LIBRARY 
 
 OF THE 
 
 UNIVERSITY OF CALIFORNIA. 
 
 Class 
 

 LABORATORY NOTES 
 
 ON 
 
 HEAT MEASUREMENTS 
 
 BY 
 
 CHARLES L. NORTON 
 
 COPYRIGHT, 1902, BY CHARLES L, NORTON 
 
 PRINTED BY THE SOUTHGATE PRESS 
 T. W. RIPLEYCO., BOSTON, U.S. A, 
 
LABORATORY NOTES 
 
 ON 
 
 HEAT MEASUREMENTS 
 
 BY 
 
 CHARLES L. NORTON 
 
 OF THE 
 
 UNIVERSITY 
 
 OF 
 
 COPYRIGHT, 1902, BY CHARLES L. NORTON 
 
 PRINTED BY THE SOUTHGATE PRESS 
 T. W. RIPLEYCO., BOSTON, U.S.A. 
 
LABORATORY OF HEAT MEASUREMENTS 
 
 The instruction in heat measurement consists of a series of 
 lectures and laboratory exercises which have for their object 
 the training of the student in such methods of heat and 
 temperature measurement as will be of value in later scien- 
 tific or technical work, and to furnish a foundation for 
 research in thermal lines. Perhaps no portion of the heat 
 measurement field is so fruitful, both to the scientific and to the 
 technical investigator, as is the measurement of high tem- 
 peratures, or pyrometry. Next in importance comes the 
 measurement of the efficiency of fuels, the determination of 
 their calorific power. To these two subjects the first portion 
 of these laboratory notes is devoted, with the expectation 
 that the additional notes on " thermometry," " thermal con- 
 ductivity," and "electric-heating apparatus and methods" 
 may soon be added. 
 
 All reports handed in must be taken upon the proper 
 blanks and Tegular physical laboratory paper and should be 
 accompanied by the original records. All reports must be 
 sent in within two weeks of the time the observations were 
 finished. When sent back for correction they should be 
 returned with all necessary corrections within one week. If 
 not returned to the student within two weeks from their first 
 presentation, the experiments may be assumed to need no 
 correction, and they will not be returned to the student until 
 the end of the term. 
 
THE LE CHATELIER THERMO-ELECTRIC PYROMETER 
 
 The Le Chatelier thermo-electric pyrometer is based upon 
 the increasing electromotive force which exists at a junction 
 of two metals as the temperature rises. If we have a pair 
 of dissimilar metallic wires, their junction becomes the seat 
 of an electromotive force, and if they be joined at both 
 ends, a current will flow through them as the result of the 
 difference between the electromotive forces at the two ends 
 of the wires. In general, this current is dependent upon the 
 difference in temperature, though not directly proportional 
 to it. In order to use this phenomena as a basis for a 
 pyrometer, since there is no known relation existing directly 
 between temperature and electromotive force in such a cir- 
 cuit, we must expose the junction to known temperatures 
 and note the current flowing, and in this way calibrate. It 
 is usually customary to observe, not the electromotive force, 
 but the current, keeping the total resistance of the circuit 
 constant in order that this may be allowable. 
 
 This pyrometer is by far the most important instrument 
 for the measurement of temperature from the point of view 
 of the engineer. It may be found described in detail in 
 Le Chatelier's " High Temperature Measurements," pages 
 92 to 128 (Burgess translation). 
 
 The apparatus consists : first, of a pair of platinum and 
 platinum-iridium wires; second, of a galvanometer; ana 
 third, a pair of suitable connecting leads. 
 
 Leads. The lead wires connecting the galvanometer to 
 the junction do not require any special care, other than that 
 necessary to keep them well insulated. These wires should 
 be of seme good electric line-wire, not smaller than No. 14, 
 and they should preferably be of the so-called " rubber-cov- 
 ered " type. 
 
LABORATORY OF HEAT MEASUREMENTS 
 
 Junction. The junction to be used is composed of one 
 wire of platinum, and one of platinum with ten per cent, of 
 rhodium or iridium. This couple costs nearly ten dollars a 
 foot and must be used with great care. The wires are some- 
 what brittle, and they are easily attacked when hot by many 
 of the baser metals. The junction in its simplest form is 
 made by merely twisting the wires together at one end and 
 then twisting each to the leads at the other end. It is desir- 
 able, however, to be able to know the temperature of the 
 junction of the couple with the copper leads, and it is there- 
 fore best to inclose the joints in some receptacle in which a 
 thermometer bulb can be inserted. For laboratory work, a 
 
 FIG. I . Diagram of Thermal Couple. 
 
 small bottle with a stopper perforated for the leads and ther- 
 mometer serves to keep the junction at a fairly even temper- 
 ature. Where greater constancy of temperature is needed 
 the bottle may be wrapped with some insulating material, 
 felt, magnesia, or asbestos. It is sometimes necessary to 
 put the "cold junction," as the copper-platinum end of the 
 couple is called, in a large block of iron to insure its chang- 
 ing temperature only at a very gradual rate. 
 
 The couple must be insulated from itself and from sur- 
 rounding conductors throughout its length. The best insula- 
 tion for the cool portions of the wires is a firre rubber tube, 
 while the hotter portions may be insulated with asbestos 
 string wound over and under, in figure-eight fashion, or they 
 may be protected by means of small clay stems with a 
 double bore. 
 
THERMO-ELECTRIC PYROMETER 5 
 
 To insure a constant resistance of the couple and leads it 
 is, in all cases, best to solder the cold junction with ordinary 
 soft solder. Resin, and not acid, should be used in fluxing 
 this joint, or a slight electromotive force will be found 
 to result, giving serious disturbance to the galvanometer 
 readings. 
 
 Unless there is a switch on the galvanometer there 
 should be one inserted in the circuit, as it is necessary to 
 open the circuit frequently for the purpose of reading the 
 zero. 
 
 Galvanometers. There are many galvanometers suitable 
 for use with a thermal couple. Directions will be given for 
 the adjustment and operation of those now in use in the 
 Laboratory of Heat Measurements, and since the galva- 
 nometers are of the same general class it is probable that no 
 great difficulty will be found in applying them to others. 
 All the galvanometers especially suited for this work are of 
 the D'Arsonyal type, of medium sensitiveness. They oper- 
 ate by the change in position of a coil of wire in a magnetic 
 field, as the current in the coil changes in strength. This 
 change in position is noted either by observing the move- 
 ment of a pointer attached directly to the coil, or by noting 
 the excursion of a beam of light falling upon a small mirror 
 attached to the movable coil. Galvanometers which may be 
 read by a pointer are made by Heraeus, and Hartmann and 
 Braun. The galvanometers of Sullivan and Carpentier are 
 the best of the instruments using a mirror and scale. The 
 more important details of the procedure in setting up each of 
 these instruments are given below. 
 
 Carpentier galvanometer. This instrument is that most 
 commonly adopted for pyrometric determinations. It will 
 be found described in Le Chatelier, pages 108 to no. To set 
 up the galvanometer one should select a place as free from 
 vibration as possible, and screen it from any but a feeble 
 light. - The galvanometer box should be firmly attached to 
 the wall, taking care to see that it is plumb. The small bob 
 inside the box is intended to assist this operation. Next 
 slip the coil over the iron block between the pole pieces, with 
 
6 LABORATORY OF HEAT MEASUREMENTS 
 
 its mirror facing in the direction in which the lamp and scale 
 is to be placed. The suspensions consist of short pieces of 
 fine German silver wire with little balls of the same metal 
 wedged on to the ends. The lower end of the upper sus- 
 pension should first be inserted in its eye at the top of the 
 coil. See that it is slipped well back in the slot. Next 
 hook the upper end of the suspension in the eye in the flat 
 spring near the top of the box. If the suspension is appar- 
 ently too short loosen the tension of the flat spring by means 
 of the thumb-screw. Next drop the lower suspension into 
 
 FIG. 2. Carpentier Galvanometer. 
 
 place in the opening between the magnets, and put its two 
 ends in the eyes as before. The mirror may now be made 
 to face in any desired direction by taking the ball at the 
 lower end of the lower suspension between the thumb and 
 finger and twisting it slightly. This is the most troublesome 
 operation of the whole process, and must, moreover, be 
 accompanied with the exercise of great care and patience, 
 or the only result of a great expenditure of time will be a 
 pair of broken suspensions. A small amount of adjustment 
 of the light spot may be gotten later by means of the screw- 
 feet at the bottom of the box. 
 
