Abstract:
A calorimeter includes a bucket cover which is used to reconfigure an isothermal water reservoir to provide for temperature equilibration prior to sample analysis and subsequently define a fixed volume of water during analysis in which high precision temperature measurements can be recorded. The apparatus includes mechanisms for sealing and controlling the cover, and for coupling the combustion vessel to the cover while minimizing the thermal contact between them. Improved thermal isolation between the fixed volume of water and the surrounding environment is also achieved.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 11/766,313, filed on Jun. 21, 2007 now U.S. Pat. No. 7,481,575, entitled CALORIMETER, which was a continuation-in-part of U.S. patent application Ser. No. 11/416,970 filed on May 3, 2006 now U.S. Pat. No. 7,488,106, entitled C ALORIMETER , the entire disclosures of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a calorimeter including a combustion vessel and an integrated isothermal fluid reservoir. 
     In the past, somewhat complicated apparatus has been employed for the determination of the calorific value of solid and liquid substances in accordance with standard methodology (ASTM/ISO standards). The operation of such an apparatus is well understood and has been described in, for example, the American National Standard Institute ANSI/ASTM D5865. 
     Prior calorimeters have required the use of multiple internal and external reservoirs with which to contain and manage the water required to operate the apparatus. U.S. Pat. Nos. 4,398,836 and 4,616,938 disclose calorimeters which have a tank for holding a calorimeter combustion vessel and a separate water tank coupled by conduits and valves for supplying water to the vessel. In another calorimeter disclosed in U.S. Pat. No. 4,616,938, two distinct reservoirs were employed, including an internal jacket reservoir and a permanent internal bucket reservoir. In another calorimeter disclosed in U.S. Pat. No. 5,322,360, four distinct water reservoirs are employed: 
     1) A first internal reservoir, commonly referred to as a jacket, is employed to provide a constant isothermal environment. 
     2) A second internal reservoir is employed to provide a ballast volume of water from which to fill an external burette. 
     3) A third external reservoir, commonly referred to as a burette, is employed to deliver a reproducible amount of analysis water. 
     4) A fourth transportable reservoir, commonly referred to as a bucket, is used to receive the water delivered from the burette and to contain the combustion vessel. The bucket is installed in the analyzer and temperature measurements of the bucket are recorded during the course of the analysis. 
     One disadvantage of using separate reservoirs in a calorimeter is that, during routine operation, the systems require an external source of coolant water to eliminate thermal energy generated by the combustion of the sample. Also, the use of multiple reservoirs in such prior art systems requires numerous valves and conduits with which to direct the water to and from the reservoirs. 
     The operation of prior art isothermal calorimeters is further complicated by the requirement to maintain the temperature of the water substantially constant in all reservoirs from one analysis to the next. Additionally, upon the completion of an analysis, any heat resultant from the combustion of the sample must be removed. 
     Furthermore, prior art designs required the use of a distinctly separate bucket reservoir in order to ensure that the volume of water contained therein be maintained substantially constant from one analysis to the next. This requirement is a result of the fact that any variation in this volume is proportionally related to imprecision in the observed results. Assuming no other source of error, a variation of 1 part in 1000 in the volume of water will limit the precision of the apparatus, correspondingly, to 1 part in 1000. 
     Various instrument design approaches have been used to reduce this source of error. Typically, these approaches employ either a sensor or an overflow port with which to limit the volume of the water. Among other factors, such approaches are dependant either upon the surface tension of the water or the sensitivity and reproducibility of the sensor. In order to eliminate heat resultant from the combustion of the sample, these approaches require that the water in the bucket be substantially drained and refilled before each analysis. In some cases, the bucket and the combustion vessel must be dried by the operator in order to ensure that the correct volume of water is present. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, an improved apparatus and method has been developed for determining the calorific value of combustible substances. The apparatus employs a cover, which can be used to partition a single isothermal reservoir into an outer jacket and an internal bucket for receiving the calorimeter vessel. The apparatus improves the thermal isolation between the combustion vessel and the surrounding environment to achieve more accurate results. 
     In one embodiment of the invention, a calorimeter system including an isothermal reservoir includes a combustion vessel; an outer jacket having a wall, a fluid inlet and an overflow outlet located near an upper end; a system for circulating fluid from said fluid inlet to provide a constant temperature of fluid within said jacket; a thermally insulated bucket positioned within said jacket in spaced relationship to the wall thereof and having an internal volume therein defining a bucket for receiving a calorimeter combustion vessel, said bucket having a height less than the height of said jacket such that fluid in said jacket fills said bucket; and a movable bucket cover coupled to said calorimeter combustion vessel and including a seal engaging said bucket for sealing said bucket from said jacket during combustion of a sample within said combustion vessel. 
