Vol. XXm. No. 6.] 



'OPULAR SCIENCE NEWS. 



85 



Practical Cljoujistry and tlje ^rts. 



MERCURY. 



Only two elements are liquid at ordinary 

 temperatures, mercury and bromine, and the 

 former is the only one of a metallic nature. 

 It is certainly a strange sight to see a metal in 

 a perfectly liquid state, resembling melted 

 lead or silver, anil jet perfectly cool and 

 harmless to the touch. Probably from its 

 unique nature, this metal was a favorite sub- 

 ject of study with the old alchemists, and 

 their futile efforts to "transmute" it into gold 

 or silver are well known. 



Unlike other liquids, also, pure mercury 

 will not wet or adhere to most solids, such as 

 glass. This property renders it of the utmost 

 value in the manufacture of thermometers, 

 barometers, and other philosophical instru- 

 ments. It may be handled like so much 

 water, but always eludes the grasp, and slips 

 away from the fingers like the nimble god 

 from which it takes its name. When brought 

 in contact with nearly all other metals, how- 

 ever, it unites with them, wetting their sur- 

 face like so much water, and forming an im- 

 portant class of compounds known as amal- 

 gams. Iron and platinum are the only metals 

 it will not corrode, and it adheres even to the 

 latter metal. It may, however, be kept in- 

 definitely in iron vessels. When impure 

 from the presence of other metals, it loses its 

 fluidity in a greater or less degree, and will 

 adhere or leave a stain upon glass or porce- 

 lain, when brought in contact with it. 



Mercury has a high boiling point (663° F.), 

 and an equally low freezing point ( — 39° F.) 

 — a point often reached in the winter season 

 in the arctic regions. It can also be frozen 

 artificially by pouring it upon a mixture of 

 solid carbonic dioxide and ether, making a 

 very striking lecture experiment. The solidi- 

 fied mass resembles closely a piece of lead or 

 zinc, and does not feel as cold to the touch as 

 its temperature would indicate. In its chem- 

 ical relations, it is closely allied to copper and 

 silver, although, as is olten the case, tiiere is 

 but a slight physical resemblance between 

 them. It is slightly volatile at ordinary tem- 

 peratures, like water, and a piece of gold-leaf, 

 placed near the surface of the metal, will 

 soon show the presence of the \aj5or by be- 

 coming amalgamated with it. 



The ores of mercury are found most 

 abundantly in Austria, Spain, China, and 

 California. It occurs sparingly in the native 

 or metallic state, but the principal ore is cin- 

 nabar, or mercuric sulphide (Hg.S.) The 

 ore is reduced by simply roasting it in a kiln, 

 and condensing the vapors in a series of 

 chambers. The sulphur burns, and passes 

 oft' as sulphurous anhydride, wliile the mer- 

 cury vapor is condensed and Hows ofl' into 

 vessels placed to receive it. In Spain, the 

 condensation is efiected in earthen vessels. 



called aludels, the name having come down 

 as a relic of the times when the Arabians car- 

 ried on the industry in that countrj'. In 

 another process, the cinnabar is distilled in 

 cast-iron retorts, with lime, when the sulphur 

 is left in the residue as sulphide of calcium, 

 and the mercury passes over. 



The uses of mercury are very numerous. 

 Besides being used in the manufacture of 

 scientific instruments, large quantities are 

 consumed in the manufacture of inirrors. 

 Pure mercury will not adhere to glass, so an 

 amalgam is made by spreading a sheet of tin- 

 foil upon a level table, rubbing it over with 

 mercury, and then carefidly sliding a plate of 

 clean glass upon it. The amalgam, which 

 contains about one part of merciu-y to four 

 parts of tin, adheres strongly to the glass, 

 and, in a few days, becomes hard, so that the 

 glass can be lifted up and removed. Much 

 skill and experience are necessary to carry out 

 the operation successfulU'. Eftbrts have been 

 made to substitute silver or platinum for the 

 mercmy, but, so far, such mirrors have been 

 found inferior to those made b\' the mercurial 

 process. 



An amalgam of sodium and mercury is 

 used in the extraction of gold and silver from 

 their ores, and is a useful laboratory reagent, 

 while amalgams with gold, silver, and plati- 

 num, are used by dentists in filling decayed 

 teeth. 



Of the salts of mercury, the mercuric sul- 

 phide, or vermilit)n, is the most important, 

 being largely used as a pigment. The natu- 

 ral sulphide, cinnabar, varies in color from 

 black to bright red, but the finest qualities are 

 prepared artificially, bj- various processes, 

 both wet and dry, the brilliancy of the color 

 depending upon modifications of the processes, 

 which are kept secret by the diflerent manu- 

 factiu-ers. The best vermilion is still pre- 

 pared by the Chinese, by slow and tedious 

 methods, which no other race would have the 

 patience to carry on. 



