Fig. 15.Fig. 15.
Detail of air-resistance thermometer, showing method of mounting and wiring the thermometer. Parts of the wire guard and brass guard are shown, cut away so that interior structure can be seen.
Detail of air-resistance thermometer, showing method of mounting and wiring the thermometer. Parts of the wire guard and brass guard are shown, cut away so that interior structure can be seen.
The details of construction and method of installation are shown in fig. 15. Four strips of mica are inserted into four slots in a hard maple rod 12.5 centimeters long and 12 millimeters in diameter, and around each strip is wound 5 meters of double silk-covered pure copper wire (wire-gage No. 30). By means of heavy connecting wires, five of these thermometers are connected in series, giving a total resistance of the system of not far from 20 ohms. The thermometer proper is suspended between two hooks by rubber bands and these two hooks are in turn fastened to a wire guard which is attached to threaded rods soldered to the inner surface of the copper wall, thus bringing the center of the thermometer 3.4 centimeters from the copper wall. Two of these thermometers are placed in the dome of the calorimeter immediately over the shoulders of the subject, and the other three are distributed around the sides and front of the chamber. Thistype of construction gives maximum sensibility to the temperature fluctuations of the air itself and yet insures thorough protection. The two terminals are carried outside of the respiration chamber to the observer's table, where the temperature fluctuations are measured on a Wheatstone bridge.
The wall thermometers are designed for the purpose of taking the temperature of the copper wall rather than the temperature of the air. When temperature fluctuations are being experienced inside of the respiration chamber, the air obviously shows temperature fluctuations first, and the copper walls are next affected. Since in making corrections for the hydrothermal equivalent of the apparatus and for changes in the temperature of the apparatus as a whole it is desirable to know the temperature changes of the wall rather than the air, these wall thermometers were installed for this special purpose. In construction they are not unlike the thermometers used in the air, but instead of being surrounded by perforated metal they are encased in copper boxes soldered directly to the wall. Five such thermometers are used in series and, though attached permanently to the wall, they are placed in relatively the same position as the air thermometers. The two terminals are conducted through the metal walls to the observer's table, where variations in resistance are measured. The resistance of the five thermometers is not far from 20 ohms.
The resistance thermometer used for measuring the temperature of the body of the man is of a somewhat different type, since it is necessary to wind the coil in a compact form, inclose it in a pure silver tube, and connect it with suitable rubber-covered connections, so that it can be inserted deep in the rectum. The apparatus has been described in a number of publications.[9]The resistance of this system is also not far from 20 ohms, thus simplifying the use of the apparatus already installed on the observer's table.
The measurement of the temperature differences of the water-current by the electric-resistance thermometer was tried a number of years ago by Rosa,[10]but the results were not invariably satisfactory and in all the subsequentexperimenting the resistance thermometer could not be used with satisfaction. More recently, plans were made to incorporate some of the results of the rapidly accumulating experience in the use of resistance thermometers and consequently an electric-resistance thermometer was devised to meet the conditions of experimentation with the respiration calorimeter by Dr. E. F. Northrup, of the Leeds & Northrup Company, of Philadelphia. The conditions to be met were that the thermometers should take rapidly the temperature of the ingoing and outcoming water and that the fluctuations in temperature difference as measured by the resistance thermometers should be controlled for calibration purposes by the differences in temperature of the mercurial thermometers.
Fig. 16.Fig. 16.—Details of resistance thermometers for water-circuit. Upper part of figure shows a sketch of the outside of the hard-rubber case. In lower part is a section showing interior construction. Flattened lead tube wound about central brass tube contains the resistance wire. A is enlarged part of the case forming a chamber for the mercury bulb. Arrows indicate direction of flow on resistance thermometer for ingoing water.
For the resistance thermometer, Dr. Northrup has used, instead of copper, pure nickel wire, which has a much higher resistance and thus enables a much greater total resistance to be inclosed in a given space. The insulated nickel wire is wound in a flattened spiral and then passed through a thin lead tube flattened somewhat. This lead tube is then wound around a central core and the flattened portions attached at such an angle that the water passing through the tubes has a tendency to be directed away from the center and against the outer wall, thus insuring a mixing of the water. Space is left for the insertion of the mercurial thermometer. With the thermometer for the ingoing water, it was found necessary to extend the bulb somewhat beyond the resistance coil, so that the water might be thoroughly mixed before reaching the bulb and thus insure a steady temperature. Thus it was found necessary to enlarge the chamber A (fig. 16) somewhat and the tube leading out of the thermometer, so that the bulb of the thermometer itself could be placed almost directly at the opening of the exit tube. Under these conditions perfect mixing of water and constancy of temperature were obtained.
