BACKGROUND 
     The invention relates to a rotary evaporator having a distilling flask, receiving a distillate and supported rotationally around an axis, which comprises a vapor tube encompassing the axis, a cooler comprising a cooling spiral receiving a coolant and connected to a cooling circuit to form a flow path, and a distillate flask to receive the distillate, with the vapor tube connecting the distilling flask to the cooler and the distillate flask, the distilling flask being heated by a heater, the distilling flask being rotational around the axis by a drive during the heating process, and the vapor guided through the vapor tube and condensed at the cooling spiral can be collected in the distillate flask. 
     The invention further relates to a method for evaporating a material to be distilled matter, with the material to be distilled being evaporated at least partially by being inserted into a distilling flask that receives the material to be distilled that is supported rotationally around an axis, with the distilling flask with the material to be distilled being heated by a heater, with the distilling flask being rotated around the axis during the heating process by a drive, with the vapor formed due to heating being guided via a vapor tube encompassing the axis into a cooler, with said cooler comprising a cooling spiral, which is connected to a coolant circuit in order to form a flow path for a coolant, and with a coolant flowing through it, and the vapor condensing at the cooling spiral being collected in a distillate flask. 
     Such rotary evaporators and methods for evaporating a material to be distilled are known, for example from the professional article M. T. Kramer:  A Rotary Evaporator System And Its Potentials , G-I-T-Fachz. Lab., 18 th  Volume, September 1974, page 862ff, and have been largely proven in practice. A feature of the rotary evaporator particularly to be emphasized comprises that by the rotation of the distilling flask during the heating process, the material to be distilled is heated more evenly compared to conventional methods, particularly by a wide-range precipitation of the interior wall of the distilling flask with the material to be distilled. Thus, such rotary evaporators serve very well in lab technology. 
     From WO 96/05901 a method is known for regulating and controlling a distillation or condensing apparatus comprising a boiler, a heat source, and a cooler, with the cooling water circulating through the cooler accepting its temperature in the circuit and when it reaches an upper temperature limit, it is replaced by adding cold water until a lower temperature limit is reached. Here, a defined cut-off can be set if, in spite of inserting cold water, any reduction of the temperature of the cooling water fails to occur. 
     SUMMARY 
     The invention is based on the object of providing a rotary evaporator and a method for evaporating a material to be distilled suitable for the use in an automated operation. 
     In order to attain this object, in a rotary evaporator of the type mentioned at the outset it is provided that a first temperature sensor is arranged at a first position in the flow path of the coolant and a second temperature sensor is arranged at a second position in the flow path, with the first position being spaced apart from the second position by a section of the flow path of the coolant, and that means are provided to determine the flow rate of the coolant through the section. This way, information can be gathered about the present cooling performance of the cooler, which can be used for various processing steps of an automated operation. 
     The section comprises at least a portion of the section in the flow path of the coolant, in which the coolant accepts the condensation heat emitted during the condensation of the vapor. The section of the flow path can therefore form a real partial section of the cooling spiral. In this case, the temperature sensors are arranged in the cooling spiral inside the cooler. 
     It is particularly beneficial if the section is selected as large as possible, and particularly comprises the cooling spiral. This way it is achieved that the influence of the measurement inaccuracies during the temperature measurement are kept small compared to the temperature differences measured between the temperature sensors. 
     For a determination of the temperature of the coolant entering the cooler as precise as possible it may be provided that the first temperature sensor is arranged at the inlet of the cooling spiral into the cooler. The temperature sensor is therefore arranged in the area of the inlet of the coolant line of the cooling circuit into the cooler, forming the flow path, with the position of the temperature sensor being selected such that any falsification of the temperature measurement due to environmental influences is avoided, for example by heating or cooling of a part of the coolant line between the cooling spiral and the temperature sensor due to environmental influences. 
     Additionally, it may be provided that the second temperature sensor is arranged at the outlet of the cooling spiral out of the cooler. Here, too, the arrangement of the temperature sensor is selected in the flow path such that any change in temperature of the coolant after having left the cooling spiral and prior to reaching the temperature sensor is practically excluded. This may also be achieved by suitable heat insulation of the pipes of the cooling spiral in these sections. 