 The lamp and scale should next be set up at a distance of 
 about a meter. It is well to light the lamp and move it back 
 
THERMO-ELECTRIC PYROMETER / 
 
 and forth, and up and down, until it is found that the image 
 is well focussed, and at such a height as makes both the 
 divisions and numbers of the scale visible. When its proper 
 position is found the base-board should be firmly fastened to 
 the wall. It is well to put in a strong screw at the middle of 
 the board near the bottom, in addition to the screw r at the 
 top. The oil lamp which is often used where the apparatus 
 is to be carried about, often covers the lens with dew for a 
 few minutes after lighting, and it is well to put off any 
 attempts at focussing until this has disappeared, after the 
 whole lantern becomes warm. As this lamp requires refilling 
 at very short intervals, it should be used only when absolutely 
 necessary. Either a small gas burner or an incandescent 
 lamp .should be used whenever possible. 
 
 Heraeus galvanometer. This galvanometer reads by 
 means of a pointer attached directly to the coil. The coil 
 must therefore move through a much larger angle than in 
 the case of the.Carpentier instrument with its long beam of 
 light. To make the galvanometer sufficiently sensitive to 
 accomplish this, it has been necessary to use a very fine 
 suspension wire, and to use only the upper suspension. The 
 galvanometer is therefore more frail and must be handled 
 with great care. There are only two adjustments neces- 
 sary : first, level by means of the screw-feet and the circular 
 level attached to the base ; and second, loosen the brass 
 thumb-screw which projects through the side of the brass 
 case. This removes the supporting spring which lifts the 
 coil and takes all strain from the suspension. It is abso- 
 lutely necessary to screw this thumb-screw firmly in, before 
 attempting to move the galvanometer, otherwise the suspen- 
 sion is quite certain to be broken. There are two scales 
 upon the dial. The outer scale is intended to read in Centi- 
 grade degrees directly, with an upper limit of 1600. The 
 lower scale is in millivolts and it is intended to make the 
 instrument thereby available as a voltmeter as well as a 
 pyrometer. In several of the later galvanometers of this 
 kind there is noticeable considerable " pivot friction," mak- 
 ing it necessary to tap the glass of the galvanometer contin- 
 
8 LABORATORY OF HEAT MEASUREMENTS 
 
 ually to be sure of freedom from error due to the pivo* 
 sticking. None of the joints in these galvanometers in the 
 laboratory were soldered when they were purchased, and 
 their variations in resistance made it necessary to solde* 
 most of them. 
 
 Sullivan galvanometer* This galvanometer is similar in 
 many respects to that of Carpentier. It reads by means ot 
 a mirror and has an upper and lower suspension. It is. 
 however, more sensitive and it is so free from disturbance 
 from jarring that it may be satisfactorily used on an ordinary- 
 laboratory table. Further, the suspension is stout enough to 
 allow the galvanometer to be readily handled and shipped 
 without any unusual care. As set up in the laboratory, it is 
 to be used with a telescope and scale. The scale must first be 
 set up in front of the galvanometer at a distance of about a 
 meter. The telescope should be focussed on the plane mir- 
 ror and then gradually refocussed until the image of the 
 number on the scale can be clearly seen. Some care is 
 needed in placing the scale and telescope at the proper 
 height, and also in a plane perpendicular to the axis on 
 which the coil turns, so that the image may remain in the 
 field of view as the mirror turns. Care must be used not to 
 disturb the focus of the telescope after calibrating, as the 
 axis of the telescope is not sufficiently constant in position to 
 allow of even slight adjustments, without altering the appar- 
 ent position of the cross hairs. 
 
 Calibration. Having prepared the junction and having 
 gotten the galvanometer set up and attached to the leads 
 through the switch, the galvanometer may now be cali- 
 brated. To do this we observe the deflection of the gal- 
 vanometer which corresponds to a known difference of 
 temperature at the two ends of the thermal junction. The 
 most convenient temperatures to use are the boiling and 
 melting points given below. The cold junction may be 
 placed in a steam or ice bath, when desired, but it is usually 
 sufficient to allow it to remain at the temperature of the 
 room and read its thermometer at intervals of two to five 
 minutes. 
 
THERMO-ELECTRIC PYROMETER 9 
 
 TEMPERATURES FOR CALIBRATION 
 
 Substance. Boiling Point. Freezing Point. 
 
 Water ioo. C. o. C. 
 
 Naphthaline 218. 
 
 Sulphur 444. 
 
 Aluminum 657. 
 
 Copper 1084. 
 
 Gold 1063. 
 
 Platinum 1760. 
 
 The hot junction should be exposed to these several known 
 temperatures while the deflection of the galvanometer and 
 the temperature of the cold junction are noted, in each 
 instance. A plot should then be made having the deflections 
 as ordinates and the difference between the temperature of 
 the hot and the cold ends of the couple as abscissas. If the 
 Heraeus galvanometer is to be used with a couple of compo- 
 sition similar to that for which it was originally graduated, 
 it may be well to make the plot as a plot of corrections, hav- 
 ing readings of the instrument as abscissas and corrections as 
 ordinates. 
 
 To obtain the galvanometer readings corresponding to the 
 boiling points of water, napthaline and sulphur, it is best to 
 put the junction directly into a small test tube of the boiling 
 liquid. It makes no difference whether the junction be just 
 above the liquid or well below the surface. Take care not 
 to heat so vigorously as to superheat, or to cause the vapors 
 to catch fire at the mouth of the tube. The highest steady 
 deflection is, of course, the one to be recorded. 
 
 To find the deflection corresponding to the freezing points 
 of the metals, we may use either a small bit of the metal 
 wrapped about the hot junction or a larger mass in a crucible. 
 To heat the smaller mass, it is only necessary to use a Bunsen 
 burner for the baser metals and an oxyhydrogen blow-pipe 
 for the platinum. For the larger masses, a crucible furnace, 
 similar to the small Fletcher furnaces in the laboratory, will 
 be needed. The metal should in all cases be heated slowly, 
 and the greatest care should be used to prevent heating more 
 
10 LABORATORY OF HEAT MEASUREMENTS 
 
 than a very few degrees above the melting point, as otherwise 
 the platinum and platinum-rhodium will alloy with the melted 
 metal, changing its composition and its freezing point, and 
 the loss of a portion of the junction is also very probable. 
 Especial care is needed when working with hot copper, as 
 the fumes or vapor arising from the melted metal, if it be 
 heated much above its melting point, cause the platinum to 
 be alloyed at a distance of an inch or two from the surface 
 of the hot copper. Since it is difficult to tell from its physi- 
 cal condition, even when large masses are used, at just 
 what temperature a metal melts or freezes, it is best to 
 use the point at which the latent heat of freezing develops 
 as the freezing point. To do this it is only necessary to 
 note the point at which the galvanometer pauses in its 
 swing as the melted metal cools. This momentary pause 
 occurs when the latent heat of freezing develops and pre- 
 vents for a brief interval the temperature of the mass from 
 passing below the freezing point until all the metal has 
 frozen. To find the platinum point it is best to use a long 
 flame from an oxyhydrogen blow-pipe and draw the junction 
 slowly down through it until the platinum wire melts. With 
 care, a drop of melted platinum may be kept on the tip of 
 the wire for several seconds, and the deflection can be read 
 with a precision quite as good as in the case of the other 
 metals. The eyes must be protected from the intensely 
 bright light of the melted metal by very dark glasses, such 
 as are used in examination of the electric arc. The junction 
 wires may be protected from alloying with metals of low 
 melting points by a fine hard glass tube, but in case this is 
 done, larger masses of metal must be used to insure the 
 junction being at the temperature of the melted metal. 
 
 Reports. Each pair of students will be expected to set 
 up their galvanometer and calibrate it, possibly omitting the 
 platinum point from motives of economy. They will next 
 measure several unknown temperatures, preferably the recal- 
 escence points of two pieces of steel, and the melting points 
 of several alloys. In case antimony is used it is necessary 
 to perform the melting point determination under the hood. 
 
