Page images
[ocr errors]


most important variety of the mineral is a "cupreous iron method and the calorimetric method were both cmployed pyrites," which for many years past has been wrought on by Pouillet for the accurate measurement of high temperan enormous scale in Spain and Portugal. This ore seems atures before 1836. to be an intimate mixture of iron pyrites with a small $ 2. The indications obtained by any of the numerous quantity of copper pyrites, the proportion of metallic copper methods which have been suggested are, as a rule, expressed being generally less than 3 per cent. Notwithstanding in terms of Centigrade or Fahrenheit degrees. This assignthe poorness of the ore, the copper is profitably extracted ment of numbers presupposes not only a definition of temby wet processes. There is also present a small quantity of perature by which the size of the degree is determined but silver (20 to 35 dwt. per ton), with a trace of gold. The also a physical law which gives the relation between the deposits of this cuprcous pyrites are of enormous magni- measured interval of temperature and the standard degree. tude, and occur at the junction of porphyritic rocks with The various definitions of the standard degree that might clay-slate of Devonian age. The principal Spanish mines he employed will be found in the article Heat, secs. 12, are those of Rio Tinto, Tharsis, and Calañas in the province 24, 25, 30, 31, 32; and in sec. 35 of the same article thé of Huelva; whilst the most important of the Portuguese definition of the absolute thermodynamic scale of tempermines is that of San Domingos in the province of Alemtejo. atures is given. In the same article (sec. 38) it is shown There is ample proof that some of these pyritic deposits that the “absolute temperature” of à liquid in thermal were worked by the ancient Romans.

equilibrium with its wn vapour under a pressure p may The quantity of cupreous and other iron pyrites imported be obtained from the formula into Great Britain during the year 1883–principally from

P(1 -0.012 Spain and Portugal, but partly from Norway and elsewhere - was 601,288 tons, of the declared value of £1,356,083.

t=t.e:P) But this quantity had been exceeded in several previous where p is the density of the vapour, por that of the liquid, years, notably in 1880 and 1877. The quantity of iron k the latent heat per unit-mass of the rapour corresponding pyrites raised in the United Kingdom in 1883 amounted to the saturation-pressure p.

to the saturation-pressure p. The dynamical equivalent to 27,672 tons, of the value (at the mine) of £17,167. of heat is represented by J. We have therefore the com

See Iron, vol. xiii. pp. 280, 288 ; Copper, vol. vi: 1: 3.17.; MUplete theory of what may soon become a practical method
CASITE, Vol. xv. p. 532; and MINERALOGY, vol. xvi. PP. 390, 393.
For details of the Rio Tinto pyrites, see al Treatise on Orc-Deposits,

of expressing temperatures in the thermodynamic scale. by J. Arthur Phillips, 1881.

Sir W. Thomson, in the article mentioned (sees. 39-45). PYRMONT. See WALDECK.

has described arrangements for measuring the pressure of PYROMETER, an instrument for measuring high the saturated vapours of various liquids which will give temperatures. As long ago as 1701, in a paper published that measurement in a thoroughly satisfactory manner up anonymously in the Philosophical Transactions, Newton to, at any rate, some 600° C. For the higher temperasave the results of attempts to estimate the temperature tures mercury is the liquid employed. There are, however, of red-hot iron by noting the time it took to cool to an some experimental data still wanting before the formula observed temperature, assuming what has since been called quoted above can be applied to the numerical calculation Newton's Law of Cooling. The numerical results are of the temperature. These are (1) the density p of the given in terms of the degrees of a linseed-oil thermometer saturated vapour corresponding to the series of pressures

, constructed by Newton. Its zero was the temperature of and (2) the corresponding latent leat k of vaporization. melting ice and its second fixed point the normal temper- These constants have not yet been actually observed. ixture of the human body, denoted by 12'. About the same Instruments such as those figured in the article cited time Guillaume Amonton in Paris madle somewhat similar can, however, he employed with convenience and accuracy attempts to determine the tomperature of the red-hot end as continuous intrinsic thermoscopes, whose indications of an iron bar, using for reference a rudimentary air-thermo- can supply a numerical measure of temperature after an meter—the first of its kind in which the variation of empirical graduation. When ilsend thus they possess the atmospheric pressure was allowed for. Since the middle enormous advantage that the pressure of the saturatel of the last century the different methods and instruments vapour at a definite temperature is perfectly detinite, so suggested for measuring high temperatures have been very that a single observation of the pressure is all that is nunerous, in fact the variation of almost every physical necessary to determine the temperature, and the instruproperty of substances which alter with change of temperament can be easily arranged, so that his observation is ature has been utilized for this purpose. Measurements practically a very simple one. The pressure of mercury of the increase of pressure produced in a quantity of gas vapour has already been determined by Reynault for while its volume remains constant or of the increase of temperatures up to 150. I thermoscopic method of volume at constant pressure, of the heat given out by a pyrometry which is very similar to the alure was solicam mlak of metal in cooling to an observed temperature, of besteed by Lamy? Hle proposed to measure the porra nire the expansion of a metal or graphite bar or of a mass of of carbonie-ide il cas vissociated from calcium carbonate. clay are those which have been most frequently employed: There is experimental evidence to low that the forestare Lui, besides these, the change in the electrical resistance of the dissociated gas is definite at a definite temperaof wire, the saturation-pressure of the steam of various ture. The recombination of the divoriateed aan with the fiquids