     In another embodiment of the invention, a calorimeter including a combustion vessel and an isothermal reservoir for receiving said combustion vessel is provided and includes a lifting arm coupled to a bucket cover and to said combustion vessel for raising and lowering said combustion vessel into a bucket. 
     In one embodiment of the invention, the bucket cover includes an inflatable peripheral seal engaging the inner wall of the bucket to isolate the bucket from the remainder of the surrounding isothermal jacket during combustion of a sample. 
     In one embodiment also, the bucket cover includes a lower section with a quick disconnect coupling cooperating with the combustion vessel cover to minimize the thermal communication between the bucket cover and combustion vessel. 
     In order to further thermally isolate the bucket and the isothermal reservoir or jacket in one embodiment, a stirrer is included in the bucket and has two permanent magnets mounted on either side of its rotary axis which are magnetically coupled to a secondary rotary magnet drive positioned outside of the isothermal jacket to provide thermal isolation between the bucket and the jacket. 
     In order to raise and lower an arm holding the bucket cover and the combustion vessel, the arm is mounted to a vertically movable post which is guidably and movably supported on a vertically fixed stanchion by roller couplings. The movable post includes a support bracket which rests upon the thrust nut of a screw drive, such that the screw drive urges the movable post, bucket cover, and combustion vessel upwardly between a fully lowered immersed position to intermediate and raised positions for access to the combustion vessel. As the screw drive is reversed, the movable post lowers by gravity with the support bracket resting upon the thrust nut assembly. In the event the movable post does not follow the thrust nut in its lowering motion and the bracket and thrust nut assembly separate, a spring-loaded pawl has a locking end which engages a toothed rack on the stanchion for holding the combustion vessel supporting arm in a fixed position, thereby preventing it from uncontrollably dropping into the bucket. 
     These and other features, objects and advantages of the present invention will become apparent upon reading the following description thereof together with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective front right view of a calorimeter embodying the present invention; 
         FIG. 2  is a left side elevational view, partially in vertical cross section, of the calorimeter embodying the present invention, shown with the calorimeter combustion vessel in a raised position; 
         FIG. 3  is a front vertical cross-sectional view of the calorimeter embodying the present invention, shown with the calorimeter combustion vessel immersed in the bucket of the isothermal reservoir; 
         FIG. 4  is a right side elevational view in vertical cross section of the calorimeter with the calorimeter vessel raised from the isothermal reservoir; 
         FIG. 5  is an enlarged fragmentary front vertical cross section, showing the combustion vessel immersed during an analysis, and showing the coupling of the combustion vessel to the bucket cover; 
         FIG. 6  is a fragmentary perspective view, partly in phantom, of the structure shown in  FIG. 5 , shown with the calorimeter vessel in a raised position for access; 
         FIGS. 7A-7C  are enlarged fragmentary perspective views of the structure coupling the combustion vessel and the bucket cover; 
         FIGS. 8A-8C  are fragmentary perspective views of the raising and lowering mechanism for the calorimeter vessel; 
         FIG. 9  is a schematic view of the calorimeter including a flow diagram of the fluid components of the calorimeter; 
         FIG. 10  is a flow diagram showing the steps in the sequence of operation of the calorimeter of the present invention; and 
         FIG. 11  is a block electrical circuit diagram of the control system for the calorimeter. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring initially to  FIGS. 1-4 , there is shown a calorimeter  10  embodying the present invention. The calorimeter is shown in  FIGS. 1 ,  2 , and  4  in an open position for loading and removal of the combustion vessel  20  for introducing a sample, installing the ignition fuse, and filling the vessel with combustion oxygen. In  FIG. 3 , the calorimeter is shown in a closed position with the combustion vessel  20  immersed in an isothermal reservoir during an analysis. The calorimeter combustion vessel  20  is made of stainless steel about 0.25 inches thick with a top  25  sealably engaging the bullet-shaped curved blunt enclosed lower end  28  and is retained by a threaded closure ring  26 . 