     For any statement concerning the cooling performance it is necessary to know the amount of coolant transported through the cooler per time unit. The determination of the flow rate of the coolant can occur, for example, by predetermining a flow rate, for example by predetermining a pressure in the cooling circuit and limiting the flow rate in the flow path, or by measuring the actual flow rate. An embodiment in which the actual flow rate can be measured may provide that the means for determining the flow rate of the coolant through the section of the flow path of the coolant comprises a flow meter. 
     Here, it is particularly beneficial when the flow meter in the flow path of the coolant is arranged outside the temperature measurement section of the flow path of the coolant. This way, any falsification of the measured temperature difference is avoided in reference to the actual temperature change caused by the cooling in the cooling spiral and/or the section due to the flow meter, particularly its heat radiation and head emissions, or by a heating of the coolant in the flow meter. It is further advantageous that the flow meter remains more easily accessible in an arrangement outside the section, for example for maintenance or control measures. 
     Particularly beneficial conditions develop during the evaporation of the product to be distilled if the cooler is connected to a vacuum generator. 
     An embodiment of the invention may provide that means for the determination and/or detection of the temporal progression of the temperature difference between the first and the second temperature sensor and the temporal progression of the flow rate is embodied. Here, it is advantageous that information concerning the changes of the operating state or the features of the material to be distilled can be yielded and used for an automated operation. 
     For example, it may be provided that means are embodied for the calculation of the distillate collected in the distillate flask within a certain period of time from the temporal progression of the determined temperature difference and from the temporal progression of the flow rate of the coolant through the section of the flow path of the coolant. This way, the rotary evaporator can be operated for example in an automated fashion until a predetermined amount of distillate has been obtained. 
     For an embodiment of the rotary evaporator to process various materials to be distilled it may be provided that means are provided to input and/or save and/or select product-specific information of the material to be distilled and/or the distillate and/or the coolant. Preferably such material-specific data is at least provided by statements concerning the specific thermal capacity of the coolant and/or the distillate, the condensation enthalpy of the distillate, and/or the effectiveness of the transfer of condensation heat into heating of the coolant. From this data the amount of heat can be determined that is fed to the coolant in the cooling circuit per time unit which is equivalent to the heat released during the condensation of the vapor into distillate. Here, the amount of heat results from the amount of coolant, its temperature change, and its specific heat capacity, based on known laws of physics. 
     It has shown that in the area of the operating temperature of the coolant its heat capacity can be changed only slightly. In this case, the temperature of the coolant is not included in the calculation but it can be assumed to be constant. Thus, an advantageous embodiment provides that only the difference between the temperatures at the first and the second temperature sensor is determined. 
     In order to perform automated processing at the rotary evaporator, a control unit can be provided, by which a control signal can be deduced for the rotary evaporator from the temporal progression of the temperature difference between the first and the second temperature sensors and the temporal progression of the determined flow rate. This way, the information about the operating status and/or process progression yielded during the operation of the rotary evaporator can be used for an automatic control by evaluating and utilizing the control signals generated by the control. 
     According to one embodiment of the invention it may be provided that means are embodied for monitoring the temporal progression of the determined temperature difference for temporal changes, particularly computing means, and that using said means information can be gathered from the temporal progression of the determined temperature difference and the temporal progression of the determined flow rate concerning the beginning and/or the end of the evaporation of a component of the distillation matter, with the control signal being able to output this information and/or the change of the heating performance of the heater and/or the pressure in the system. Here, it is advantageous that changes in the operation of the rotary evaporator can be detected. For example, the temperature difference may drop to zero at the end points of the cooling spiral or the section when the component of the material to be distilled located in the distilling flask has evaporated entirely or when the material to be distilled remaining in the distilling flask forms an azeotropic, with its evaporation temperature being altered in reference to the evaporation temperature of the components. This way, the shut-off may be triggered for the heater or the rotary evaporator and/or a change of the pressure may be caused in the system via the control signal. 
     In order to attain this object in a method of the type mentioned at the outset, it is provided that the difference of the temperatures of the coolant between two points in the flow path of the coolant, which are spaced apart from each other by a section of the flow path of the coolant is determined continuously or at regular intervals and that the flow rate of the coolant through the cooling spiral is continuously determined or at regular intervals. The intervals of the repeated determination and/or detection may be predetermined, for example, by the clock frequency of a processing unit. 
     According to one embodiment of the invention it may be provided that a control signal can be deduced for the rotary evaporator from the temporal progression of the determined temperature difference and the temporal progression of the flow rate determined. Here it is advantageous that information concerning the progression of the evaporation process and/or changes in the evaporation process can be determined and utilized. 