In the case of the thermometer which measured the outcoming water, the difficulty was not so great, as the outcoming water is somewhat nearer the temperature of the chamber, and the water as it leaves the thermometer passes first over the mercurial thermometer and then over the resistance thermometer. By means of a long series of tests it was found possible to adjust these resistance thermometers so that the variations in resistance were in direct proportion to the temperature changes noted on the mercurial thermometers. Obviously, these differences in resistance of the two thermometers can be measured directly with the Wheatstone bridge, but, what is more satisfactory, they are measured and recorded directly on a special type of automatic recorder described beyond.
The measurements of the temperature of the respiration chamber, of the water-current, and of the body temperature of the man, as well as the heating and cooling of the air-spaces about the calorimeter, are all under the control of the physical assistant. The apparatus for these temperature controls and measurements is all collected compactly on a table, the so-called "observer's table." At this, the physical assistant sits throughout the experiments. For convenience in observing the mercurial thermometers in the water-current and general inspection of the whole apparatus, this table is placed on an elevated platform, shown in fig. 3. Directly in front of the table the galvanometer is suspended from the ceiling and a black hood extends from the observer's table to the galvanometer itself. On the observer's table proper are all the electrical connections and at the left are the mercurial thermometers for the chair calorimeter. Formerly, when the method of alternately cooling and heating the air-spaces was used, the observer was able to open and close the water-valves without leaving the chair.
The observer's table is so arranged electrically as to make possible temperature control and measurement of either of the two calorimeters. It is impossible, however, for the observer to read the mercurial thermometers in the bed calorimeter without leaving his chair, and likewise he must occasionally alter the cooling water flowing through the outer air-spaces by going to the bed calorimeter itself. The installation of the electric-resistance thermometers connected with the temperature recorder does away with the reading of the mercurial thermometers, save for purposes of comparison, and hence it is unnecessary for the assistant to leave the chair at the observer's table when the bed calorimeter is in use. Likewise the substitution of the method of continuously cooling somewhat the air-spaces and reheating with electricity, mentioned on page 18, does away with the necessity for alternately opening and closing the water-valves of the chair calorimeter placed at the left of the observer's table.
Fig. 17.Fig. 17.—Diagram of wiring of observer's table. W1, W2, Wheatstone bridges for resistance thermometers; K1, K2, double contact keys for controlling Wheatstone circuits; S1, S2, S3, double-pole double-throw switches for changing from chair to bed calorimeter; S4, double-pole double-throw switch for changing from wall to air thermometers; G, galvanometer; R2, rheostat. 1, 2, 3, 4, 5, wires connecting with resistance-coils A B D E F anda b d e f; S2, 6-point switch for connecting thermal-junction circuits of either bed or chair calorimeter with galvanometer; S10, 10-point double-throw switch for changing heating circuits and thermal-junction circuits to either chair or bed calorimeter; R1, rheostat for controlling electric heaters in ingoing water in calorimeters; S8, double-pole single-throw switch for connecting 110-v. current with connections on table; S9, double-pole single-throw switch for connecting R1with bed calorimeter.
Of special interest are the electrical connections on the observer's table itself. A diagrammatic representation of the observer's table with its connections is shown in fig. 17. The heavy black outline gives in a general way the outline of the table proper and thus shows a diagrammatic distribution of the parts. The first of the electrical measurements necessary duringexperiments is that of the thermo-electric effect of the thermal junction systems installed on the calorimeters. To aid in indicating what parts of the zinc wall need cooling or heating, the thermal junction systems are, as has already been described, separated into four sections on the chair calorimeter and three sections on the bed calorimeter; in the first calorimeter, the top, front, rear, and bottom; in the bed calorimeter, the top, sides, and bottom.
Since heretofore it has been deemed unwise to attempt to use both calorimeters at the same time, the electrical connections are so made that, by means of electrical switches, either calorimeter can be connected to the apparatus on the table.