PLATINUM RESISTANCE PYROMETER II 
 
 After having gotten the deflections corresponding to the points 
 sought, they should be looked up in the calibration plot, not 
 forgetting the necessary addition of the cold junction tem- 
 perature. Bear in mind that the deflection is dependent 
 upon, not the temperature of the hot junction, but the differ- 
 ence in temperature between the hot and cold ends. 
 
 PLATINUM RESISTANCE PYROMETER 
 
 The platinum resistance pyrometer, or thermometer, of 
 Siemens and Callendar may be found described in Le Chat- 
 elier, pages 83 to 91. It is not always given place among 
 the pyrometers, nowadays, because of the great difficulty of 
 keeping the apparatus in proper condition if used at tem- 
 peratures much above 500 C. Since, however, its preci- 
 sion is very great at low temperatures, and, further, since 
 in the hands of some exceptional observers it has yielded 
 excellent results, it should be classed as one of the most 
 important thermometers. 
 
 The operation of the pyrometer is based upon the increase 
 of the electrical resistance of a platinum wire as its tempera- 
 ture rises. After calibration we have only to measure the 
 resistance of the wire in order to determine its temperature. 
 It will be apparent at once that the method is available for 
 use at great distance and under varying conditions of pres- 
 sure, and in many ways offers advantages over most other 
 methods. Since it is not difficult to measure the resistance of 
 such a coil as may easily be used in this work with a pre- 
 cision of one-twentieth of one per cent., the method takes 
 first place in the ranks of the thermometers in the matter of 
 precision. 
 
 The essential parts of the apparatus are, of course, a coil of 
 platinum wire and a bridge with which to measure its resis- 
 tance. Since the adjustment and subsequent care of a gal- 
 vanometer and Wheatstone's bridge of the greatest precision 
 would be so great as to call for a considerable outlay of time, 
 it is deemed best to use a less sensitive measuring device 
 and devote more time to studying the method of using and 
 
12 LABORATORY OF HEAT MEASUREMENTS 
 
 calibrating the pyrometer. Students will therefore use either 
 the portable testing set or a similar simple bridge with a 
 D'Arsonval galvanometer. The greatest precision sought 
 is a single degree. Be sure and note the number of the coil 
 used. 
 
 Connect up the apparatus and measure the resistance of 
 the coil at the room temperature. The blind leads may 
 either be connected in the opposite side of the bridge circuit, 
 or they may be measured separately and subtracted. Of 
 course the object of this is to enable us to measure the 
 resistance of the coil alone without the leads, and it is for 
 that purpose that the blind leads are inserted. They are 
 of the same wire and length as the true leads, and their 
 position beside the true leads assures their being at the same 
 temperature. Find the resistance of the coil in ice, in steam, 
 in boiling sulphur, and in boiling napthaline. Take great 
 care to keep the tube which protects the coil from too sud- 
 den changes in temperature, as its breaking may cause the 
 .breaking of the platinum coil, a rather serious matter, as 
 these coils are difficult to wind. Having found the resis- 
 tances, compute first the "platinum temperature" -pi for 
 boiling sulphur. This temperature will be found to be some 
 ten or twenty degrees below the true boiling point as ex- 
 pressed in degrees centigrade (444). The formula for this 
 deduction is 
 
 7P /? 
 
 IOQ f ~ -j-pt (in platinum degrees). 
 
 ^100 J?o 
 
 To reduce the pt in platinum degrees to degrees centigrade 
 we must make use of Callendar's second formula, in which / 
 is the temperature in degrees centigrade and pt the platinum 
 temperature as found under the assumption of the equation 
 above, that the increase of resistance is directly proportional 
 to the temperature increase. 
 
 In this equation we may substitute the values of pt and / for 
 the sulphur point and solve for D. This need not be rede- 
 
CALORIMETRIC PYROMETER 1 3 
 
 termined so long as the coil remains free from injury or 
 contamination chemically. Next, with the aid of the first 
 formula, find the platinum temperature of the boiling naph- 
 thaline, and then substitute in the second formula, and find 
 the boiling-point in centigrade degrees. The values of / are 
 of course not known in the substitution in the second formula 
 and -pt may be substituted instead for a first approximation. 
 A second substitution should then be made with the values 
 thus found. This second approximation will be sufficiently 
 precise. Take care to leave the apparatus in the condition 
 in which it was found, especially taking care to cut off all 
 the gas and electrical supply from the boiling-point cans. 
 
 CALORIMETRIC PYROMETER 
 
 The calorimetric pyrometer, or, as it is often called, the 
 specific heat pyrometer, of Siemens and Violle may be found 
 described on pages 74 to 82 of Le Chatelier. The measure- 
 ment of a temperature by the calorimetric method involves 
 the measurement of the heat given out by the pyrometric 
 substance in cooling from the unknown temperature to the 
 temperature of the calorimeter in which it is plunged. If we 
 know the specific heat and weight of the substance, we may 
 compute the temperature, from the total heat received by 
 the calorimeter. Unfortunately the specific heat of such 
 substances as are available for pyrometry varies rapidly with 
 the temperature. 
 
 Let W= weight of the substance (platinum or nickel ball). 
 w = weight of water in the calorimeter. 
 5 = the specific heat of the calorimeter and stirrer. 
 t = initial temperature of the calorimeter. 
 / 2 = final temperature of the calorimeter. 
 T == ; unknown temperature to be measured. 
 s r = mean specific heat of pyrometric substance (o to 
 s t = specific heat of pyrometric substance (o to / 2 ). 
 c = weight of the calorimeter and stirrer. 
 
14 LABORATORY OF HEAT MEASUREMENTS 
 
 Then when the substance is taken from the furnace, and is 
 plunged into the calorimeter whose temperature thereupon 
 rises from t, to t 2 the transfer of heat is shown by the fol- 
 lowing equation : 
 
 WTs T - Ws,i, = (t, _ /,) (TV + cs) 
 and 7W^><T + -W 
 
 All the terms in the right-hand member of this equation 
 are known after the transfer and subsequent rise of temper- 
 ature. The term at the left Ts T is the total heat given out 
 by one gram of the substance in cooling from T to o. 
 This quantity has been very carefully determined for platinum 
 and nickel by Violle and others. The values for platinum are 
 given in the table below, for temperatures over a wide range. 
 
 T Ts T 
 
 100 .......... 3.23 cal. 
 
 200 .......... 6.58 
 
 300 .......... 9-75 
 
 400 .. ........ 13.64 
 
 5 ........ - J 7-35 
 
 600 .......... 21. 18 
 
 700 .......... 25.13 
 
 800 ...... .... 29.20 
 
 9o ......... 33-39 
 
 1000 .......... 37.70 
 
 noo .......... 4 2 - I 3 
 
 1200 .......... 46.65 
 
 14 .......... 5 6 - J 4 
 
 1500 .......... 61.05 
 
 1600 .......... 66.08 
 
 1700 ..... ..... 71.23 
 
 1800 .......... 76.50 
 
 Having computed the value of the left-hand member of the 
 equation by substituting the numerical values, the value of T 
 
CALORIMETRIC PYROMETER 1 5 
 
 may be found by interpolating between the values of Ts T in 
 the tables. 
 
 Apparatus for temperature measurement in this way is of 
 all degrees of refinement, from an old tin can and a bit of 
 firebrick and an ordinary house thermometer, to the care 
 fully jacketed calorimeter for use with the platinum ball in 
 the laboratory. There is no other method which can be used 
 
 FIG. 3. Calorimetric Pyrometer. 
 
 with so little initial cost, nor so available in regions where 
 little apparatus is to be had. The precautions to be observed 
 are the following : If iron is used for the ball it must be 
 weighed each time, as the scale which forms is of consid- 
 erable weight. It is not best to use iron for any but rough 
 work. The water in the calorimeter should be of such 
 amount as to give a rise of temperature of about five degrees, 
 as the calorimeter thermometers are to be read to -rW The 
 water at the start should be five or six degrees below the tem- 
 perature of the room. Vigorous stirring is necessary. The 
 
l6 LABORATORY OF HEAT MEASUREMENTS 
 
 tongs with which the ball is taken from the furnace should 
 be heated to a temperature as near as possible that of the 
 ball, so that the ball may not be unnecessarily cooled on 
 being grasped. Use all possible speed in making the transfer 
 to the calorimeter, as the ball cools very rapidly by radi- 
 ation in even a very few seconds. A i5o-gram ball of nickel 
 or platinum should be allowed to remain in the furnace at 
 least twenty minutes before attempting to use it to measure 
 the temperature, as it is slow in arriving at the exact tem- 
 perature of the furnace. 
 