     A determination of the amount of heat accepted by the coolant as precise as possible is achieved if the cooling circuit from its input into the cooler to its outlet out of the cooler is selected as the section for the cooling spiral. 
     In order to support the evaporation it may be provided that during the heating process the cooler is impinged with a vacuum, particularly via a vacuum generator. A vacuum pump may be used as a vacuum generator, for example. 
     For an automated execution of the method it may be provided that the control signal influences at least one operating parameter of the rotary evaporator, particularly the heating performance and/or heater temperature of the heater, the pressure in the system of the rotary evaporator and/or the flow rate of the coolant. Here, it is advantageous that the method can be performed automatically with beneficial, particularly optimized operating parameters, and the operating parameters may be subsequently adjusted in an automated fashion during the progression of the method. 
     According to one embodiment of the invention it may be provided that the amount distilled and collected in the distillate flask is determined from the temporal progression of the determined temperature difference and the temporal progression of the determined flow rate and that the control signal causes the output of the determined value for the distilled amount. 
     An advantageous embodiment of the invention may provide that information is gathered from the temporal progression of the determined temperature difference and the temporal progression of the determined flow rate concerning the beginning and/or the end of the evaporation of a component of the material to be distilled, with the control signal causing the output of this information and/or the change of the heating performance of the heater and/or the pressure in the system. The invention uses the knowledge that no condensation occurs in the cooler prior to the beginning and after the end of the evaporation and thus the temperature difference at the cooling spiral is equal to zero or almost zero. Here, it is also advantageous that the rotary evaporator during operation can be protected from destruction or damage, for example during the heating of the material to be distilled due to the complete consumption of the available component of the material to be distilled provided for evaporation. Accordingly, the beginning of boiling or evaporation of unknown samples can be also determined, in particular. 
     Additionally, changes of the material mixture used as material to be distilled during the distillation i.e. during evaporation can be determined because these changes lead to changes in the boiling temperature and/or in the condensation energy, by which the determined temperature difference changes. This change can be evaluated and used for generating a control signal to exchange the distillate flask and/or to cancel the distillation. 
     In order to reach short operating times until the predetermined amount of distillate is yielded it may be provided that information is gathered from the temporal progression of the determined temperature difference and the temporal progression of the determined flow rate concerning the utilization of the cooler, with the control signal causing the output of said information and/or the control signal regulating the operating parameters of the rotary evaporator, particularly the heating performance of the heater, the pressure in the system of the rotary evaporator, and/or the flow rate of the coolant such that the utilization of the cooler is optimized, particularly that it amounts to a predetermined value and/or that the vapor is kept from reaching the vacuum generator. With the control of the temperature difference between the first and the second position in the flow path of the coolant via the pressure in the cooler and/or the temperature in the heater the distillation speed can be adjusted to the maximally possible cooling performance of the cooler, particularly in case of a predetermined flow rate of coolant. This way, a temporal optimization of the distillation is possible depending on the available cooling performance. 
     In one embodiment according to the invention it may be provided that during the determination of the distilled amount collected in the distillate flask the specific heat capacity of the coolant and/or the distillate, the condensation enthalpy of the distillate, and/or the effectiveness of the conversion of the condensation heat into the heating of the coolant can be considered. The method can therefore be adjusted and used for a multitude of various distillation matters and/or for a multitude of various distillation processes. Thus, a control of the distillation amount can be implemented. Due to the fact that the specific heat capacity of the coolant in the operating areas of the cooler are only slightly temperature dependent it may be considered to be constant. Temperature variations in the coolant at the inlet into the cooler have only minor effects. 
     A particularly simple embodiment of the method, which already shows satisfactory results for many applications, may provide that the control signal is determined from the difference of the determined temperature difference and a target temperature difference. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The invention is now described in greater detail using an exemplary embodiment; however, it is not limited thereto. Additional exemplary embodiments are discernible for one trained in the art by combining the features of the exemplary embodiment with each other or with features of the claims. 
         FIG. 1  shows a sketch illustrating the principle of a rotary evaporator according to the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A rotary evaporator, marked  1  in its entirety, has a distilling flask  4  supported rotationally around an axis  2 . The distilling flask receives a material to be distilled  3 . 
     A vapor tube  5  is connected to the distilling flask  4  and thus connected to its interior. This vapor tube  5  is aligned such that it encompasses the axis  2  and thus is safe from hindering the rotary motion of the distilling flask  4 . 