The thermal-junction measurements are made by a semicircular switch S7. The various points,i,ii,iii,iv, etc., are connected with the different thermal-junction systems. Thus, by following the wiring diagram, it can be seen that the connections withirun to the different binding-posts of the switch S10, which as a matter of fact is placed beneath the table. This switch S10has three rows of binding-posts. The center row connects directly with the apparatus on the observer's table, the outer rows connect with either the chair calorimeter or the bed calorimeter. The points markeda,b,d,e,f, etc., connect with the bed calorimeter and A, B, D, etc., connect with the chair calorimeter. Thus, by connecting the pointsgandiwith the two binding-posts opposite them on the switch S10, it can be seen that this connection leads directly to the pointion the switch S7, and as a matter of fact this gives direct connection with the galvanometer through the key on S7, thus connecting the thermal-junction system on one section of the bed calorimeter betweengandidirectly with the galvanometer. Similar connections from the other points can readily be followed from the diagram. The points on the switch S7indicated asi,ii,iii,iv, correspond respectively to the thermal-junction systems on the top, rear, front, and bottom of the chair calorimeter.
By following the wiring diagram of the pointv, it will be seen that this will include the connections with the thermal junctions connected in series and thus give a sum total of the electromotive forces in the thermal junctions. The pointviis connected with the thermal-junction system in the air system, indicating the differences in temperature between the ingoing and outgoing air. It will be noted that there are four sections in the chair calorimeter, while in the bed calorimeter there are but three, and hence a special switch S3is installed to insure proper connections when the bed calorimeter is in use.
This system of connecting the thermal junctions in different sections to the galvanometer makes possible a more accurate control of the temperaturesin the various parts, and while the algebraic sum of the temperature differences of the parts may equal zero, it is conceivable that there may be a condition in the calorimeter when there is a considerable amount of heat passing out through the top, for example, compensated exactly by the heat which passes in at the bottom, and while with the top section there would be a large plus deflection on the galvanometer, thus indicating that the air around the zinc wall was too cold and that heat was passing out, there would be a corresponding minus deflection on the bottom section, indicating the reverse conditions. The two may exactly balance each other, but it has been found advantageous to consider each section as a unit by itself and to attempt delicate temperature control of each individual unit. This has been made possible by the electrical connections, as shown on the diagram.
The rheostat for heating the air-spaces and the returning air-current about the zinc wall is placed on the observer's table and is indicated in the diagram as R2. There are five different sets of contact-points, marked 1, 2, 3, 4, and 5. One end of the rheostat is connected directly with the 110-volt circuit through the main switch S5. The other side of the switch S5connects directly with the point on the middle of switch S10, and when this middle point is joined with eitherfand F, direct connection is insured between all the various heating-circuits on the calorimeter in use. The various numbered points on the rheostat R2, are connected with the binding posts on S10, and each can in turn be connected withaor A,bor B, etc. The heating of the top of the chair calorimeter is controlled by the point 5 on the rheostat R2, the rear by the point 4, the front by the point 3, and the bottom by the point 2. Point 1 is used for heating the air entering the calorimeter by means of an electric lamp placed in the air-pipe, as shown in fig. 25.
The warming of the electrical reheater placed in the water-circuit just before the water enters the calorimeter is done by an electrical current controlled by the resistance R1. This R1is connected on one end directly with the 110-volt circuit and the current leaving it passes through the resistance inside the heater in the water-current. The two heaters, one for each calorimeter, are indicated on the diagram above and below the switch S9. The disposition of the switches is such as to make it possible to use alternately the reheaters on either the bed or the chair calorimeter, and the main resistance R1suffices for both.
For use in measuring the temperature of the air and of the copper wall of the calorimeters, as well as the rectal temperature of the subject, a seriesof resistance thermometers is employed. These are so connected on the observer's table that they may be brought into connection with two Wheatstone bridges, W1and W2. Bridge W1is used for the resistance thermometers indicating the temperature of the wall and the air. Bridge W2is for the rectal thermometer. Since similar thermometers are inserted in both calorimeters, it is necessary to introduce some switch to connect either set at will and hence the double-throw switches S1, S2, and S3allow the use of either the wall, air, or rectal thermometer on either the bed or chair calorimeter at will. Since the bridge W1is used for measuring the temperature of both the wall and the air, a fourth double-pole switch, S4, is used to connect the air and wall thermometers alternately. The double-contact key, K1, is connected with the bridge W1and is so arranged that the battery circuit is first made and subsequently the galvanometer circuit. A similar arrangement in K2controls the connections for the bridge W2.