 Each student will make a measurement with this instru- 
 ment of the temperature of melting sodium chloride, and 
 such other points as the instructor may call for. The 
 nickel and platinum balls or cylinders are to be returned to 
 the instructor after using. Great care must be taken to 
 avoid contact of the platinum with hot firebrick or other 
 material which would alter its chemical purity. The ball 
 must always be heated on a small platinum tripod or a little 
 pan made of stout platinum foil. In order that the ball may 
 not be further contaminated by alloying with the metal of 
 the calorimeter, a net of platinum wire is suspended in the 
 water of the calorimeter. Failure to properly care for the 
 platinum ball when in use may lead to a very consider- 
 able and wholly unnecessary expense. The calorimeter is 
 mounted on wheels, to permit of its being drawn very near 
 the furnace and quickly removed, so that the transfer of 
 the ball may be made rapidly, and yet the calorimeter need 
 be exposed to radiation from the furnace for only a short 
 time. 
 
 To measure temperatures of about one thousand degrees 
 with a platinum ball weighing one hundred and twenty-five 
 grams, we need, if we wish to have a temperature rise of five 
 degrees, 500 to 900 grams of water as deduced below. 
 125 x 37-7 = 5 x W, 
 W 940 grams approx. 
 
 This, of course, makes no allowance for the weight of the 
 calorimeter, and this need not usually be considered in 
 
LE CHATELIER PHOTOMETRIC PYROMETER Ij 
 
 estimating the amount of water needed. We may then use 
 from five to nine hundred grams of water, and get a rise in 
 temperature of from five to ten degrees. 
 
 The only advantage of using distilled water for this work 
 is that it is possible to keep the calorimeters and thermom- 
 eters much cleaner when it is used. The apparatus is to be 
 left in the condition in which it was found, with the current 
 for the motor cut off. The thermometers are to be returned 
 to their rack, and, as was earlier noted, the platinum ball is 
 to be returned to the instructor. 
 
 LE CHATELIER PHOTOMETRIC PYROMETER 
 
 This instrument may be found described in detail in 
 Le Chatelier, pages 144 to 148. It is a portable photometer 
 for the measurement of the intensity of the red light given 
 out by a hot body. When a body is heated it becomes first a 
 dull red, and then a brighter red, then yellow, and finally 
 white. The eye does not indicate that as the temperature 
 rises the intensity of the red increases, because the increase 
 of other colors is greater, but it has been found that the 
 increase of the intensity of the red radiations bears a certain 
 definite relation to the temperature increase. Red is selected 
 because it is present in measurable quantities at lower tem- 
 peratures. For high temperatures it would be quite possible 
 to use yellow or blue light. By this method, then, we are to 
 measure the temperature by measuring the intensity of the 
 red light given out by the body whose temperature we are 
 seeking. The nature of the surface of the body determines 
 to a considerable extent the amount of light which will be 
 radiated from it when it is raised to a certain temperature, 
 but as this instrument is essentially a secondary one, which 
 must of necessity be calibrated, it is only necessary to cali- 
 brate it upon some surface which may be later used as the 
 surface whose brilliancy is measured and under the same con- 
 ditions as prevail in its later use. A small piece of platinum, 
 or a bit of refractory clay will answer for this purpose. 
 
 The photometer itself is of the Cornu type, and it is shown 
 
i8 
 
 LABORATORY OF HEAT MEASUREMENTS 
 
 in plan and perspective in the accompanying cuts. There 
 are two telescopes so arranged that we may see on looking 
 into the common eyepiece, as if side by side, the standard 
 lamp and the object whose temperature is sought. Then 
 by means of the diaphragm in the direct telescope we grad- 
 ually diminish the apparent brilliancy of the object until 
 it just matches in intensity the standard lamp. The amount 
 of '< stopping down " necessary to make the two images 
 match in brilliancy is dependent upon, and a measure of, the 
 temperature of the hot body. In other words, the hotter the 
 
 FJG. 4. Le Chatelier Photometric Pyrometer. 
 
 body, the more we must close the diaphragm in order to 
 make the two images appear of the same intensity. 
 
 The instrument as shown in perspective in figure 4 and in 
 plan in figure 5 consists of the telescope 71 with the eye- 
 piece E, the bent telescope T z with the mirror M so placed 
 as to bring its objective in line with the eyepiece E; the 
 standard lamp S, and the * * cat's-eye " C. The arm W 
 carries a counterweight to make the apparatus more stable. 
 Usually the standard lamp used for this instrument is a small 
 kerosene lamp. This is a source of great inconvenience, and 
 moreover its variations in brilliancy are considerable. It 
 should be replaced whenever possible by an Argand burner 
 or a large kerosene lamp, having a flame not less than 30 
 
LE CHATELIER PHOTOMETRIC PYROMETER Ip 
 
 millimeters in height or breadth. This will give a standard 
 which should be constant in intensity within about two per 
 cent. The mirror M which deflects the beam of light from 
 the lamp into the eyepiece is of black glass with an exceed- 
 ingly keen edge, so that the two images may appear to be 
 in close contact with no dark line between. If the mirror 
 should become displaced, so that a dark line appears between 
 the images, the instructor should be called upon to readjust 
 it. The eyepiece E needs no adjustment nor any special 
 mention, except that it is liable to become coated with dust 
 
 FIG. 5. Section of Photometer. 
 
 and will need frequent cleaning. This applies as well to the 
 objectives. The cat's-eye C has a scale attached which 
 indicates the amount of the travel of the diaphragm in clos- 
 ing or opening. It should be in such adjustment as to read 
 zero when the cat's-eye is closed. The telescope T 2 needs 
 no focussing but T r must be carefully focussed upon the 
 object under examination. This is accomplished by sliding 
 the telescope tube in or out after loosening the small set 
 screw on the top. Since there is some uncertainty as to 
 effect -upon the intensity, as measured by this particular 
 instrument, of light coming from bodies at different distances, 
 it is best to calibrate the instrument at the same distance as 
 that at which it is to be used. 
 
2O LABORATORY OF HEAT MEASUREMENTS 
 
 One or two meters may be selected as a convenient distance 
 for the laboratory. 
 
 Having gotten the instrument together, and pointed it at 
 the small furnace which is to be used to heat the calibrating 
 surface, the standard lamp should be lighted and the tele- 
 scope focussed. This can be best done when the cat's-eye 
 is wide open. If the furnace is not yet red hot, a match flame 
 may be held near the furnace to focus upon. It is well to 
 let the lamp burn for some minutes before beginning the 
 observations, in order that the lamp may become heated and 
 burn at its normal brilliancy. The telescope should next be 
 directed toward the piece of platinum in the furnace which is 
 to be used to calibrate with. This platinum is carried on the 
 end of a thermal couple, and this is connected to the cold 
 junction and the galvanometer. The readings of the galva- 
 nometer and the cold junction, together with the correction 
 plot of the galvanometer, will give the temperature of the 
 platinum from time to time. If the Heraeus galvanometer, 
 with the legend " Kaiser and Schmidt, Berlin," on the dial is 
 used, it should be tapped lightly with the finger or lead 
 pencil before each reading to eliminate errors due to pivot 
 friction. The temperature of the platinum in the furnace 
 should now be carried through as wide a range of tempera- 
 ture as possible, temperatures from 650 C. to 1500 C. being 
 easily maintained for a sufficient length of time to make an 
 observation. Reading of the photometer should be taken at 
 intervals of about 100 degrees. At least three runs through- 
 out the entire range should be made. Since there is but one 
 standard lamp provided, and we wish to measure tempera- 
 tures through a considerable range, we must have some 
 means of making the standard of greater or less brilliancy 
 according to the temperature range in which the temperature 
 we are measuring lies. We do this by inserting either 
 between the standard and the eyepiece, or between the hot 
 body and the eyepiece, an absorbing glass of a grayish 
 or smoky color. This alters the apparent intensity of the 
 object or the standard in a certain definite proportion The 
 
LE CH ATELIER PHOTOMETRIC PYROMETER 21 
 
 amount of the absorption is to be obtained by taking readings 
 at some fixed temperature both with and without the smoked 
 glass. This absorption factor should be determined with 
 the greatest care. All of the pieces of glass are from the 
 same sheet and have the same absorption factor, so that only 
 one piece need be examined. 
 