, the pressure of gas dissociated from various soliels, solid is, however, a low process, and the method has the eletromotive force of a thermo-electric couple, the been pronouncul liv Weinhell to love practically unsatisbrn-ity of the vapour of a liquid, the change of shape of factory.

compound spiral of different metals, have been used, - $ :). Gues Pill. JO1011". weit 191., Telipe I sen the alteration in the wave-length of a note of given

note of given tur s by the E. Nire wherliin. Pirmare ch has lwen suggestel as capable of being made use - Temperatures MAV lepored in the alorite thin for pyrometric purposes.

For reasons which will lies dynamic scale lig ihe ninthared of the con- tlırmazlietet, given below, the numerical results obtained by one or

which is available for pr. personat vry high her of the numerous forms of the gas-thermometer hare temperatures. It has buen hound that the indications a more detinitely intelligible value. The gas-thermometer 7:07,03 RW..., lxi.s. p. :347.

Pysyrri-!! Vif-:hr," P. :1 11.16 I "Rala Graluum Caloris," in Phil. Tans., xxii. }', $21.

of a nitrogen or hydrogen gas-thermometer, whether it is | In like manner v100 – V, may be taken from a table of the
arranged to show the increase of pressure at constant coefficients of expansion of gases. The different methods
volume or the increase of volume at constant pressure, give which have been suggested for the employment of this
for the temperature numerical results which are practically property of gases to measure high temperatures are very
identical with the corresponding numbers on the absolute numerous. We give details of a few of them.
scale. It follows, therefore, that any two gas-thermo (1) The Constant- Pressure Method.—The following is a very
meters, if similarly graduated, would give identical indica- simple and practical plan of employing the method for obtaining a
tions for the same temperature, no matter whether or not reading of the temperature. A glass or porcelain bulb, provided
they are filled with the same kind of gas and whether or

with a fine neck, is very carefully dried and filled with perfectly

dry air ; it is then exposed to the source of the heat whose tempernot the quantities of the gases are such that the pressure in ature is to be investigated in such a manner that the point of the the two thermometers is the same at any one temperature. neck just projects from the furnace. When the equilibrium of This important property of gas-thermometers has been temperature is reached, the neck is hermetically sealed by a blowexperimentally verified by Regnault 1 by direct comparison pipe or oxy-hydrogen flame, and the bulb is witħdrawn and allowed

to cool, and weighed. The neck is then immersed in water or up to 350° C. of instruments filled with different gases and mercury and the point broken off. In consequence of the previous at different pressures. For these reasons the readings of expansion of the air the pressure in the interior is much less than a properly arranged gas-thermometer have justly come to the atmospheric pressure, and the liquid consequently enters the

bulb. be regarded as furnishing the standard of temperature, at

When so much has entered that the pressure is the same

inside and out (the difficulty of the comparative opacity of the any rate outside the limits of the freezing and boiling porcelain is not insurmountable), the end is closed by a small points, and indeed may now be regarded as the tempera- piece of wax, and the bulb removed and weighed, with the liquid ture standard for scientific purposes throughout the whole

it contains. The bulb is then completely filled with the liquid, range. The Kew standards are calibrated mercury-in-glass first weighings gives a value r', of formula (2), which only requires

and weighed a third time. The difference between the third and thermometers whose fixed points are repeatedly redeter-correction for the expansion of the envelope, while the difference mined. Such instruments will not agree exactly with the between the second and first weighings gives a value of the volume gas-thermometer except at the freezing-point and boiling- from which 2, and ?:00 can be calculated, using the known co-efficient point. Comparisons have been made between various

of expansion of air, and thus all the requisite data for the deter

mination of t are obtained. This method was used by Regnault5 mercury-thermometers and air-thermometers by Regnault 2 to determine the coefficient of expansion of air, and has since been and many others. The results obtained by different ob- lescribed as “a new pyrometer. servers are not entirely concordant; but it is needless In the process just described the volume of the residual gas is here to discuss them, for, whatever may be the divergence measured ; its pressure