The galvanometer is of the Deprez-d'Arsonval type and is extremely sensitive. The sensitiveness is so great that it is desirable to introduce a resistance of some 500 ohms into the thermal-junction circuits. This is indicated at the top of the diagram near the galvanometer. The maximum sensitiveness of the galvanometer is retained when the connection is made with the Wheatstone bridges. The galvanometer is suspended from the ceiling of the calorimeter laboratory and is free from vibration.
To vary the current passing through the manganin heating coils in the air-spaces next the zinc wall, a series of resistances is installed connected directly with the rheostat R2in fig. 17. The details of these resistances and their connection with the rheostat are shown in fig. 18. The rheostat, which is in the right part of the figure, has five sliding contacts, each of which can be connected with ten different points. One end of the rheostat is connected directly with the 110-volt circuit. Beneath the observer's table are fastened the five resistances, which consist of four lamps, each having approximately 200 ohms resistance and then a series of resistance-coils wound on a long strip of asbestos lumber, each section having approximately 15 ohms between the binding-posts. A fuse-wire is inserted in each circuit to protect the chamber from excessive current. Of these resistances, No. 1 is used to heat the lamp in the air-current shown in fig. 25, and consequently it has been found advisable to place permanently a second lamp in series with the first, but outside of the air-pipe, so as to avoid burning out the lamp inside of the air-pipe. The other four resistances, 2, 3, 4, and 5, are connected with the different sections on the two calorimeters. No. 5 corresponds to the top of both calorimeters. No. 4 correspondsto the rear section of the chair calorimeter and to the sides of the bed calorimeter. No. 3 corresponds to the front of the chair calorimeter and is without communication with the bed calorimeter. No. 2 connects with the bottom of both calorimeters.
It will be seen from the diagrams that each of these resistances can be connected at will with either the bed or the chair calorimeter and at such points as are indicated by the lettering below the numbers. Thus, section 1 can be connected with either the point A or pointaon fig. 17 and thus directly control the amount of current passing through the corresponding resistance in series with the lamp in the air-current. The sliding contacts at present in use are ill adapted to long-continued usage and will therefore shortly be substituted by a more substantial instrument. The form of resistance using small lamps and the resistance wires wound on asbestos lumber has proven very satisfactory and very compact in form.
Fig. 18.—Diagram of rheostat and resistances in series with it. At the right are shown the sliding contacts, and in the center places for lamps used as resistances, and to left the sections of wire resistances.Fig. 18.—Diagram of rheostat and resistances in series with it. At the right are shown the sliding contacts, and in the center places for lamps used as resistances, and to left the sections of wire resistances.
The numerous electrical, thermometric, and chemical measurements necessary in the full conduct of an experiment with the respiration calorimeter has often raised the question of the desirability of making at least a portion of these observations more or less automatic. This seems particularly feasible with the observations ordinarily recorded by the physical observer. These observations consist of the reading of the mercurial thermometers indicating the temperatures of the ingoing and outcoming water, recordswith the electric-resistance thermometers for the temperature of the air and the walls and the body temperatures, and the deflections of the thermo-electric elements.
Numerous plans have been proposed for rendering automatic some of these observations, as well as the control of the heating and cooling of the air-circuits. Obviously, such a record of temperature measurements would have two distinct advantages: (1) in giving an accurate graphic record which would be permanent and in which the influence of the personal equation would be eliminated; (2) while the physical observer at present has much less to do than with the earlier form of apparatus, it would materially lighten his labors and thereby tend to minimize errors in the other observations.
The development of the thread recorder and the photographic registration apparatus in recent years led to the belief that we could employ similar apparatus in connection with our investigations in this laboratory. To this end a number of accurate electrical measuring instruments were purchased, and after a number of tests it was considered feasible to record automatically the temperature differences of the ingoing and outcoming water from the calorimeter. Based upon our preliminary tests, the Leeds & Northrup Company of Philadelphia, whose experience with such problems is very extended, were commissioned to construct an apparatus to meet the requirements of the respiration calorimeter. The conditions to be met by this apparatus were such as to call for a registering recorder that would indicate the differences in temperature between the ingoing and outcoming water to within 0.5 per cent and to record these differences in a permanent ink line on coordinate paper. Furthermore, the apparatus must be installed in a fixed position in the laboratory, and connections should be such as to make it interchangeable with any one of five calorimeters.