 No determination of the absorption factor need be made if 
 we wish to use the instrument over only such ranges of tem- 
 perature as those at which we may calibrate ; but for higher 
 temperatures we must add absorbing glasses and correct the 
 apparent intensities for the amount absorbed by the glasses. 
 For instance, suppose we have calibrated and gotten a plot 
 of the relation of temperature to readings of the scale of 
 the instrument, or rather the squares of the readings. It 
 will be noticed that the scale indicates the amount of linear 
 movement of the parts of the diaphragm, and the square of 
 the readings would indicate the relative area of the opening 
 from time to time ; hence it is better to plot the squares of the 
 readings rather than the readings themselves. Let us then 
 take an observation of the temperature of the filament of one 
 of the large incandescent lamps used to light the room. It 
 will be found necessary to insert two or three absorbing glasses, 
 in order to have a scale reading as large as five divisions, 
 which is the smallest reading which should ever be used, as 
 the precision of smaller reading is very poor. Having gotten 
 the reading with three glass, for instance, if we have only cali- 
 brated with one glass and without a glass, we must reduce 
 our reading by extrapolating, and should have to assume 
 that the relation between temperature and intensity of radia- 
 tion remains the same at higher temperatures. For further 
 discussion of this the student is referred to Le Chatelier, 
 with the suggestion that until further data can be gotten, it 
 is well to use the instrument for only such ranges as can be 
 covered by a calibration. As an indicator of changes in 
 temperature it is, of course, available over a larger range. 
 
 Each student, after calibrating and getting the necessary 
 data for a plot of squared readings and temperatures, will 
 make determinations of the melting point of copper and of 
 
22 LABORATORY OF HEAT MEASUREMENTS 
 
 one other substance, as directed by the instructor. To do 
 this it is best to put one of the small Fletcher crucible fur- 
 naces on the floor and point the photometer down into it. 
 The point where the copper melts can be readily noted as the 
 particles of oxide and slag begin to float about on the melting 
 metal. Since all substances radiate at the same temperature 
 with the same intensity, if only they be enclosed in a recep- 
 tacle at the same temperature, we may use the surface of the 
 copper and need not put the piece of platinum into the 
 furnace near the crucible. If, however, the hot body is not 
 in a receptacle at approximately its own temperature, the 
 platinum must be used. 
 
 The report should include data for the plot, the plot, and 
 the temperatures of the melting points as deduced from the 
 plot. 
 
 MESURE AND NOUEL POLARISCOPE 
 
 The change in the color of the light coming from a hot 
 body as its temperature changes, is the phenomenon upon 
 which the pyrometer of Mesure and Nouel is based. The 
 instrument is described in detail in Le Chatelier, page 158. 
 It is essentially a pyroscope rather than a pyrometer, be- 
 ing useful for the determinations of slight variations in 
 
 FIG. 6. Mesure and Nouel Polariscope. 
 
 temperature rather than for the exact measurement of the 
 temperature itself. When a body is heated it becomes 
 first red, then yellow, and finally white hot. In other 
 words, the percentage of red light is greater at the lower 
 temperatures and less as the temperature rises. The polari- 
 scope, consisting of two Nicols prisms with a quarter wave 
 plate between them, serves to determine, at least ap- 
 
MESURE AND NOUEL POLARJSCOPE 23 
 
 proximately, the percentage of red in the light from the 
 body under examination. The relative position of the two 
 Nicols necessary to so alter the light passing through them 
 as to make it of any particular color is different with 
 lights of different color, and hence for light from bodies at 
 different temperature. For instance, with a red quarter 
 wave plate we find it necessary to rotate the polarizer more 
 to cause the red to disappear from the field if the light 
 comes from a very hot body than if it comes from one at a 
 dull red heat. And this is exactly what we do in using this 
 instrument. If it be pointed at a hot body, the field is seen 
 illuminated by a red or a green light. By turning the 
 polarizer, the field may be made either red or green as we 
 like, but it will be found that the grayish color or " sensitive 
 tint " which covers the field when it is just passing from red 
 to green, or from green to red, occurs at a particular angle 
 for each particular temperature of the hot body. It is 
 necessary, therefore, to note the different angles at which the 
 sensitive tint occurs with light from sources at known 
 temperatures, and then make a calibration plot. On this 
 plot temperatures may then be found to correspond with 
 readings of unknown temperatures. 
 
 Considerable difficulty will be found at first in making 
 check readings with the polariscope, but patience and perse- 
 verance will enable one to make fair settings after fifteen or 
 twenty minutes. If one is color-blind in even the slightest- 
 degree it is impossible to use the instrument, with hope 
 of success, and students whose eyesight is defective in this 
 way are requested to notify the instructor, who will excuse 
 them from working with this pyrometer. 
 
 Each student will make a partial calibration of the polari- 
 scope and measure several unknown temperatures. The 
 calibration is to be made as in the case of the Le Chatelier 
 photometric pyrometer with the aid of a bit of platinum 
 and the thermo-electric pyrometer. The temperatures to be 
 measured will be indicated by the instructor, if possible the 
 ordinary working temperatures of the small muffles and pot 
 furnaces in the mining laboratory should be among them. 
 
24 LABORATORY OF HEAT MEASUREMENTS 
 
 MEASUREMENT OF HEAT OF COMBUSTION 
 
 There are three methods of so burning a fuel as to 
 measure its heat of combustion or calorific power : first, by 
 igniting it in a stream of oxygen ; second, by confining it in 
 a strong receptacle with sufficient oxygen to completely burn 
 it ; and third, to mix with it, before ignition, some solid which 
 will furnish oxygen when heated. The first method- gives 
 us the calorimeters of William Thomson and George Barrus ; 
 the second, the bomb calorimeter of Berthelot, Mahler, and 
 Norton ; and the third, the calorimeter of Parr using sodium 
 peroxide as an oxidizing substance, and that of Stohman and 
 Lewis Thomson using chlorate and nitrate of potassium or 
 peroxide of manganese. 
 
 Of the several pieces of apparatus available for the 
 measurement of heat of combustion, all make use of a 
 calorimeter in which to measure the heat directly. The 
 Junkers calorimeter, for the measurement of the heat of 
 combustion of gaseous and liquid fuels, is a " continuous " 
 calorimeter, the others are of the familiar "method of mix- 
 tures " type. Of the three methods, that making use of the 
 bomb is most precise, that of Professor Parr is the most con- 
 venient and most readily adaptable to the needs of engineer- 
 ing practice, while the Junkers apparatus is far better for 
 the measurement of the efficiency of gaseous fuels than any 
 of the others. 
 
 Coal 
 
 The coal from which the sample is taken should be free 
 from large lumps ; such lumps can be broken up with a 
 hammer. 
 
 After thoroughly mixing the sample, spread it out on a 
 piece of glazed paper, and take a ff grab " or hand sample, 
 here and there, until about 75 grams are obtained. If the 
 coal is already finely ground, 50 grams will suffice. 
 
 Grind this quantity in the small iron mortar until it will 
 pass the loo-mesh sieve. Pass the entire amount through 
 the screen, as otherwise it will have an undue proportion of 
 
MEASUREMENT OF HEAT OF COMBUSTION 25 
 
 the softer materials and will not be a representative sample. 
 Pour the screened coal on to glazed paper, and, after thor- 
 oughly mixing, spread it in an even layer and sample with a 
 spatula, taking enough to nearly fill a wide-mouth sample 
 tube. Place this in the drying closet at 110 C. and leave 
 there for fifteen minutes. This heating is for the purpose 
 of driving out the moisture so that water will not be weighed 
 as coal. 
 
 Weighing. 
 
 The balance used is sensitive to T V milligram and is 
 therefore delicate and must be handled carefully. 
 