     The rotary evaporator  1  further comprises a cooler  6 . The vapor tube  5  opens at the lower end  24  of the cooler  6  in the interior chamber of the cooler  6 . A cooling spiral  8  is arranged in said interior chamber. The cooling spiral  8  is connected to the cooling circuit, not shown in greater detail, in order to form a flow path  7 . The flow path  7  is filled with a coolant, which during operation flows along the flow path  7  in order to perform cooling. 
     In order to collect the distillate  10 , the rotary evaporator  1  has a distillate flask  9 . The vapor tube  5  opens in a T-shaped fashion in a connection tube  22  between the interior chamber of the cooler  6  and the interior of the distillate flask  9 , by which the vapor tube  5  connects the distillation flask  4  to the cooler  6  and the distillate flask  9 . 
     The distillation flask  4  can be heated by a heater  11 . The heater  11  is embodied in a known fashion and heats the distillation flask  4  via a water bath. 
     During the heating process the distillation flask  4  is rotated by a drive  12  around the axis  2 . 
     The vapor  13  created by heating the material to be distilled  3  can therefore be guided through the vapor tube  5  and condensed at the cooling spiral  8 . The distillate flask  9  is arranged in a known fashion such that it can collect the condensed vapor  13  in the distillate flask  9 . 
     In order to determine the heating of the coolant in the cooling spiral a first temperature sensor  15  is arranged at a first position  14  in the flow path  7  of the coolant and a second temperature sensor  17  is arranged at a second position  16  in the flow path  7  of the coolant. The first location  14  is here spaced apart from the second position  16  by a section  18  of the flow path  7  of the coolant. 
     Means  19  are provided to determine the flow rate of the coolant through the section  18 . 
     In the described exemplary embodiment the first temperature sensor  15  is arranged at the cooling spiral  8  in the cooler  6 . The second temperature sensor  17  is arranged at the outlet  16  of the cooling spiral  8  from the cooler  6 . The positions of the temperature sensors are selected such that the determined temperatures correctly reflect the heating of the coolant by the condensation of the vapor  13  to the extent possible without being falsified by any influence of the environment upon the temperature of the coolant. 
     A flow meter  19  is arranged in the flow path  7  in order to determine the flow rate of the coolant through the section  18  of the cooling medium flow path  7 . In the exemplary embodiment, the flow meter  19  has an impeller driven by the flowing coolant and this way reflecting the flow rate. 
     The flow meter  19  is arranged in the flow path  7  of the coolant outside the section  18  of the flow path  7  of the coolant. 
     The cooler  6  is connected at its head  23  via a connection tube  21  to a vacuum generator  20 . The vacuum generator  20  impinges the interior chamber of the cooler  6  with a vacuum. 
     Means not shown in greater detail to determine and/or detect the temporal progression of the temperature difference between the first  15  and the second  17  temperature sensor and the temporal progression of the flow rate are embodied at the rotary evaporator  1 . These means also comprise storage means or a memory, in which the determined and/or detected temporal progressions can be saved. 
     Further, means not shown in greater detail are also embodied to calculate the distillate  10  collected in the distillate flask  9  within a period from the temporal progression of the determined temperature difference and from the temporal progression of the flow rate of the coolant through the section  18  of the flow path  7  of the coolant. 
     For this purpose, the rotary evaporator  1  comprises additional means, not shown, to input and/or store and/or select material-specific data of the material to be distilled  3  and/or the distillate  10  and/or the coolant. In particular, the specific heat capacity of the coolant and the distillate  10 , the condensation enthalpy of the distillate  10  can be predetermined and the effectiveness of the conversion of the condensation heat into the heating of the coolant can be stored. 
     For an automatic regulation of the evaporation process the rotary evaporator  1  comprises a control unit, by which a control signal can be deduced for the rotary evaporator  1  from the temporal progression of the temperature difference between the first  15  and the second  17  temperature signal. For this purpose, the temporal progression of the flow rate determined can be considered. 
     A controller is embodied at the rotary evaporator  1  to monitor the temporal progression of the determined temperature difference for temporal changes. Using this means, information can be gathered from the temporal progression of the determined temperature difference and, if applicable, the temporal progression of the determined flow rate concerning the beginning and/or the end of the evaporation of a component of the distillation matter  3 . A control signal then causes the output of said information and a change of the heating performance of the heater  11  and/or the pressure in the system. 