After a great deal of preliminary experimenting, in which the Leeds & Northrup Company have most generously interpreted our specifications, they have furnished us with an apparatus which meets to a high degree of satisfaction the conditions imposed. The thermometers themselves have already been discussed. (See page 30.) The recording apparatus consists of three parts: (1) the galvanometer; (2) the creeper or automatic sliding-contact; (3) the clockwork for the forward movement of the roll of coordinate paper and to control the periodic movement of the creeper.
Under ordinary conditions with rest experiments in the chair calorimeter or bed calorimeter, the temperature differences run not far from 2° to 4°. Thus, it is seen that if the apparatus is to meet the conditions of the specifications it must measure differences of 2° C. to within 0.01° C. Provision has also been made to extend the measurement of temperature differences with the apparatus so that a difference of 8° can be measured with the same percentage accuracy.
The apparatus depends fundamentally upon the perfect balancing of the two sides of a differential electric circuit. A conventional diagram, fig. 19, gives a schematic outline of the connections. The two galvanometer coils,flandfr, are wound differentially and both coils most carefully balanced so that the two windings have equal temperature coefficients. This is done by inserting a small shunty, parallel with the coilfl, and thus the temperature coefficient offlandfrare made absolutely equal. The two thermometers are indicated as T1and T2and are inserted in the ingoing and outgoing water respectively. A slide-wire resistance is indicated by J, andris the resistance for the zero adjustment. Ba, Z, and Z1are the battery and its variable series resistances. If T1and T2are exactly of the same temperature,i. e., if the temperature difference of the ingoing and outcoming water is zero, the sliding contactqstands at 0 on the slide-wire and thus the resistance of the system from 0 throughfl,r, and T1back to the point C is exactly the same as the resistance of the slide-wire J plus the coilfrplus T2back to the point C. A rise in temperature of T2gives an increase of resistance in the circuit and the sliding contactqmoves along the slide-wire toward J maximum until a balance is obtained.
Fig. 19.—Diagram of wiring of differential circuit with its various shunts, used in connection with resistance thermometers on water-circuit of bed calorimeter.Fig. 19.—Diagram of wiring of differential circuit with its various shunts, used in connection with resistance thermometers on water-circuit of bed calorimeter.
Provision is made for automatically moving the contactqby electrical means and thus the complete balance of the two differential circuits is maintained constant from second to second. As the contactqis moved, it carries with it a stylographic pen which travels in a straight line over a regularly moving roll of coordinate paper, thus producing a permanently recorded curve indicating the temperature differences. The slide-wire J is calibrated so that any inequalities in the temperature coefficient of the thermometer wires are equalized and also so that any unit-length on the slide-wire taken at any point along the temperature scale represents a resistance equal to the resistance change in the thermometer for that particular change in temperature. With the varying conditions to be met with in this apparatus, it is necessary that varying values should beassigned at times to J and tor. This necessitates the use of shunts, and the recording range of the instrument can be easily varied by simple shunting,i. e., by changing the resistance value of J andr, providing these resistances unshunted have a value which takes care of the highest obtained temperature variations.
Fig. 19 shows the differential circuit complete with all its shunts. S is a fixed shunt to obtain a range on J; S' is a variable shunt to permit very slight variations of J within the range to correct errors due to changing of the initial temperatures of the thermometers;yis a permanent shunt across the galvanometer coilfl, to make the temperature coefficients offlandfrabsolutely equal; Z is the variable resistance in the battery-circuit to keep the current constant;ris a permanent resistance to fix the zero on varying ranges; S'' plus S1constitutes a variable shunt to permit slight variations ofrto finally adjust 0 after S' is fixed andtis a permanent shunt across the thermometer T1to make the temperature coefficient of T1equal to that of T2.
The apparatus can be used for measuring temperature differences from 0° to 4° or from 0° to 8°. When on the 0° to 8° range, the shunt S is open-circuited and the shunt S' alone used. The value of S, then, is predetermined so as to affect the value of the wire J and thus halve its influence in maintaining the balance. Similarly, when the lower range,i. e., from 0° to 4°, is used, the resistanceris employed, and when the higher range is used another value tormust be given by using a plug resistance-box, in the use of which the resistanceris doubled.
The resistance S'' and S1are combined in a slide-wire resistance-box and are used to change the value of the whole apparatus when there are marked changes in the position of the thermometric scale. Thus, if the ingoing water is at 2° C. and the outcoming water at 5° C. in one instance, and in another instance the ingoing water is 13° and the outgoing water is 15°, a slight alteration in the value of S1, and also of S', is necessary in order to have the apparatus draw a curve to represent truly the temperature differences. These slight alterations are determined beforehand by careful tests and the exact value of the resistances in S' and in S1are permanently recorded for subsequent use.