 The arm is lowered on to its knife-edge by turning 
 the large knob to the left, and care must be taken not to 
 do this until approximately equivalent weights are in the 
 pans. 
 
 Whenever the substance is removed from the left-hand pan 
 or the large weights are changed, the balance arm must be 
 raised on its supports. Failure to do this may throw the 
 balance out of adjustment and permanently injure it. 
 
 Fill a small weighing tube two-thirds full of the dry coal 
 and place it on the left-hand pan of the balance. Weigh the 
 tube and coal to the nearest milligram, *'. ., the largest 
 division on the arm of the balance. 
 
 After the weight has been ascertained, raise the balance 
 arm on its supports and remove weights, corresponding to 
 the weight of coal desired, from the pan. 
 
 Pour out enough coal, a little at a time, to counterbalance 
 this change in weights until within the allowable error of 
 one milligram. 
 
 Always record the different weights of the tube and coal, 
 so that the last weighing of one sample may be used as the 
 first weighing of another, provided that no coal has been 
 spilled in the meantime. 
 
 In this way several successive weighings can be made 
 with rapidity and precision. The weights must be returned 
 to their proper places, the balance arm raised, and the slide 
 closed after every weighing. 
 
26 LABORATORY OF HEAT MEASUREMENTS 
 
 FUEL COMBUSTION BOMB 
 
 The method of measuring the heat of combustion of fuels 
 by burning them in a bomb with oxygen at high pressure 
 is due to Berthelot, and apparatus has been devised for 
 working according to this method by many experimenters. 
 Perhaps the best known bombs are those of Mahler, Donkin, 
 Atwater and Hempel. The one used in the Laboratory of 
 Heat Measurements is the result of the joint efforts of sev- 
 eral members of the instructing staff of the Institute. It 
 differs from earlier bombs in material and design, and the 
 result of six years' use in the hands of a large number of 
 students shows it to be a durable as well as a practical type 
 of instrument. It is made of aluminum-bronze, having a 
 composition of ninety parts of copper to ten parts of alumi- 
 num. The object of the use of this particular alloy is to 
 avoid the lining with platinum or enamel, which has been 
 one of tjie most troublesome features of many types of bomb. 
 This alloy is nearly or quite as strong as steel and is not 
 attacked by the oxygen under the ordinary conditions of use. 
 The object of having the joint in the centre of the bomb 
 is to insure ease of access to all parts of the inner surface 
 for cleaning. The joint is merely an enlarged plumbers' 
 union, and it is essential that it should be freely lubricated 
 iipon the shoulder upon which the nut bears, but that it 
 should be scrupulously clean on the bearing surface of the 
 lead -packing ring. The greatest care is needed to keep the 
 two faces of the upper and lower hemispheres free from 
 scratches and dents, since otherwise it will be impossible to 
 make the joint tight. The valve is essentially a delicate 
 piece of mechanism and it must not be strained. 
 
 The directions for using the apparatus are given some- 
 what briefly below. 
 
 The Bomb. 
 
 Remove the calorimeter from the jacket and put into it 
 2,000 c. c. of water at a temperature of about 4 below that 
 of the room. 
 T Open the bomb and put the pan in place; cut off about 
 
FUEL COMBUSTION BOMB 27 
 
 two inches of the platinum fuse wire and connect it so that it 
 passes from the insulated eye in the bomb, through the hole 
 in the upright piece on the pan, and across to the other side 
 of the pan. (See Fig. 7.) Be sure that the wire dips well 
 down into the pan, but does not touch the bottom. Now test 
 the fuse wire by touching one lead wire of the igniting cir- 
 cuit to the insulated plug on the outside of the bomb, and 
 the other to the bomb itself. If the platinum wire flashes 
 red, the connections are properly made. 
 
 FIG. 7. Combustion Bomb. 
 
 Weigh qnejrrarrLof rpj^ directly into the pan, and put the 
 pan in position in the bomb. Having the coal and fuse in 
 place, clamp the lower part of the bomb tightly in the socket 
 provided for it. 
 
 See that the screw and nut are scrupulously clean and well 
 oiled. Do not put oil on the lead packing ring, and see that 
 it also is clean. Put on the top half of the bomb, slip the 
 nut down over it, and see if it fits easily and turns smoothly. 
 If it does not, call the instructor. 
 
o 
 
 28 LABORATORY OF HEAT MEASUREMENTS 
 
 The bomb must be closed with a strong, steady pull, not a 
 hard jerk. Keep one foot well out to the rear, to guard 
 against the consequences of a slip of the wrench. Having 
 tightened the joint, let it stand for three or four minutes, and 
 tighten again to take up any looseness 'due to the flowing of 
 the lead packing. 
 
 Connect the copper tube of the oxygen supply with the 
 nipple at the top of the bomb, leaving the bomb valve open ; 
 turn the screw to the right to open the valve, which is "left- 
 handed," and be careful not to strain this valve, as it has 
 a very fine thread. 
 
 Let the oxygen in slowly until the gauge shows a pressure 
 oijoo pounds. Close both^ valves, tightly and uncouple the 
 tube from the bomb. Now put the bomb into the calorimeter, 
 first hooking one of the lead wires into the ring in the side 
 plug of the bomb. Be careful not to touch the other lead 
 wire to the bomb while the switch is closed, and thus prema- 
 turely fire the charge, and also not to move the bomb 
 violently enough to spill the coal out of the pan. 
 
 Put the calorimeter into the water jacket and the bomb 
 into the water ; start the stirrer and run five minutes before 
 the temperatures are read, as the bomb is probably not at the 
 temperature of the water when it is first immersed. 
 
 Insert the thermometer and read every half minute for 
 fifteen minutes. At the end of the first five minutes, ask 
 instructor to ignite the charge. The temperature should rise 
 rapidly, reaching a maximum in about two and one-half 
 minutes, and then fall slightly till the last reading is made. 
 Then stop the motor, remove the bomb from the water and 
 put back in the clamp. 
 
 % Open the valve to let the products of combustion escape, 
 and then open the bomb. 
 
 Wash out the pan and bomb and leave them clean and 
 dry. 
 
 The specific heat of the bomb is .093; that of the can 
 and stirrer is .095 . 
 
 The can and bomb can be weighed on the platform scales. 
 The weight of the stirrer is 100 grams. 
 
PARR CALORIMETER 29 
 
 The cooling correction is to be computed and allowed for 
 as directed in the third year laboratory notes on heat. 
 
 Each student will make an examination of two fuels, making 
 two combustions on each. The report should give the calorific 
 power in calories per gram and B. T. U. per pound of fuel. 
 Students must not fire the charges until instructed specifically 
 to do so, as carelessness may result in a serious explosion. 
 
 PARR CALORIMETER 
 
 The calorimeter for the measurement of heat of combus- 
 tion in which the oxygen is supplied from the decomposition 
 of sodium peroxide is due to Professor Parr and bears his 
 name. The essential parts of the apparatus, as shown in 
 Fig. 8, are the combustion chamber, the calorimeter and 
 water jacket, and a small motor to furnish power for stirring. 
 As originally planned, the ignition was to be brought about by 
 dropping a hot wire through an opening in the top of the 
 combustion chamber. This was covered by a valve which 
 closed with a spring when the bit of hot wire had been 
 dropped in. Because of a serious accident resulting from 
 the failure of the valve to close, with consequent discharge 
 of the hot contents of the combustion chamber upon the 
 hands and faces of the observers, an electric ignitor has been 
 inserted. 
 
 Setting up of the Instrument. 
 
 The calorimeter should be placed on a firm desk or table 
 and accessible to motive power which may come from a 
 small electric motor, water motor or line shafting. The 
 power needed is exceedingly slight, the smallest electric or 
 water motor being ample. The speed when transmitted to 
 the instrument should not be too high ; 50 to 100 revolutions 
 of the pulley attached to the calorimeter is sufficient. 
 
 The small rubber collar is to be slipped on the stem of the 
 thermometer, for supporting it when passed through the 
 lid of the calorimeter. It should be so placed as to bring 
 the bulb of the thermometer about half way down from the 
 top of the can. While other preparations are progressing, 
 
3O LABORATORY OF HEAT MEASUREMENTS 
 
 hang the thermometer near the calorimeter, in order to ascer- 
 tain the temperature of the room. 
 