, after cooling, may be measured instead, by between the mercury and air thermometers in the freezing- provided with a long tine neck, to the end of which a tap is fitted point and boiling-point, the method of measuring higher and so arranged that it can be easily connected with a manometer. temperatures by continuing the scale of a mercury-thermo- The bulb is exposed to the high temperature, the tap being left meter beyond those limits is altogether untrustworthy in open, and when the final temperature is reached the tap is closed

and the bulb allowed consequence of the very wide divergence between different

to cool; it is then mercury-thermometers at the same temperature, amount connected with the ing sometimes to 10° or more : at a temperature of 300°. manometer, and, if The air-thermometer readings must therefore be regarded the tap be a three

way ta!

drilled as as the standard at any rate for temperatures beyond the

shown in fig. 1, it is boiling-point.

easy to expel all the The general principle employed in the use of the gas- air from the bulb, side thermometer is as follows. Let be the pressure of a

of the manometer, Po

between the mercury mass of gas at 0° C., P 100 the pressure of the same mass of surface and the tap. gas at 100° C., the volume being the same, Pe the observed The residual pressure pressure of the same mass of gas at some unknown tem is then measured by perature t, the volume still remaining the same, then

the manometer.

correction is required Pt-- Po

Fig. 1. ..(1).

for the expansion of P100 - 1 100

the bulb and for the part of the connecting tube not exposed to the We require, therefore, three observations of the pressure, high temperature. Instead of measuring the volume of the residual two 4 to graduate the instrument and the third to measure gas in the manner thus described, Deville and Troost have pumped the temperature. If the thermometer has been filled with

the hot air out of the porcelain bulb by means of a Sprengel pump,

and measured the volume of air delivered by the pump. On this gas of a perfectly definite kind—e.., properly dried and plan a series of observations can be made at the same temperature, purified air, nitrogen, or hydrogen —and the containing a three-way tube with suitable taps serving to put the bulb altervessel has been previously thoroughly dried, the value of nately in connexion with a vessel to supply dry air and with the P200 may be obtained from tables, since 2100 = P.(1 + 100u), pump: Crafts and Meier" have obtained results by sweeping out where å is the tabulated coefficient of expansion of the

the air with a current of hydrochloric-acid gas, which was separated

from the air it carried by being passed through water. yas at constant volume. It is practically impossible to An instrument for observing the continuous variation of volume keep the volume of the gas constant in consequence of the of a gas at constant pressure is figured and described by Sir W. expansion of the envelope. A correction must be applied Thomson in HEAT (sec. 65). Arrangements have also been sugon this account, the value of which is derived from inde- gested by which the density of the gas at the high temperature

can be directly measured. Regnault 9 has described a hydrogen pendent observations of the expansion of the material of

pyrometer based on this principle suitable for measuring the the envelope. If the pressure of the gas be maintained | temperature of a porcelain furnace. A wrought-iron tube of known constant, and the volumes 2', '100, ?'be observed for the capacity is permanently fixed in the furnace'; it is filled with pure

dlry hydrogen by passing a current of the gas through it for some three temperatures ť, 100°, 0°, we have

time. The current of gas is then stopped, and after the gas has t ..(2).

attained the temperature of the furnace it is swept out by a current 2100 – 70 100

of dry air and passed over red-hot copper oxide. The water thus 1 "De la Mesure des Températures,” Mém. de l'Inst., xxi. p. 168. 2 Jém. de l'Inst., xxi. p. 191. 3 See Heat, sec. 26.

5 Mém. de l'Inst., xxi. Comptes Rendus, xc. 727, 773. 4 The two known temperatures at which the pressure is measured 7 (!. R., xc. 606. need not necessarily be and 100°, though these are often the most 8 Throughout this the term “density” is used whenever the convenient. The formula requires only slight modification to make mass of a unit of volume of a substance is referred to. it applicable when any two other known temperatures are avlopte.. O inn. de Chim., [3], lxiii. p. 39.