The galvanometer is of the Deprez-d'Arsonval type and has a particularly powerful magnetic field, in which a double coil swings suspended similar to the marine galvanometer coils. This coil is protected from vibrations by an anti-vibration tube A, fig. 20, and carries a pointer P which acts to select the direction of movement of the recording apparatus, the movable contact pointq, fig. 19. In front of this galvanometer coil and inclosed in the same air-tight metal case is the plunger contact Pl, fig. 21. The galvanometerpointer P swings freely below the silver contacts S1and S2, just clearing the ivory insulatori. The magnet plunger makes a contact depending upon the adjustment of a clock at intervals of 2 seconds. So long as both galvanometer coils are influenced by exactly the same strength of current, the pointer will stand in line with and immediately belowiand no current passes through the recording apparatus. Any disturbance of the electrical equilibrium causes the pointer P to swing either toward S1or S2, thus completing the circuit at either the right hand or the left hand, at intervals of 2 seconds. The movement of the pointer away from its normal position exactly beneathito either S1on the left hand or S2on the right, results from an inequality in the current flowing through the two coils in the galvanometer. The difference in the two currents passing through these coils is caused by a change in temperatures of the two thermometers in the water circuit.
Fig. 20.—Diagram of galvanometer coil used in connection with recording apparatus for resistance thermometers in the water-circuit of bed calorimeter. A, anti-vibration tube; P, pointer.Fig. 20.—Diagram of galvanometer coil used in connection with recording apparatus for resistance thermometers in the water-circuit of bed calorimeter. A, anti-vibration tube; P, pointer.
The movement of the sliding-contactq, fig. 19, along the slide-wire J, is produced by means of a special device called a creeper, consisting of a piece of brass carefully fitted to a threaded steel rod some 30 centimeters long. The movement of this bar along this threaded rod accomplishes two things.The bar is in contact with the slide-wire J and therefore varies the position of the pointqand it also carries with it a stylographic pen. The movements of this bar to the right or the left are produced by an auxiliary electric current, the contact of which is made by a plunger-plate forcing the pointer P against either S1or S2. P makes the contact between Pl and either S1or S2and sends a current through solenoids at either the right or the left of the creeper. At intervals of every 2 seconds the plunger rises and forces the pointer P against either S1,i, or S2above. The movement of this plunger is controlled by a current from a 110-volt circuit, the connections of which are shown in fig. 22. If the contact is made at T, the current passes through 2,600 ohms, directly across the 110-volt circuit, and consequently there is no effective current flowing through the plunger Pl. When the contact T is open, the current flows through the plunger in series with 2,600 ohms resistance. T is opened automatically at intervals of 2 seconds by the clock.
Fig. 21.—Diagram of wiring of circuits actuating plunger and creeper.Fig. 21.—Diagram of wiring of circuits actuating plunger and creeper.
Fig. 22.—Diagram of wiring of complete 110-volt circuit.Fig. 22.—Diagram of wiring of complete 110-volt circuit.
The movement of the contact arm along the threaded rod is produced by the action of either one of two solenoids, each of which has a core attached to a rack and pinion at either end of the rod. If the current is passed through the contact S1, a current passes through the left-hand solenoid, the core moves down, the rack on the core moves the pinion on the rod through a definite fraction of a complete revolution and this movement forces the creeper in one direction. Conversely, the passing of the current through the solenoid at the other end of the threaded rod moves the creeper in the other direction. The distance which the iron rack on the end of the core is moved is determined carefully, so that the threaded rod is turned for each contact exactly the same fraction of a revolution. For actuating these solenoids, the 110-volt circuit is again used. The wire connections are shown in part in fig. 21, in which it is seen that the current passes through the plunger-contact and through the pointer P to the silver plate S1andthen along the line G1through 350 ohms wound about the left-hand solenoid back through a 600-ohm resistance to the main line. The use of the 110-volt current under such circumstances would normally produce a notable sparking effect on the pointer P, and to reduce this to a minimum there is a high resistance, amounting to 10,000 ohms on each side, shunted between the main line and the creeper connections. This shunt is shown in diagram in fig. 22. Thus there is never a complete open circuit and sparking is prevented.