     Calorimeter  10  includes a cabinet  12 , as seen in  FIG. 1 , enclosing frame members which support the components of the calorimeter, including the fluid connections as illustrated in  FIG. 9  and described below. Cabinet  12  also houses the internal components of the calorimeter as well as electrical components and coupling to an external microprocessor, display, and printer, as illustrated in  FIG. 11 . The combustion vessel  20  is coupled to a bucket cover  30  which, in turn, is coupled to an arm  14  by a hollow cylindrical tube  16  through which the electrical connections for firing the fuse of the combustion vessel  20  is provided, as well as a communication path for pneumatic pressure for inflating the seal associated with cover assembly  30  and water circulation, as described below. The arm  14  has internal conventional support framework for holding and coupling the arm  14  to a vertically movable post  40  which is coupled to a fixed stanchion  50  by the roller mechanism described below in  FIGS. 8A-8C . 
     Post  40  includes a generally L-shaped support bracket  42  having a flange  43  ( FIGS. 4 , and  8 A- 8 C) which rests upon a thrust nut assembly  46  driven by a threaded screw jack  44 , as best seen in  FIGS. 8A-8C . Screw jack  44  is rotated by a drive motor  48  to raise post  40  and the calorimeter vessel  20  coupled to arm  14  through bucket cover  30 . Reversing the screw jack  44  lowers the thrust nut assembly  46  allowing the post  40  and arm  14  holding the calorimeter vessel to lower under the influence of gravity to an intermediate position, partially submerged within the isothermal bucket  60  during an intermediate step or fully immersed into the bucket  60 , as shown in  FIGS. 3 and 5 , during an analysis. In the event the post  40  for some reason does not smoothly follow the lowering thrust nut assembly  46 , the protective ratchet mechanism shown and described below in connection with  FIGS. 8A-8C  is employed to prevent the combustion vessel from dropping into the bucket  60 . 
     The isothermal reservoir of the calorimeter  10  comprises an outer jacket  70  ( FIGS. 3 ,  4 , and  9 ) into which the isothermal bucket  60  receiving the combustion vessel  20  is mounted by thermally isolating blocks  72  ( FIG. 3 ). Water fills the jacket  70  to a level indicated by water line  57  in the drawings. Bucket  60  includes an inner stainless steel wall  62 , an outer stainless steel wall  64 , and a floor  66 ,  66 ′. The space between walls  62  and  64  and floor sections  66 ,  66 ′ are filled with foam insulation  63  to insulate the bucket from the surrounding isothermal reservoir defined by the interior volume  71  of jacket  70  during combustion of a sample once temperature equilibrium has been reached. Foam insulation  63  is contained between inner walls  62  and outer walls  64  of bucket  60 , as best seen in  FIG. 5 . The floors  66 ,  66 ′ are sealed to walls  62 ,  64  by sealing gaskets  67 ,  67 ′. The bucket  60  includes an internal baffle  80  which is generally cylindrical and has inwardly tapered lower walls  82  which are sealably coupled to an impeller  84  for circulating water around the combustion vessel  20  within bucket  60  during combustion of a sample to quickly equilibrate the water temperature within bucket  60 . 
     Impeller  84  includes a drive shaft  83  coupled to rotating permanent magnets  85  within bucket  60 . Permanent magnets  85  are magnetically coupled to permanent magnets  86  external to bucket  60  which, in turn, are rotatably mounted to the floor  74  ( FIG. 3 ) of jacket  70  by an axle and bearing assembly  75 . Magnets  86  are driven by a sprocket  76  coupled to a drive sprocket  78  by means of a drive belt  77 . Sprocket  78 , in turn, is driven by a vertically rotatable shaft  81  extending vertically downwardly within jacket  70  and through a flexible coupling  96  ( FIG. 3 ), which is coupled to a drive sprocket  88  rotatably mounted to the framework within cabinet  12  by suitable bearings. Sprocket  88  is coupled to a motor  90  ( FIGS. 3 and 9 ) by a second sprocket  92  and drive belt  93 . Motor  90  is controlled by bucket motor control circuit  91  ( FIG. 9 ). 
     During combustion of a specimen within combustion vessel  20  and bucket  60 , impeller  84  circulates water within the bucket  60  and around baffle  80  to uniformly and quickly reach an equilibrium so that the raise in temperature as measured by the bucket thermistor  95  ( FIG. 9 ) can be employed to determine the calorific value of the specimen being analyzed. The jacket interior  71  is supplied with circulating water through an inlet  87  and outlet  89 , shown schematically in  FIG. 9 , coupled to a circulating pump  100  and conduit  102 , which includes an electrical preheater  104  controlled to heat the water to a predetermined temperature of about 25° C. A jacket thermistor  105  is employed in connection with the control system shown in  FIGS. 10 and 11  to control the jacket temperature to the desired equilibrium temperature during an analysis. 