[ocr errors]
[ocr errors]


formed is collected in sulphuric acid tubes and its amount deter The continuous variation of temperature can be better observed mined by their increase in weight, and from this observation the by the constant-volume method. This method as used for temdensity of the hydrogen in the wrought-iron tube is calculated. peratures up to that at which glass softens (about 550° C.) was An arrangement of taps makes the observation a very easy one thoroughly investigated by Regnault,“ whose normal instrument when the apparatus is once set up. The formula (2) requires in is discussed under IIEAT, sec. 24. The difference of pressure between this case to be slightly modified. Thus let de, djvo, d, be the den the gas contained in the bulb and the atmosphere is measured by sities of the hydrogen at the temperatures ť, 100®, and 0° respect an open mercury-manometer. The barometric pressure must also ively, then for the same mass of gas m we have

be observed in order to obtain the values Pr, ??100, and P, respectively le de=V100 d100=v, do=m.

of formula (1). Various forms have been given to the manometric The formula therefore becomes

apparatus in order that the mercury may be brought at cach do - de 100-t

observation to the fiducial mark in the limb in connexion with the

bulb. Balfour Stewart's 5 has a screw adjustment. An instrudo - dio de

(3). 100

inent described by Colazza 6 is provided with an air-compression (2) The formula shows how the temperature of air in any experi- manometer, and thus the necessity of a separate observation of the inent may be determined when its density at that temperature is barometric height is dispensed with. Various other suggestions observed. It is sometimes more convenient to determine instead have been maile for securing the same object. the density of some vapour which at ordinary temperatures would The most convenient form of the instrument for general use is be a solid or a liquid, and to deduce from that observation the Jolly's (deseribed in Pougendorl's Jubelband, p. 82, 1874), and repredensity of air at the corresponding temperature. Thus, suppose sented in fig. 3. The two vertical tubes of the that the density 0c (expressed in grammes per cc.) of the vapour of manometer are connected by an india - rubber any given liquid or solid is observed, and that independent observa tube properly strengthened by a cotton covertions show that the specific gravity of the vapour, referred to air ing, and they can be made to slide vertically at the same temperature and pressure, is o, then we have de=0/0, up and down a wooden pillar which supports and, since d, and d 100 can be taken from tables, all the necessary them; they are proviiled with clamps for fixing quantities in equation (3) are obtained. It will be noticed that the them in any position and a tangent screw for value of o, the specific gravity of the vapour, is to be derived from fine ailjustment. The connexion between the independent observations. Apart from direct experimental evi- bulb and the manometer is made by means of denco in any particular case, there is the generally accepted theory, the convenient three-way tap described above. lased on the law of Avogadro, that the specific gravity of a gas or

The scale of the instrument is engraved on the vapour referred to lıydrogen at the same temperature and pressure back of a strip of plane mirror before silvering, is represented by half the number expressing the molecular weight and the divisions are carried sufficiently far of the substance of which the vapour is composed. For elements,

across the scale for the reflexions of the two with few exceptions (of which mercury is one), the ratio of the surfaces of the mercury to be visible behind Atomic weights gives the specific gravity referred to hydrogen at

the scale. Parallax can thus be avoided and the same temperature and pressure. At any rate, if there are suffi an accurate reading obtained without the necient data for us to regard o as known, we may evidently deduce cessity of using a kathetometer. In order to the value of do, and thus by formula (3) the temperature, from an allow for the expansion of the glass of the observation of or

reservoir a weight-thermometer bulb is supMercury l'apour.—Regnault? suggested the direct observation plied with the instrument, maile from another of the density of mercury vapour for the purpose of determining the specimen of the same kind of glass, and the temperature. The process is as follows. A quantity of mercury relative expansion of the mercury and the glass is place in a wrought-iron flask provided with a perforated lid as can thus be determined by the observer himshown in fig. 2, No. 1. The flask is then exposed to the temper- self. The volume of the air-bully and that of nture to be measured, and when thermal equilibrium is attained the the capillary tube and the small portion of

Fig. 3 small lid is slid along so that the neck is closed. The flask is then the manometer tube above the small beak of glass, the point of taken out and allowed to cool. The mercury is collected and which serves as the fiducial mark, are deterinined by the instruweighel; the volume of the flask is determined

ment-makers. The formula of reduction isand corrected for the expansion of the iron ;

II II, L. II 1

t=and these two observations determine the den


1 + at sity of mercury (in grammes per cc.) at the

where II is the pressure at the high temperature I, II, the pressure temperature in question. The specific gravity?

at the temperature of the air t', 177 the ratio of the volume of the of mercury vapour referred to air at the saine


connecting tube, &"., to the volume of the bully, a the coefficient tenperature and pressure is known to be 6.92. 10. 1. A porcelain flask with a ball stopper, shown in

Fig. 2.

of expansion of the air, am 233 the coefficient of cubical expansion

of the glass. A similar instrument with a bulbo which will resist tig: 2, No. 2, may be used instead of the iron flask.