The clock requires winding every week and is so geared as to move the paper forward at a rate of 3 inches per hour. The contact-point for opening the circuit T on fig. 22 is likewise connected with one of the smaller wheels of the clock. This contact is made by tripping a little lever by means of a toothed wheel of phosphor-bronze.
Fig. 23Fig. 23Temperature recorder. The recorder with the coordinate paper in the lower box with a glass door. A curve representing the temperature difference between the ingoing and outgoing water is directly drawn on the coordinate paper. Above are three resistance boxes, and the switches for electrical connections are at the right. On the top shelf is the galvanometer, and immediately beneath, the plug resistance box for altering the value of certain shunts.
Fig. 24.—Detailed wiring diagram showing all parts of recording apparatus, together with wiring to thermometers complete, including all previous figures.Fig. 24.—Detailed wiring diagram showing all parts of recording apparatus, together with wiring to thermometers complete, including all previous figures.
The whole apparatus is permanently and substantially installed on the north wall of the calorimeter laboratory. A photograph showing the various parts and their installation is given in fig. 23. On the top shelf is seen the galvanometer and on the lower shelf the recorder with its glass door in front and the coordinate paper dropping into the box below. The curve drawn on the coordinate paper is clearly shown. Above the recorder are the resistance-boxes, three in number, the lower one at the left being the resistance S1, the upper one at the left being the resistance S', and the upper one at the right being the resistance Z1. Immediately above the resistance-box Z1is shown the plug resistance-box which controls on the one hand the resistancerand on the other hand the resistance S, both of which are substantially altered when changing the apparatus to register from the 0° to 4° scale to the 0° to 8° scale. A detailed wiring diagram is given in fig. 24.
Fig. 25.Fig. 25.—Section of calorimeter walls and part of ventilating air-circuit, showing part of pipes for ingoing air and outgoing air. On the ingoing air-pipe at the right is the lamp for heating the ingoing air. Just above it, H is the quick-throw valve for shutting off the tension equalizer IJ. I is the copper portion of the tension equalizer, while J is the rubber diaphragm; K, the pet-cock for admitting oxygen; F, E, G, the lead pipe conducting the cold water for the ingoing air; and C, the hair-felt insulation. N, N are brass ferules soldered into the copper and zinc walls through which air-pipes pass; M, a rubber stopper for insulating the air-pipe from the calorimeter; O, the thermal junctions for indicating differences of temperature of ingoing and outgoing air and U, the connection to the outside; QQ, exits for the air-pipes from the box in which thermal junctions are placed; P, the dividing plate separating the ingoing and outgoing air; R, the section of piping conducting the air inside the calorimeter; S, a section of piping through which the air passes from the calorimeter; A, a section of the copper wall; Y, a bolt fastening the copper wall to the 2-1/2 inch angle W; B, a portion of zinc wall; C, hair-felt lining of asbestos wall D; T-J, a thermal junction in the walls.
In passing the current of air through the calorimeter, temperature conditions may easily be such that the air entering is warmer than the outcoming air, in which case heat will be imparted to the calorimeter, or the reverse conditions may obtain and then heat will be brought away. To avoid this difficulty, arrangements are made for arbitrarily controlling the temperature of the air as it enters the calorimeter. This temperature control is based upon the fact that the air leaving the chamber is caused to pass over the ends of a series of thermal junctions shown as O in fig. 25. These thermal junctions have one terminal in the outgoing air and the other in the ingoing air, and consequently any difference in the temperature of the two air-currents is instantly detected by connecting the circuit with the galvanometer. Formerly the temperature control was made a varying one, by providing for either cooling or heating the ingoing air as the situation called for. The heating was done by passing the current through anelectric lamp placed in the cross immediately below the tension equalizer J. Cooling was effected by means of a current of water through the lead pipe E closely wrapped around the air-pipe, water entering at F and leaving at G. This lead pipe is insulated by hair-felt pipe-covering, C. More recently, we have adopted the procedure of passing a continuous current of water, usually at a very slow rate, through the lead pipe E and always heating the air somewhat by means of the lamp, the exact temperature control being obtained by varying the heating effect of the lamp itself. This has been found much more satisfactory than by alternating from the cooling system to the heating system. In the case of the air-current, however, it is unnecessary to have the drop-sight feed-valve as used for the wall control, shown in fig. 13.