     As is seen in  FIG. 9 , arm  14  also optionally includes water conduits  112  and  114  for providing the same temperature water as the isothermal reservoir  71  to the bucket cover  30 . In addition to this unique isothermal equilibrium water supplying system to the bucket cover  30 , the bucket cover  30  also has other unique features now described in connection primarily with  FIGS. 5-7C . 
     Bucket cover  30  is shown in  FIGS. 5 and 6  and comprises a generally disk-shaped body having a lower slightly tapered stainless steel member  32  which includes an annular peripheral recess  34  ( FIG. 5 ) which holds an annular inflatable polymeric seal  33  which, when in the position shown in  FIG. 5 , is inflated by a pneumatic hose  31 . Hose  31  extends between a passageway  35  in coupling member  36  and a suitable nipple on inflatable seal  33 . Air for the seal is supplied through passageway which is coupled through tube  16  to a supply of air  120  ( FIG. 9 ) by means of a conduit  122  and three-way valve  121 . The selective operation of valve  121  selectively pressurizes the inflatable member seal  33  to seal the bucket cover  30  to the inner surface of the inner wall  62  of bucket  60  before, during, and after an analysis and exhausts the air to deflate seal  33  to allow the calorimeter vessel to be raised to the position shown in  FIG. 1  for removal. Cover  30  also includes an upper closure member  38  which is sealably secured to lower member  32  by suitable fastening screws in a conventional manner. The interior space between members  38  and  32  is filled with a polymeric insulation  39  to thermally isolate the interior volume  61  of bucket  60  from jacket volume  71  during an analysis. 
     As seen in  FIG. 5 , the combustion vessel  20  includes a first electrode  21  and a second electrode  22  between which there is placed a wire filament  23  to which a cotton string  23 ′ can be attached to initiate sample ignition. Vessel  20  also includes a valve  110  for the admission of the combustible oxygen via fill manifold  116  ( FIG. 9 ) prior to an analysis. Combustion vessel  20  also includes a crucible-holding arm  24  (also shown in  FIG. 6 ) for holding a crucible  37  with a specimen therein. The contact with electrode  22  is made through an insulated fitting  27  ( FIG. 5 ) in the top  25  of vessel  20  which includes a spring contact which engages an insulated electrical spring contact  29  extending through the lower member  32  of bucket cover  30 , as best seen in  FIG. 5 . The spring contact  29  is coupled to a firing circuit  107 , which has conductors  108  and  109  ( FIG. 9 ) which extend through tube  16  in insulated relationship within end fitting  36  in a conventional manner to provide a firing voltage through contact  29  to the fuse  23  through the positive conductor  22  within the combustion vessel  20 . The igniter circuit can be selectively configured for optimum current and voltage so as to provide a means to combust either a wire fuse  23  or a cotton string  23 ′ ( FIGS. 5 and 9 ). 
     The coupling of the combustion vessel  20  to bucket cover  30  assures a minimal thermal contact between the two elements during an analysis. For such purpose, the lower member  32  of cover  30  includes, as best seen in  FIGS. 7A-7C , a generally cylindrical socket  130  with a slot  132  for receiving a flanged post  140  on the cover  25  of combustion vessel  20 . Post  140  includes a cylindrical neck  142  and an enlarged head  144  which fits within slot  132  and rests upon the inwardly projecting flange  134  of socket  130 . Thus, the combustion vessel  20  hangs from the lower member  32  of bucket cover  30  through this detachable interconnection. To assure the interconnection remains in place during the movement of combustion vessel  20  into and out of bucket  60  and during an analysis, the socket  130  includes a spring-loaded keeper ball  136  which presses against the top surface of flange  144  to urge flange  144  into engagement with inwardly projecting flange  134  on socket  130 .  FIG. 7C  shows the combustion vessel  20  decoupled from mounting socket  130  in cover assembly  30 , while  FIGS. 7A and 7B  show the detail of the interconnection once the combustion vessel  20  has been mounted to the bucket cover  30 . This socket and post interconnection minimizes the thermal contact between bucket cover  30  and combustion vessel  20  to provide better thermal isolation and more accurate analysis of the temperature rise of water within the inner volume  61  of bucket  60  during and analysis. 
