably in error in the matter previously discussed (44) his otherwise excellent lecture contains the following:--[14]

"But there is another subject that has a still closer bearing on friction as met with in time keeping instruments, and I cannot bring my lecture to a close without reference to that most fruitful source of trouble to the watchmaker--oil. Breguet, a very famous horologist, and D'Arcet, an equally celebrated chemist, worked together at this problem and what was the result? They produced an oil that was, according to their theory, perfect; but when applied to watches it proved to be worse than the ordinary oils of commerce. Since their day the chemistry of oil has not made much progress, and the methods recommended for testing oil are still very ineffectual. The only test of any use is actual trial for a long period, and under varying conditions as to temperature, nature of atmosphere, etc.; and there are several oils on the market more or less satisfying the required conditions. So far as my knowledge goes, however, all are liable to dry; and this prompts me to draw your attention to a lubricator that has come into use for heavy machinery in recent years, in the hope that it may afford a suggestion for the improvement of watch oils. I allude to the mixture of certain kinds of mineral oil with an oil that has a tendency to dry. Even a small percentage is a.s.serted to entirely check this tendency and the resulting mixture is said to have the property of not in any way acting on or damaging the metal to which it is applied. The thickness, or 'body,' is made to vary according to the pressure to which the oil is subjected. *

* * * Would it be oversanguine to hope that some such mixture, prepared from perfectly pure materials, might help even the chronometer maker to secure more uniform rates? Absolute freedom from acidity means a reduction of such electrical action as may occur at the pivots, and, therefore, a greater permanency of the oil from this point of view."

~70. Neutral Oil~ (14) seems to be especially adapted for use in horology.

Used in a pure state, or mixed in variable quant.i.ties with a good animal oil, it can readily be made to fulfill the various conditions required in all parts of watches, chronometers, mantel and tower clocks.

It is usually sold as such, but sometimes under the names "liquid paraffine," "glycoline," "albolene," etc., while "solid paraffine,"

"white cosmoline," "solid alboline," are the names given to the thick butyraceous ma.s.s from which neutral oils are made. Sometimes this substance, as well as the liquid paraffine, is medicated or perfumed; but it is hardly necessary to state that when thus treated it is unfit for use in horology.

~71. The Properties of Neutral Oil~ are stated to be:[15]

"It is a clear oily liquid, having a specific gravity of not less than 0.840 and boiling not below 360 C. (680 F.). It should be free from colored, fluorescing, and odorous compounds.

"When heated for a day by means of a water bath, the paraffine should not become dark colored, and the sulphuric acid should become only slightly brownish. Metallic sodium treated in a similar manner should retain its metallic l.u.s.tre. Alcohol boiled with paraffine should not have an acid reaction."

~72. The Properties of Solid Paraffine~ (13) are given as follows:[16]

"The melting point of commercial paraffine varies much. Obtained from the residuum of petroleum distillation it is usually 43 C. (109.4 F.), or somewhat higher."

The acid and metallic sodium tests given for liquid paraffine will apply to the solid paraffine.

~73. The Value of a Lubricant~ _as_ a lubricant is independent of the market price; and it is at a maximum, according to Thurston, when it possesses the following characteristics:

1. Enough "body," or combined capillarity and viscosity (82), to keep the surfaces between which it is interposed from coming in contact at maximum pressures.

2. The greatest fluidity consistent with the preceding requirements, i.

e., the least fluid friction allowable.

3. The lowest possible coefficient of friction under the conditions in actual use, i. e., the sum of the two components, solid and fluid friction, should be a minimum.

4. A maximum capacity for receiving, transmitting, storing and carrying away heat.

5. Freedom from tendency to decompose or to change in composition by gumming or otherwise, on exposure to the air (79) while in use.

6. Entire absence of acid or other properties liable to produce injury of materials or metals (77) with which they may be brought in contact.

7. A high temperature of vaporization and a low temperature (83) of solidification.

8. Special adaptation as to speed and pressure of rubbing surfaces under which the unguent is to be used.

9. It must be free from grit and from all foreign matter.

The author will add that for use in horology:

10. It must possess a minimum variation of viscosity (84) in varying temperatures.

The writer can see no reason why a mineral oil which has been properly refined _and of the proper consistency_, either alone or mixed with animal oil, could not be used to great advantage in horology. Indeed, the possibilities in this direction seem to be so pregnant with promises of good results that some s.p.a.ce will be devoted to the matter.