During experiments with man not all the heat leaves the body by radiation and conduction, since a part is required to vaporize the water from the skin and lungs. An accurate measurement of the heat production by man therefore required a knowledge of the amount of heat thus vaporized. One of the great difficulties in the numerous forms of calorimeters that have been used heretofore with man is that only that portion of heat measured by direct radiation or conduction has been measured and the difficulties attending the determination of water vaporized have vitiated correspondingly the estimates of the heat production. Fortunately, with this apparatus the determinations of water are very exact, and since the amount of water vaporized inside the chamber is known it is possible to compute the heat required to vaporize this water by knowing the heat of vaporization of water.
Since the earlier reports describing the first form of calorimeters were written, there has appeared a research by one of our former associates, Dr. A. W. Smith[11]who, recognizing the importance of knowing exactly the heat of vaporization of water at 20°, has made this a special object of investigation. When connected with our laboratory a number of experiments were made by Doctors Smith and Benedict in an attempt to determine the heat of vaporization of water directly in a large calorimeter; but for lack of time and pressure of other experimental work it was impossible to complete the investigation. Subsequently Dr. Smith has carried out the experiments with the accuracy of exact physical measurements and has given us a very valuable series of observations.
Using the method of expressing the heat of vaporization in electrical units, Smith concludes that the heat of vaporization of water between 14° and 40° is given by the formula
L (in joules) = 2502.5 - 2.43T
and states that the "probable error" of values computed from this formula is 0.5 joule. The results are expressed in international joules, that is, in terms of the international ohm and 1.43400 for the E.M.F. of the Clark cell at 15° C., and assuming that the mean calorie is equivalent to 4.1877 international joules,[12]the formula reads
L (in mean calories) = 597.44 - 0.580T
With this formula Smith calculates that at 15° the heat of vaporization of water is equal to 588.73 calories; at 20°, 585.84 calories; at 25°, 582.93 calories; at 30°, 580.04 calories;[13]and at 35°, 577.12 calories. In all of the calculations in the researches herewith we have used the value found by Smith as 586 calories at 20°. Inasmuch as all of our records are in kilo-calories, we multiply the weight of water by the factor 0.586 to obtain the heat of vaporization.
The chair calorimeter was designed for experiments to last not more than 6 to 8 hours, as a person can not remain comfortably seated in a chair much longer than this time. For longer experiments (experiments during the night and particularly for bed-ridden patients) a type of calorimeter which permits the introduction of a couch or bed has been devised. This calorimeter has been built, tested, and used in a number of experiments with men and women. The general shape of the chamber is given in fig. 26. The principles involved in the construction of the chair calorimeter are here applied,i. e., the use of a structural-steel framework, inner air-tight copper lining, outer zinc wall, hair-felt insulation, and outer asbestos panels. Inside of the chamber there is a heat-absorbing system suspended from the ceiling, and air thermometers and thermometers for the copper wall are installed at several points. The food-aperture is of the same general type and the furniture here consists simply of a sliding frame upon which is placed an air-mattress. The opening is at the front end of the calorimeter and is closed by two pieces of plate glass, each well sealed into place by wax after the subject has been placed inside of the chamber. Tubes through the wall opposite the food-aperture are used for the introduction of electrical connections, ingoing and outgoing water, the air-pipes, and connections for the stethoscope, pneumograph, and telephone.
The apparatus rests on four heavy iron legs. Two pieces of channel iron are attached to these legs and the structural framework of the calorimeter chamber rests upon these irons. The method of separating the asbestos outer panels is shown in the diagram. In order to provide light for thechamber, the outer wall in front of the glass windows is made of glass rather than asbestos. The front section of the outer casing can be removed easily for the introduction of a patient.
In this chamber it is impossible to weigh the bed and clothing, and hence this calorimeter can not be used for the accurate determination of the moisture vaporized from the lungs and skin of the subject, since here (as in almost every form of respiration chamber) it is absolutely impossible to distinguish between the amount of water vaporized from bed-clothing and that vaporized from the lungs and skin of the subject. With the chair calorimeter, the weighing arrangements make it possible to weigh the chair, clothing, etc., and thus apportion the total water vaporized between losses from the chair, furniture, and body of the man. In view of the fact that the water vaporized from the skin and lungs could not be determined, the whole interior of the chamber of the bed calorimeter has been coated with a white enamel paint, which gives it a bright appearance and makes it much more attractive to new patients. An incandescent light placed above the head at the front illuminates the chamber very well, and as a matter of fact the food-aperture is so placed that one can lie on the cot and actually look outdoors through one of the laboratory windows.