     Cover  25  of combustion vessel  20  is conventionally retained by a closure ring  26  threaded either by threads or by a bayonet-thread arrangement to body  28  of the vessel. Cover  25  includes a pressure-actuated valve  110  ( FIG. 5 ) which, as seen in  FIG. 9 , is employed in connection with an oxygen fill assembly including a pressurized source of oxygen  112  of approximately 450 pounds/square inch coupled through an oxygen manifold  114  to the fill manifold  116  which couples to valve  110  for filling the vessel once a sample in a crucible has been mounted within crucible-holding arm  24  and the fuse  23  positioned between electrodes  21  and  22 . The filling of the vessel using elements  112 - 116  is substantially conventional and is employed for filling the vessel  20  prior to an analysis. Subsequent to an analysis, the gas pressure inside the vessel is released by manually depressing valve  110 . 
     The isothermal jacket volume  71  is initially filled from a source of water through a manifold assembly  126  ( FIG. 9 ), which receives water at a temperature of approximately 15° C. controlled from a supply of water  127  with an external chiller  128  in the event the water temperature is too high. The manifold assembly  126  is coupled to a check valve  129  to the pump  100  which serves to fill the jacket  70  and circulate water through the jacket. Jacket  70  includes an overflow discharge  78  which is coupled to the input  79  of the external chiller  128  in a recirculation loop as seen in  FIG. 9 . Bucket cover  30  and the vessel  20  coupled thereto is moved between a raised position shown in  FIGS. 1 and 2  to a lowered operating position for an analysis, as shown in  FIGS. 3 and 5 , by drive motor  48  shown in  FIGS. 4 and 9 . The interconnection of the movable post  40  to fixed stanchion  50  to achieve this motion is now described in connection with  FIGS. 8A-8C . 
     Drive motor  48  is actuated by a motor control  47  ( FIG. 9 ). The motor  48 , as shown in  FIG. 4 , drives the threaded jack screw  44  coupled to the thrust nut  46 , which raises the bracket  42  fixed to movable post  40 . Post  40  is coupled to the stanchion  50  by means of channel  52  within stanchion  50  which receives the configured side extensions  41  of post  40  in smoothly movable relationship. Side rollers  54  are vertically spaced along both sides of extensions  41  and ride within channel  45  defined therebetween. Front and rear rollers  56  provide stability in the fore and aft direction for post  40 . The thrust nut  46  is mounted to a plate  49  which engages the lower surface of bracket  42  and, as screw jack  44  is rotated in a first direction, plate  49  raises, thereby lifting bracket  42  and post  40  attached thereto to the fully raised position shown in  FIGS. 1 and 4 . A shaft encoder  51  ( FIG. 4 ) is coupled to circuit  47  and determines the number of revolutions of jack screw  44  and thereby provides the system information as to the vertical position of combustion vessel  20  during its movement between the raised position, a substantially submerged position (not shown), and the fully submerged position ( FIGS. 3 and 5 ). 
     There is no locked mechanical connection between plate  49  and bracket  42  other than the physical contact as plate  49  is raised by thrust nut  46 . When the arm  14  holding vessel  20  and attached to post  40  is lowered by reversing the direction of the jack screw  44 , a flange  43  on bracket  42  rests upon the upper surface of plate  49  and follows plate  49  as it is lowered. As long as plates  49  and flange  43  are in contact, a spring-loaded pawl  143 , which is mounted to bracket  42 , is in a non-locking position with respect to a geared, toothed rack  146 . Pawl  143  is pivotally mounted by a pin  141  to bracket  42  and has a locking end  148  which engages notches  147  in rack  146  in the event flange  43  and plate  49  become separated. If post  40  smoothly follows the lowering of plate  49 , pawl  143  is held in a non-locked position by the contact of plate  49  and flange  43  against pawl  143  compressing spring  145 . If these plates become separated as shown in  FIG. 8C , spring  145  rotates the locking end  148  of pawl  143  which engages the rack  146 , thereby holding the arm  14  and combustion vessel  20  in a fixed vertical position until the operator can manually lower the arm  14  by releasing pawl  143  against the spring bias  145  while holding the arm against rapid acceleration downwardly. This interconnection between the jack screw  44  and post  40  allows for relatively quiet operation of the raising and lowering of combustion vessel  20  and provides a safety feature preventing inadvertent rapid lowering of the combustion vessel. 