Certain salts of mcrcurj' are valuable medi- 

 cinal agents, but their action is so powerful 

 that great care must be used in their adminis- 

 tration. Mercuric chloride, or corrosive sub- 

 limate, (HgCl-.)), is one of the most powerful 

 poisons known, while mercurous chloride 

 (HgiCli) is the well-known calomel, so ex- 

 tensively prescribed by physicians. The dif- 

 ference in the physiological action of these 

 two closely allied substances is hard to ex- 

 plain. Metallic mercury, when minutely 

 divided by triturating it with chalk, forms a 

 mass which has no metallic appearance, al- 

 though it is simply a mechanical mixture, and, 

 probably, no chemical change takes place. 

 This mixture is known to physicians as gray 

 powder, or blue pill. In former times, several 

 pounds of liquid mercury were sometimes given 

 atone dose, as a heroic remedy for constipation, 

 presumably to act on the principle of hydro- 



static pressure. Fortunately, in these days 

 the science of medicine has advanced beyond 

 such barbarous methods. 



The chemical symbol of mercury is Hg, 

 a contraction of the Latin hydrargyrum, 



meaning watery silver. 



+♦• 



[Original in The Popular Science News.] 



PREVENTION OF MAGNETISM IN 



WATCHES. 



BY PROFESSOR W. M. STINE. 



One peculiarity of modern progress, is the extent 

 to which advancement in one direction, exerts an 

 influence in others which before had seemingly no 

 connection. This is well illustrated in the recent 

 improvements in watch construction. Owing to 

 the very general employment of the dynamo, motor, 

 and other electrical appliances, a pressing demand 

 is arising for a watch which cannot be affected by 

 magnetism; and, as usual, necessity, furnishing an 

 incentive to invention, is conquering the difficulty 

 which is now found to exist in the usual form of 

 watches. 



Those who have not given especial attention to 

 the construction of a watch, are apt to regard it as 

 a rather intricate piece of mechanism. This is not 

 the case, as it is in principle quite simple, consisting 

 essentially of a train of five wheels and a governing 

 attachment. 



In this train there is, first, the largest wheel in 

 the watch, the barrel, a flanged wheel, which con- 

 tains the main-spring. This power wheel is geared 

 into the centre wheel, whose staff, or arbor, carries 

 the minute-hand. The centre wheel, in turn, actu- 

 ates what is called the third wheel, whose function 

 is simply to reduce the speed of the next wheel in 

 the train, termed the fourth, to whose staff" is 

 attached the second-hand. This connects directly 

 to the last wheel, the fifth, or escapement, to which, 

 by means of a lever, is attached the governing appa- 

 ratus, and it is in this latter that we have what may 

 be considered the vital part of the mechanism, — 

 since the time-keeping qualities depend almost 

 wholly upon it; and it is also the portion to which 

 the time and attention of the maker is chiefly given, 

 and whose construction and adjustment largely de- 

 termines the cost of the movement. 



The governing of a watch, to make it a time- 

 keeper, is accomplished, primarily, through the bal- 

 ance and hair-spring; the balance wheel playing 

 the part of the pendulum in a clock, — so that it may 

 be regarded as an oscillating pendulum, — while the 

 hair-spring takes the place of the pull of gravity. 



Into the coarse teeth of the escapement wheel, the 

 pallets carried by the fork play alternately. The 

 fork, being in direct connection with the balance 

 staflF, is kept in vibration b^- the combined action of 

 the main and hair-springs. The free end of the 

 hair-spring is attached to the balance staff, and coils 

 and recoils with its reciprocating motion. As the 

 hair and main-springs act against each other, the 

 recoil of the main-spring delivered by the escape- 

 ment, turns the balance through a portion of a rev- 

 olution and coils the balance-spring. When all the 

 energy of the impulse of the balance is spent in 

 coiling its spring, it pauses, and the elasticity of the 

 hair-spring in recoil, moves the balance in the oppo- 

 site direction to its first position. 



This, in brief, is the mechanism and action of the 

 ordinary watch. To control this, so that it may 

 run accurately and be relied upon under widely 

 varying conditions, is, however, a difficult task. 

 The main-spring, it must be remembered, simply 

 furnishes the power to keep the works moving, hav- 

 ing nothing to do with the rate of the watch; this 

 can be affected only in the controlling combination 