Turtine l'apour. Derills and Troost's Pyrometer.—Some of the higher temperatures may be used beyond the softening-pint of lwst-known determinations of very high boiling points have been slus. Pouillet in his classical research on high temperatures? useil

a platinum bulb and comecting tube. He employed the constantmade by Deville and Troost, who cmployed iodine in a manner

pressure method and measured in the manometer tube the variation similar to that in which Regnault employed mercury. Some ioline wits contained in a porcelnin flask of about 300 cc. capacity, with gives instructions for drawing the platinum connecting tube; but no

of volume. Regnault" mentions a platinum air-pyrometer and : tine neek, which just protruded from the source of heat and was results of measurements obtained with it are given. E. Becquerel 9 lovely closed by means of a stopper; when the temperature was machind and the ioline completely volatilized, the stopper was fusel air-thermometer, which rele objected to by Deville and Troost on

published an account of results obtained with a platinum rurvoir to the nozzle by means of an oxy - hydrogen blowpipe. The the ground that platinum beron porous at high tempuratures, 20 of the ioline remaining in the task was determined by weigh- and their objection is supported by an "]riment describeul hy ing, after it haul cooled; the volume of the flask had been pre; them in the legitiir ili Chime plommer, 1-63, . 237, anil viously determinal ; thus the density of the iodine vapour coulil Furthritte der Phusik. 1-03:3, p. 54. Weinholell" und a Jolly's le funt. corre«tion of the volume of the flask was necessary thermometer fitted with a prielain bulb and connecting tube, and in consequence of the expansion of the Bayeux porcelain of which Deville and Troost are of opinion that porcelain forins the only it was composel. This was obtained from independent observa- suitable material for gis-thermometer lullos for prey high tompera tions of the linear clongation of a rol of porcelain for temperatures ture." For us at high temperatures the gas-thermouter shoull up to 1500); their results give a coefficient of cubical expansion of be filled with at a low pressure, that when heated there may 0-0000109 between 0' and the boiling-point of calmium (856"), 11-0000108 between O' and the melting point of silver (1000": from external air. It is quithapis unneessary here to insint upon the

be no meat ditforner of posus-118" lwt Weron the interior and the 01100016 to 0-000017 lwtween 1000 and 1400', reaching '000020 necessity for the completo desiration of the interior of the lub foranks 1500'. The specific gravity of inline rapour was taken to and of the sous emplogvel. Der $716, referred to air at the same temperature and pressure : # The last Wolitiation of the themometrs to whirl it in this zesumption was justified by a ditional observations with air

neressary to attention is that conjuntoil an: 1298 ad lis Parhelo:,' 811• by using the number in a determination of the density of intended for rezulinhigh tempat it're i!ly to an athy of stram at the boiling point of mercury.

within two or thropologies Iirol-ints of a wall. ylimma bul! 3: The Monometric Gas-thermuniter. In the constant pressure tothenis of mrasuring temperature which have just been des ribel Vir" 15., T.

SI!. 7. 1. p. 12. une experiment gires only a single observation of the temperature.

"...rr.....", Corp. ir... Del 1.15.), . 75. Verile", V

... Misi, 131, Txill. n.19.

11 lear! Tron 29.11.reli firbeltoftati • Vaan of results of in Meyer, Damas, Mitxclierlich, anel Rincan. Ile de elimir, (3Iril 27.

1: ... 11,

nil. V... 141.


[ocr errors]
[ocr errors]
[ocr errors]

" ....1. n., .

[ocr errors]

T-0=(0 - 1)

reservoir air-thermo-

reservoir air - thermo-

air - thermo




Mean spec. heat.

spec. heat.

spec. heat.


of glass or silver of 4 cc. capacity connected with a vertical stem of temperature of a furnace. Certain "pyrometrical beads” or “trials”
thermometer tubing of 0.2 mm. diameter. This stem terminates -i.c., small hoops or gallipots of clay-indicated the temperature
in an open vessel of mercury, and thus the pressure of the gas can by their tint much in the same way as the proper temperature is
be measured. Berthelot's instrument is graduated by reference to indicated by the colour of steel in tempering.
four fixed points, namely, the freezing-point and boiling-point of § 6. The Calorimetric Vethod.—This is a very conveni-
water, and the boiling points of mercury and sulphur. In order
that the mercury index may move easily in the tube, extreme care

ent method and is often practically employed for measurmust be taken in drying the tube, and only perfectly pure mercury ing the temperature of furnaces. The observation consists can be used.