     The sequence of operation of a cycle of an analysis is shown in connection with the flow diagram of  FIG. 10  in which the various motors and temperature sensors shown in  FIG. 9  are employed in connection with the microcontroller  152  contained on the control board  150  ( FIG. 11 ). As seen in  FIG. 10 , the sequence of an analysis is initiated by the actuation of the start switch  171  ( FIGS. 9 and 10 ) in which position of motor  48  as determined by the shaft encoder  51  is detected. If the combustion vessel and arm  14  are not in the raised open position as shown in  FIGS. 1 and 2  as indicated by test  172 , the microcontroller  152  actuates motor  48 , as indicated by block  174 , to the raised open position. At that time, the precharged and loaded combustion vessel  20  is attached to socket  130  of lower member  32  of bucket cover  30  by means of post  140 , as illustrated in  FIGS. 7A-7C  and lower the combustion vessel so as to equilibrate thermally with the jacket water, as partially shown by block  176 . Switch  171  is then again actuated to begin the analysis sequence, as shown by block  178 . The microcontroller tests the fuse  23  ( FIG. 5 ) for continuity, as indicated by block  180  and tests the pneumatic pressure from source  120 , as shown by block  182 . Next, as indicated by block  184 , motor  90  is actuated to increase the stirring rate of impeller  84  through the drive shaft  81  and the temperature of water in the jacket volume  71  is measured by thermistor  105  ( FIG. 9 ) to determine if the isothermal reservoir defined thereby has reached an equilibrium temperature of about 25° C. As it approaches the equilibrium temperature, the stirring rate is decreased, as indicated by block  188 , and motor  48  is actuated to lower combustion vessel  20  into the bucket  60 , as indicated by block  190 . Next, the inflatable seal  133  ( FIGS. 5 and 9 ) is inflated by the actuation of valve  121  to seal the bucket  60  from the surrounding reservoir  71 , as indicated by block  192 . 
     A timer delays firing, as indicated by block  194 , until equilibrium temperature has been reached upon sealing of the bucket and, as indicated by block  196 , the fuse is then fired to combust the oxygen within vessel  20  and the sample contained by the crucible contained therein. The temperature signals from thermistor  95  are then monitored, as indicated by blocks  198  and  200 , utilizing a standard thermographic methodology to determine the calorific value of the combusted sample due to the increase in water temperature upon combustion of the sample. Subsequently, seal  33  is deflated by the opening of three-way valve  121  and motor  48  is actuated to raise the combustion vessel from the bucket  60 , as indicated by block  202 . The stirring rate is then increased, as indicated by block  204  through motor  90  to again equilibrate the overall isothermal reservoir  71  with the now increased bucket water temperature in preparation for subsequent analysis. As necessary, cold water from the external chiller  128  is allowed to flow into the jacket so as to refill and cool the jacket water. 
     As indicated by block  206 , the vessel  20  is then detached, vented, cleaned, drained, rinsed, and the rate of stirrer  85  is decreased, as indicated by block  208 , as equilibrium temperature is reached between the water in bucket  60  and jacket volume  71 . If additional samples are to be run, as indicated by test  210 , the procedure beginning at block  170  is repeated. If not, as indicated by block  212 , the jacket temperature can be reduced to a standby mode, as indicated by block  214 , to disable the pump  100 , the stirrer  90 , the jacket temperature control  104 , and the bucket cover  30  is lowered to enclose the calorimeter in a position indicated in  FIG. 5  without the addition of the combustion vessel  20 . A new analysis can begin at a later time, as indicated in block  216 , by actuation of switch  171  ( FIG. 9 ), which initiates the control  104 , as indicated by block  218 . As indicated by block  220 , cover  30  is moved to an open position for access for mounting a combustion vessel  20  thereto. Then, the test for block  210  is run to determine whether or not the sequence returns to block  170  for operation of the calorimeter. 
     The control elements are shown in  FIG. 11  coupled to the microcontroller  152  by an interface circuit  154 , with the microcontroller  152  being coupled to the personal computer  160  by means of Ethernet interface  156 . Computer  160  conventionally includes a monitor  162  which displays the sequence of operation corresponding to the steps shown in the diagram of  FIG. 10  and is also coupled to a printer  164  such that a printout of the results of an analysis can be obtained. 
     Thus with the calorimeter of this invention, improved thermal isolation between the calorimeter bucket and its surrounding components is provided. Also the sealing of the bucket cover to the bucket is improved as is its coupling to the combustion vessel. A quiet and reliable and yet inexpensive drive system is provided for raising and lowering the combustion vessel into the bucket is also provided. 
     It will become apparent to those skilled in the art that various modifications to the preferred embodiments of the invention as described herein can be made without departing from the spirit or scope of the invention as defined by the appended claims.