 Fill the two-liter flask to the mark with water about 4 
 below the room temperature. The calorimeter should be 
 removed from the instrument for filling. Inside of the calori- 
 meter should be placed the deflecting collar and pivot. The 
 combustion chamber should be -perfectly dry inside and out. 
 
 To prepare the combustion chamber for filling, screw on 
 the bottom firmly, so as to avoid any possibility of admitting 
 
 FIG. 8. Parr Fuel Calorimeter. 
 
 water to the interior, then place it on a sheet of white paper. 
 
 The sodium peroxide and the small measuring cup are to 
 be kept in a glass jar, which must be kept closed. The 
 sodium peroxide must not be scattered about, and care should 
 be taken not to get it upon the clothes or hands. Keep 
 everything with which the sodium peroxide comes in contact 
 perfectly dry. 
 
 The directions for manipulation follow. After the final 
 reading in a test has been taken, dismantle by first carefully 
 removing and hanging up the thermometer. After removing 
 
PARR CALORIMETER 31 
 
 the pulley and cover, take out the calorimeter entire, then 
 remove the cartridge from the water, remove the spring clips 
 with vanes, unscrew the ends, clean them at once with a dry 
 towel, and place the cartridge under the tap or in a basin of 
 water. The contents should dissolve out rapidly and in a 
 few minutes the cartridge will be ready for rinsing and 
 drying. Dissolving the contents of the cartridge in a basin 
 has the advantage of indicating whether the combustion i,s 
 perfect or not. Of course precipitated iron and ash will 
 always be in evidence. The result is still better shown by 
 acidifying with commercial hydrochloric acid, when practi- 
 cally a clear solution should result. 
 
 Manipulation. 
 
 The coal, properly sampled, should be ground in a mortar 
 and passed through a loo-mesh sieve. The amount so 
 treated need not be large, an ounce or less being sufficient. 
 Upon a carefully counterpoised watch-glass weigh exactly 
 one-half gram and place in the oven to dry. The oven 
 should be maintained at 105 to no C. The coal will 
 be sufficiently dry in fifteen minutes, having been dried 
 previously. If, however, an accurate determination of the 
 water is desired, it should remain in the oven at the above 
 temperature for one hour and cooled in a desiccator or in 
 ground-clamped watch-glasses before weighing the second 
 time. For the calorific test the determination of the water is 
 not necessary, hence, after fifteen minutes in the oven at the 
 proper temperature, the sample is ready. Students need not 
 take time for this. To the half gram of coal, when cooled to 
 about the temperature of the hand, add in the watch-glass or 
 upon a piece of glazed paper, one measure the small 
 dipper-like measure in the glass jar of sodium peroxide. 
 Mix thoroughly and carefully with a knife or spatula. Do 
 not grind the mixture, but turn it and stir it, and be as quick 
 as possible. Put the entire mixture into the combustion 
 chamber. See that the bottom is screwed on firmly before 
 filling, and put the fine platinum fuse in place between the 
 
32 LABORATORY OF HEAT MEASUREMENTS 
 
 brass posts on the under side of the cover. It is well to 
 put the chamber on a piece of blue glazed paper so that par- 
 ticles which are spilled may readily be collected. 
 
 The measure is adjusted to hold very nearly 8^ or 9 grams 
 of sodium peroxide when tapped to settle the contents, and at 
 the same time shake off the excess at the top so that it will con- 
 form somewhat to a " struck" measure. Extreme accuracy 
 m this regard is not essential. Be sure, however, that the 
 measure has been filled to the exclusion of large cavities that 
 may tend to form. Return the measure to the glass jar at 
 once, and keep the whole covered and clamped to exclude 
 moisture. 
 
 When the mixing is complete, tap the cartridge lightly on 
 the bottom to settle the contents and to shake all the material 
 from the upper part of the cylinder. Put on the spring clips 
 with vanes. The cartridge is now ready for inserting in the 
 calorimeter. The calorimeter is made ready by standing it 
 outside the apparatus and adding thereto 2,000 cubic centi- 
 meters of distilled water which has been previously brought 
 to a temperature a little below that of the room, say about 
 4 C. This adjustment of the temperature of the water 
 should be made while it is yet in the two-liter flask. If too 
 warm, allow the tap water to flow over the flask. If too cold, 
 pour a little into a beaker and heat over a Bunsen burner, 
 or better still, if available, hold the flask under a hot water 
 faucet. Mix the water in the flask before thus roughly 
 taking the temperature. Since the average coal gives a 
 total rise of about 3 C. for \ gram, it is a simple matter to 
 know approximately what the initial temperature of the 
 water should be. It is well to make a note of the tempera- 
 ture of the room in the data of the experiment. 
 
 Pour the water into the calorimeter and lift the same into 
 the jacket. The pouring in of the water should be made 
 with the calorimeter removed, to avoid getting any moisture 
 on the outside of the calorimeter or in the air spaces. Now 
 insert the combustion chamber, adjust the cover, place the 
 thermometer so the bulb will extend about half way to the 
 bottom of the calorimeter, place the pulley on the stem, 
 
PARR CALORIMETER 33 
 
 adjust the arm carrying the igniting brushes, and connect with 
 the motor. The general arrangement of parts is shown in 
 Fig. 7. Too rapid revolving of the cartridge should be 
 avoided, 50 to 100 revolutions per minute being sufficient. 
 The cartridge should turn to the right, or as the hands of a 
 watch, thus deflecting the water currents downward. Read 
 the thermometer carefully every fifteen seconds. After five 
 minutes ignite the charge by closing the switch. The com- 
 bustion should be indicated by a rapid rise of the mercury, 
 which reaches its maximum height after about five minutes. 
 Read the thermometer every fifteen seconds to the nearest 
 ifa until ten minutes after it starts to rise. Make note of 
 the final maximum temperature and compute as follows : 
 The cooling connection should be made as indicated in the 
 Laboratory Notes on Heat in use in the third-year labora- 
 tory, and if it is so small as to be negligible, it should be so 
 stated in the report. 
 
 The difference is the actual rise " r " due to the total reac- 
 tion inside of the cartridge. Multiply "r" by the factor 
 3,100 and the product equals the calories per gram of 
 coal. 
 
 Notes. (a) The factor 3,100 is deduced as follows; 
 The water used plus the water equivalent of the metal 
 in the instrument amounts to 2,123 grams. In the reac- 
 tion, 73 per cent, of the heat is due to combustion of the 
 coal, and 27 per cent, is due to the heat of combination of 
 CO and HO,, with the sodium peroxide and monoxide. 
 
 If now \ gram of coal causes 2,123 grams of water to 
 rise "r" degrees, and if only 73 per cent, of this is due to 
 combustion, then 
 
 .73 X 2123 x 2 x f V" = heat that results from the com- 
 bustion of one gram of coal. 2 = 3100.00 x " r" 
 
 Give the calorific power in B. T. U. per pound as well as 
 in calories per gram. 
 
 (b) The moisture in " air dry " coal may vary from one to 
 fifteen or more per cent. When this quantity does not 
 exceed two or three per cent., the error introduced in the 
 reaction by not removing it would be too small to be of tech- 
 
34 LABORATORY OF HEAT MEASUREMENTS 
 
 nical consequence. It is better, however, in all cases to dry 
 the coal as directed. 
 
 (c) In the case of coke, drying is usually unnecessary. 
 Ashes, if they have been sprinkled, should of course be dried. 
 Ashes and sometimes coke ignite with difficulty. In such 
 cases add a second charge of sodium peroxide and % gram 
 of some good coal, the ijactor of which has been determined, 
 mix the two charges thoroughly by shaking, and ignite. The 
 coal will carry along the combustion of the entire mass. 
 Calculate the B. T. U. as usual and substract the B. T. U. 
 due to the coal. 
 
 ( d) The receptacle for the sodium peroxide is so arranged 
 that, with the contents of one can of sodium peroxide in the 
 bottom, there is still room in the jar for the measure .and 
 handle complete. The measure should always be replaced 
 in the jar and the cover clamped on. 
 