in determining the amount of heat given out by a mass $ 4. The results obtained by any of the air-pyrometric of platinum, copper, or wrought-iron on cooling in water methods just described may be employed to express directly from the high temperature. The theory is simple. Let the temperature of the pyrometer in numbers agreeing m be the capacity for heat of the calorimeter and of the closely with the thermodynamic scale. The other instru water contained in it, is the mass of metal, T the temments to which we now turn our attention can only be perature required, t the initial temperature of the water in regarded as intrinsic thermoscopes, which, in order to give the calorimeter, 0 the final temperature of the water after intelligible numerical results, must be graduated by direct the introduction of the metal, and k the mean specific heat comparison with an air-thermometer. Some of them may of the metal between the temperatures @ and T. Then indeed be used by extrapolation to give a numerical measure of temperatures outside the practical range of

JI.K the air-thermometer, employing for that purpose a formula The value of K, the mean specific heat of the metal between the verified for temperatures within the range. A case in temperatures occurring in the experiment, must be determined by point is the determination of the temperature of fusion of precisely similar calorimetric experiments, in which the high templatinum by the calorimetric method described below. perature T is determined by the application of one of the air-pyro

meter inethods. The following table (II.) gives the best-known These intrinsic thermoscopes are frequently much more determinations of the mean specific heat of platinum for different convenient in practice than any of the modifications of ranges of temperature. the air-pyrometer.

Table II. -- Jean Specific Heat of Platinum. $ 5. Discontinuous Intrinsic Thermoscopes.—The best ex

Pouillet, 5) by platinum Weinhold1,6 by porcelain Violle, 7 by porcelain re-
ample of the measurement of temperature by a discontinu-
ous intrinsic thermoscope is that suggested by Prinsep). 1
He formed a series of definite percentage alloys of silver

Range of
Range of

Range of

and gold and of gold and platinum. The melting points

0°- 100' 0.03350

0°-100° 0.0323 of these alloys give a series of fixed temperatures lying between the melting-points of silver and gold and of gold and platinum respectively. An observation is taken by exposing in the furnace, upon a small cupel, a set of small

09-781° 0-0365 flattened specimens of the alloys, not necessarily larger than pin heads, and noticing which of them are fused.

0°-1000® 0-0377 The temperatures of fusion of these alloys have been determined

by Erhard and Shertel"; their results are given in the following
table, taken from Lanlolt and Börnstein's Physikulisch-chemische

Violle's results give, if co be the mean specific heat between

(° anl to, CP=0.0317 + .000006t. Assuming this formula to hold

beyond the verified limits, he obtains by calorimetric observations Table 1. —Thc Fusiny-Points of Prinsop's Illoys.

1779° C. as the temperature of the melting- point of platinum. The true specific heat of wrought-iron at temperature t is accord

ing to Weinhold (1.c.) given by the formula ce=co+at+ ßt”, where Per cent. Fusing

Fusing Co=():105907, a=0.00006538, B=0.000000066477, and the total of gold. point.3

of golel. point. heat obtained from unit-mass of wrought-irou cooling from t, to tio

is therefore S(C, +at+bt2)dlt. The specific heat of copper does not 20

appear to have been accurately determined for high temperatures.

The determinations by Bède, quoted by Landolt and Börnstein 2. GOLD AND PLATINIM.

(op. cit., p. 178) are

159-100mean specific licat 0-09331 ;

of gold.
platinun. point.3
of gold. platinum. point.

There are two obvious sources of error of considerable amount in 5

the use of the calorimeter for pyrometrical purposes, viz., (1) the liability of the metal to lose heat during its passage from the furnace to the calorimeter, and (2) the evaporation of water from the

calorimeter. With the small mass of platinum generally used, 1610'

the former source of error is likely to be very important, for the temperature of a mass of 50 grammes of mercury at 100° C. may fall a full degree in being carried to a calorimeter 3 feet away. It does not appear that any estimates of the amount of loss which may

be so proluced in calorimetric determinations have been published; It is said, however, that some difficulty is met with in the use but in order to reduce the loss Salleron 8 suggests the employment of Prinsep’s alloys in consequence of the property possessed by of a platinum or copper carrier in which to heat the mass of metal, silver of taking up oxygen when melted and ejecting it on solidlify- and J. C. IIoadly," uses a graphite crucible for that purpose. The ing and of molecular changes in the alloys which make it unadvis- second source of loss is more easily disposed of. Weinhold (1.c.) able to use the same specimen more than once. A similar method uses a calorimeter closed by a lid and quite filled with water. This has recently been employeıl by Carnelley and Carleton Williams, is provided with a broad tube passing nearly to the bottom of the in which metallic salts with high fusing-points were employed calorimeter, and the latter is tilted while the platinum mass is instead of alloys, the fusing-points being initially determined by a being introduced; whereas Violle 10 gets over the same difficulty by calorimetric method. Theso methods recall an old empirical method

the use of a calorimeter provided with a platinum “éprouvette, sometimes employed in porcelain manufacture for estimating the so that the heat is imparted more slowly to the water. In a calori

metric pyrometer for technical purposes, made by Messrs Siemens 1 Phil. Trans., 1828, p. 79. 2 Jahrb. für das Berg- und II itten-Ilesen in Sachsen, 1879.

5 C. R., iii. p. 786 (1836). 6 Pogg. Inn., cxlix, 3 Determinations of temperature by a porcelain air-thermometer. 7 Phil. Mag., [5], iv. p. 318. 8 Chem. Neurs, xxvii. 77. Errors in general less than 20°.

? Jour. of Franklin Inst., xciv. P. 252. 4 See Chem. Soc. Jour., 1876, i. 489 ; 1877, i. 365 ; 1878.

10 Phil. Jug., [5], iv. p. 318.

200 300 400° 500° 000? 700' 800° 900' 1000 1100°


| 0.03560


10.2 - 99:1
16 19-238.5
17.) -256.8
23.5 -170°
2.46 -478
20.7 -70.5
23.6 -7000
22:3 -931°
17.3 -952



[ocr errors]


Per cent.

Per cent.
of silver.

Per cent.

of silver.

[ocr errors]
[ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][merged small][ocr errors]
[ocr errors]
[ocr errors]


[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]
[ocr errors]

10 80 90


[ocr errors]




Brothers, the mass of metal employed is a copper cylinder. For strument as supplied by Messrs Siemens Brothers is exceeilingly a sketch and description of the instrument, see Iron, vol. xiii. p. convenient. It is shown in fig. 4. P is the coil of platinum-wire 304 (fig. 21).

wound on a cy$7. Continuous Intrinsic Thermoscopes. The other pyro

linder of fireclay,

and connected by metric methods to which we have space to refer are those

stout platinum which depend on the continuous variation of some property wires X, Ü, C of a body with variation of temperature. Each instru- with three bindment of this kind requires graduation by direct or indirect ing screws at the

end of a stout comparison with an air-thermometer. The methods may

iron tube 6 feet be grouped under three heads,—(1) the expansion of a rod long, and thereby of metal or earthenware; (2) the variation of electrical with an arrangeresistance of a wire ; (3) the electromotive force of a thermo- ment for comparelectric junction.

ing its resistance

with that of a (1) Expansion of Jctals and Earthenware. — The necessity for the standard coil x, measurement of high temperatures has been most felt perhaps in by means of difpottery manufacture, and in consequence many attempts have been ferential voltamade by potters to establish a system of pyrometry based ou the meters 1, V. A permanent contraction which clay undergoes when exposed to a current from six high temperature. The action of Wodgwood's pyrometer described Leclanché cells in the Phil. Trans., 1782, 1784, and 1786, (lepends on this property is divided into

4MH of clay. The linear contraction of a clay cylinder was measured two parts, one by means of a metal groove with plane sities inclined to each other going through at a small angle, and the temperature was estimated numerically the standard coil loy comparing the contraction with that proluced by a known dif- Y, the voltaference of temperature

. The results were not very satisfactory; meter 1", and an since the clay would contract the same amount by long-continued additional plaheating at a lower temperature as by a short exposure to a higher tinum wire, also our. Welywood's estimate of the melting point of cast iron was marked 1, join20,577 Fahr.

ing the other The measurement of temperature by the expansion of a metal branch again at rol has been very froquently attempted. The first instrument to the end of the which the name of "Pyrometer" was given was of this kind, and platinum coil, was durised by Muschunbroek, and others were devised in the carly while the other part of the century by Des Águliers, Ellicot, Graham, Smeaton, branch includes Forynson, Broyniart, Laplace, and Lavoisier, and later by l'ouillet. the voltameter We may say here that the only acccurate methods of measuring the 1, the connectextremely minnte elongations of metal roils are those in which the ing wire i, and expansion is referred by some optical arrangement to a scale kept the coil P. Tho quite uninfluenced by the source of heat which causes the expansion. wire l' is comIn this respect Pouillet's method of employing the expansion of a mon to both cir

Fiy. 1. ml is superior to those previously employed.