 (tf) Do not spill the sodium peroxide. Do not pour a 
 mixture of the sodium peroxide and coal into water. It may 
 ignite violently. When thrown into wet excelsior or damp 
 organic matter may cause ignition. If much is spilled on 
 the hands wash thoroughly at once. The fine dust that may 
 be breathed into the nostrils is harmless ; use care and com- 
 mon sense. There should be no more liability to accident 
 than in the use of any other caustic. 
 
 (y*) A sample of coal ground finely, even if carefully 
 kept in a corked bottle, slowly deteriorates. An appreciable 
 loss may be noticed after a week. As much as two per cent, 
 deterioration has been noted after six or eight weeks. Lump 
 or pea samples are not thus affected. 
 
 JUNKERS GAS CALORIMETER 
 
 The Junkers calorimeter is available for the measurement 
 of the heat of combustion, or calorific power of gas, kero- 
 'sene, and gasoline. The apparatus is illustrated in the 
 accompanying cuts. The calorimeter is of the "continuous" 
 type. It is essentially a small tubular boiler in an upright 
 position. The heat developed by the flame under the boiler 
 
JUNKERS GAS CALORIMETER 
 
 35 
 
 raises the temperature of the water as it passes through 
 the apparatus. A measurement of the amount of water 
 passing, and the amount of the temperature rise, gives us 
 at once the heat developed by the flame. This may be 
 expressed in calories, o* gram-degree C. units or in British 
 Thermal Units, the pound degree F. unit. 
 
 To set up the apparatus it is first necessary to so locate 
 the boiler that it may have a constant supply of water at a 
 nearly constant temperature. If there are great fluctuations 
 
 FIG. 9. Junkers Gas Calorimeter. 
 
 of the temperature of the supply mains, a large tank at the top 
 of the room will answer for several determinations. If it can 
 be fitted with a ball cock, as are the common tanks for house- 
 hold hot water supply, it will serve admirably. Beside con- 
 stant temperature of the water supply one other condition 
 must be maintained, that of constant " head " or pressure. 
 This is accomplished by means of the small cup, which is to 
 be kept full while the apparatus is being used. The best*way 
 to be sure that the cup is full is to keep the overflow pipe 
 dripping slightly. It is well to put this in a conspicuous place 
 so that a stopping of the overflow may be immediately noted 
 and more water supplied to the cup. The outlet pipe should 
 
36 LABORATORY OF HEAT MEASUREMENTS 
 
 be provided with a three-way-cock connection, so that the 
 water which has passed through the calorimeter may be run 
 into the tank, to be weighed or measured, or into the drain 
 as desired. It is necessary to so arrange this that the transfer 
 from tank to drain may be made quickly, as we wish to 
 begin the measurement of the water at a definite time with a 
 precision of about one second. The water may be measured 
 in calibrated flasks, but it is much better to weigh it and to 
 use a long run and a large amount of water. 
 
 The gas meter for use with this experiment may be 
 assumed to be in proper order without calibration correction. 
 If, for any reason, the meter is jarred or moved, it must be 
 emptied and refilled. The dial reads in liters, being gradu- 
 ated so that one revolution of the long pointer indicates three 
 liters. The small dial has divisions of three liters, making 
 one revolution on the large dial correspond to one division on 
 'the smaller dial. The pressure regulator must be put in the 
 pipe from the meter to the calorimeter. It is a floating 
 inverted cup which, as it fills with gas and rises in the water, 
 closes the valve through which it filled and then falls, to be 
 filled again. The pressure of the gas coming from it may 
 be regulated by adjusting weights on the top of the cup, 
 changing its tendency to sink, and the length of time for 
 which the valve remains open. The regulator should be 
 filled with water to a depth of about three inches. If gaso- 
 line or oil are to be tested instead of gas, it is, of course, not 
 necessary to use either meter or regulator, but the lamp 
 should be put under the calorimeter on platform scales, and 
 the loss of weight as the lamp burns should be noted and 
 recorded just as are the gas meter readings in the determi- 
 nation under discussion. Having gotten the meter setup, the 
 
JUNKERS GAS CALORIMETER 37 
 
 regulator filled and in position, the calorimeter filled and the 
 supply cup overflowing, the burner must be removed and 
 lighted and then clamped in position under the central tube 
 of the calorimeter. The temperature of the outlet water 
 should at once rise. Watch it carefully for several minutes 
 to see that it does not go high enough to endanger the 
 thermometer. It should be regulated in height by changing 
 ( the amount of water entering the apparatus by means of the 
 valve, which, with its dial, affords a very clos'e adjustment. 
 It is well to adjust the supply so as to have the difference 
 between the inlet and outlet temperatures about fifteen degrees. 
 Be careful never to start the fire under the boiler unless you 
 are certain that it has its normal amount of water. 
 
 No observation should be taken after the adjustment of the 
 water supply unti,l after an interval of five minutes, in which 
 the whole calorimeter may come to a condition of equilibrium. 
 The necessity of the delay in starting lies in the slowness 
 with which the condensed water begins to drip at a steady 
 rate. Observations taken within five minutes of the read- 
 justment of the gas supply are liable to be in error* because 
 of this slowness or "lag" in the drip, by several per cent. 
 The observations to be taken are the temperature of the inlet 
 and outlet water, the amount of gas or oil, and the weight 
 of water passing per minute. It is well to make a run of 
 eight minutes' duration. The gas meter should be reacPat 
 the beginning of the run and once each minute during the 
 run, so that the rate of gas supply per minute may be known. 
 The weighing of the water should be begun at a carefully 
 npted time, preferably the time at which the gas meter 
 readings are begun, and ended at the close of the stated 
 eight minutes with a precision of one or two seconds. If, in 
 an eight-minute run, we are in doubt as to the length of time 
 taken by the gas or water which has been measured, in 
 passing through the calorimeter, by an amount as gre*at as 
 two seconds we are in doubt as to the calorific power of the 
 gas by about two parts in 480, or nearly one half of one per 
 cent. This will emphasize the necessity of making a long 
 run. The thermometers may be read at such times as are 
 
38 LABORATORY OF HEAT MEASUREMENTS 
 
 convenient without disturbing the gas meter readings, but 
 at intervals not longer than thirty seconds. The drip from 
 the condensed gas is to be collected for the entire run. 
 We should have at the close of the run the following 
 observations : 
 
 L Table of inlet temperatures (30 seconds). 
 ^ Table of outlet temperatures (30 seconds). 
 v Table of gas meter readings (Start, minute intervals to 
 finish). 
 
 Weight of water passing in entire run. 
 Weight of drip, for entire run. 
 Time of start and finish. 
 
 The formula necessary for the reduction of these observa- 
 tions is as follows : 
 
 Let W = grams of water passing per minute. 
 / = average temperature of inlet water. 
 T= average temperature of outlet water. 
 G = liters of gas burned per minute. 
 d = grams of water condensed per minute. 
 H ' = heat of combustion of one liter of gas in calories. 
 
 Then: 
 
 
 G 
 
 
 The calorimeter measures directly without allowing for 
 the drip the total heat of combustion of the gas, but since 
 few heating devices condense the water in the products of 
 combustion, but allow the water to escape as steam, it is nec- 
 essary to report for commercial tests, not only upon the 
 total calorific power of the gas, but also upon its calorific 
 power when used in a gas engine or gas heater. To 
 do this it is necessary to collect the drip and to subtract 
 its latent heat of condensation from the total heat as measured 
 by the calorimeter. Since the latent heat developed by one 
 gram of water in condensing is 537 calories, it is necessary 
 to multiply the weight in grams by 537, as indicated by the 
 last term of the equation above. 
 
JUNKERS GAS CALORIMETER 39 
 
 Report. Each pair of students will make three determi- 
 nations of the calorific power of the Boston city gas. Use 
 slightly different rates of gas by changing weights on pressure 
 gauge. Make also a duplicate set of determinations of the 
 calorific -power of kerosene, burnt in an ordinary lamp and 
 in a blue-flame lamp, and of gasoline in the Barthel lanv^. 
 Report on the gas in calories per litre and also in B. T. IL 
 per cubic foot. The liquid fuels are to be reported in calories 
 per gram and B. T. U. per pound. Leave the apparatus 
 with both water and gas supply cut off, and the oil and 
 gasoline burners returned to their proper places. 
 
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