cuits. The amount of gas generated in the voltameters is inversely The relative expansion of a metal in an earthenware socket was proportional to the resistances of the respective branch circuits. ciuployeel by Daniell in his well-known pyrometer. The relative | Thus, if I' and 1” be the volumes of gas in the two roltameters

spansion was indicated by an inlex of porcelain which was pushed respectively, forward when the bar expanded and left behind when it contracted,

I' Resistance of l' and its connexions RI) that after the apparatus had cooled the expansion could be measured at leisure by the scale provided : Que allowance was made

"Resistance of land its connexions for the expansion of the index itself. Quite recently the expansion The dealing wires from the screws of the iron tube to the como graphite has been employed for pyrometry loy Steinle and mutator Bll'are bound together in one cuile, so that they have the llarting' As the result of his experience, however, Weinhold same resistance: thus the observal variation in the ratio of the states that it is not possible to obtain trustworthy measurements resistances may be regarded as entirely due to the variation in the of temperature from an instrumeut depending on the relative expan- resistance of i. The height of the liquia in the two voltameters sion of solid boilies

can be adjusted by the short glass tubies S, Solidling vertically on An ingenious application of the relative expansion of gold, silver, the Woodlin support to which the voltamters are attachel

. They anl platinum was introluceol by Breguet. 'Very narrow strips of are connected by means of in.lia-rubber tubing with the voltametors. the three metals are fastened together to form a compound ribbon The commutator BB' is used to reverse the lirution of the current spiral, and to the end of the spiral is attached a neville, which, as Flery till seeones cluring the oloration, which lasis long nough the comperature changes, moves over a ytauluate cirele. The in to give a sutli iunt -111ply of hon in the voltameter tubes By strument, of course', requires empirical gravluation. A molitiration this artifice the llor clue to wariation in the polarization of the of it is sometimes used to mea-ure the temperature of the hot blast octrodes is avoided. of an iron furnace.

The voltantrie arrangement for comparing the tesites lolitriation of Electrial Rusistane, - pyrometric method simplities Vrly greatly the app-21 10119 required. In a laboratory tlu. fivunill on the ririation of the electrical resistance of a platinum 1esistances m.iy bu, of cour, m. 19 d'ately complead by means of wire he len practically carried out by Siemens, and was des resistante pocoils and a galvanople.for. For tuhnid pipes the erived for him in the Bakerian lecturi Pres. Roy. Soc., 1871! toin palaturin up to 1100 l Dolunmal from the clown Various les mans "..«umin; dynamical law, according to which the electrical 20 of a very continut siile meFor 1-11111:111.- Prodil 1400 sistan'e inenax's accorling to the relocity with which the atoms the sale ulation has !" !" !through. Thusyuritdial 1177 ar mured by heat, a paralolie ratio of inirease of resistance with on which the viction of the formuluoti netermination of in raw of temperature follows, anl in adding to this the coelli- the constants list are not very mum 10119. B-jelentleme.1-111 111euts cient. Popresenting lin·ar expansion and an ultimate minimum of Suments referred tobon, there is a primental comicon pislin in the resistance r for any temperature is expresseul lip the lix Weinboliloftla lrslit obtained on this in minunilor general formula r=17+7+ which is found to agree very of an air-thermometer. For the serijos 1!, O of clowly lth with the experimental data at low temperatures suip the coil in roolil. The toniki: liptom), udiniliw p'i'l hy Dr Jatthirschen and with the experimental risults varying at the 19.111 of to listov ille! 11.:lol... I ...:•:13 w;" to 1900' C." The details of the expurimental verification at wishin!: the lone w 100... -in. 11 nie giron in the abstract of the lectur. nor are the numri i tion af ili of six to 111.1111ges, this of il. - 1.01331 ..! ralar of the constants for platinum. But Wrinhold res the 533 and the loan !!"l'll not infummation, obtained by letter from the lecturer, that I is the +20 at the lovrimit at the 13ti. T!, art! :) a'mulate trmperatun', and the numerical values of the constants for comparing the painfalls to folitul zin w widos nivel . 00:33369, 3=0.00218107, 7 = -021127.

suiliinily writive. Sinds on this incrime 1: Wall The reporiinental arrangiment for practical purposes of the in mitted perry purimerit list 0.1111itor at the Briti! 11:31

17.07", 1971, their uit non 10.10gosilor. po waliit!) See Beckert, Zeitschr. f. anil. Chem., XXL p. 248, 1952. of the 4te-1101 whether tlor printimitetlar !... !--:. Ingy. Inn., cxlix. p. 206.

an e' attir lein Tropa bills locis Loncil. It would that

« EelmineJätka »