     Using the rotary evaporator  1  a method can be performed to evaporate a material to be distilled, which is explained in greater detail in the following. 
     The material to be distilled  3  by at least partial evaporation is inserted into the distillation flask  4 . The distillation flask  4  is supported rotationally around the axis  2  and embodied to collect the distillation matter  3 . Subsequently the distillation flask  4  with the material to be distilled  3  is heated via the heater  11 . For this purpose, the distillation flask  4  is partially immersed in the water bath of the heater  11 . The heater  11  heats the water of the water bath and regulates its temperature to a predetermined value, at which a component of the material to be distilled  3  evaporates. 
     During the heating process the distillation flask  4  is rotated around the electrically driven drive  12  around the axis  2 , in order to achieve an even and rapid heating. The vapor  13  forming by way of heating is guided via the vapor tube  5  encompassing the axis  2  into the cooler  6 . Instead of the vapor  13 , the term steam is also common. 
     The cooler  6  comprises in its interior chamber a cooling spiral  8 . The cooling spiral  8  is connected to a coolant circuit. This way, a cooling path  7  is formed for the coolant, in which coolant flows through the cooling spiral  8 . 
     The vapor  13  condensed at the cooling spiral  8  is collected in the distillate flask  9 . 
     During the process the difference of the temperatures of the coolant is continuously or in repeated intervals determined between two locations  14 ,  16  in the flow path  7  of the coolant, distanced from each other by the section  18  of the flow path  7  of the coolant, and the flow rate of the coolant is determined from said section  18  on a continuous basis or in repeated intervals. The cooling spiral  8 , from its inlet  14  into the cooler  6  to its outlet  16  out of the cooler  6 , is selected as the section  18  of the coolant circuit. 
     During the heating process, the cooler  6  and the entire distillation system is impinged with a vacuum from the vacuum generator  20 . 
     A control signal is deduced for the rotary evaporator  1  from the temporal progression of the determined temperature difference and the temporal progression of the determined flow rate. Said control signal comprises several information units and is transferred as a multi-component signal serially via at least one communications channel or parallel via several communications channels. 
     This control signal influences an operating parameter of the rotary evaporator  1 , for example the heating power of the heater  11 , the pressure in the cooler  6 , and/or the flow rate of the coolant. 
     The distilled amount, collected in the distillate flask  9 , is determined from the temporal progression of the determined temperature difference and the temporal progression of the determined flow rate. The control signal results in an output of the determined value for the distilled amount. 
     Further, information is gathered concerning the beginning and/or the end of the evaporation of a component of the material to be distilled  3  from the temporal progression of the determined temperature difference and the temporal progression of the determined flow rate. The control signal causes the output of said information on a display. The control signal also causes the change of the heating power of the heater  11 . This way, the heating power, particularly the operating temperature of the water bath or the heater  11  and/or the pressure in the system are adjusted to the evaporating temperature of the component to be evaporated. 
     Information is gathered from the temporal progression of the determined temperature difference and the temporal progression of the determined flow rate about the utilization of the cooler  6 . The control signal causes the output of said information. The control signal controls the operating parameters of the rotary evaporator  1 , particularly the heating power of the heater  11 , the pressure in the system of the rotary evaporator  1 , and/or the flow rate of the coolant such that the utilization of the cooler  6  is optimized. Here, the temperature difference at the cooling spiral  8  is monitored and the operating parameters are modified such that vapors are condensed only over a length of approximately 80%, i.e. from 70% to 90% or from 75% to 85% or precisely 80% of the length of the cooling spiral  8 , measured prior to entering the cooler  6 . The temperature difference equivalent to this utilization of the cooler  6  is determined for the rotary evaporator  1  prior to operation by way of experiments and stored in the control. These tests occur by varying the operating parameters under the visual control of the condensation processes at the cooling spiral  8 , particularly the size of the section of the cooling spiral  8 , at which vapor  13  condenses. By the adjustment to the predetermined value it is achieved that the vapor  13  is prevented from entering the vacuum generator  20 . It is known that above a certain temperature difference at the cooling spiral  8 , depending on operating parameters of the rotary evaporator  1 , particularly the cooler  6 , a quantitative condensation of the distillate  10  is no longer possible. When the cooler  6  is overstrained in its performance in this way, vapor  13  exits the cooler  6  and is lost from the process. 
     When determining the amount of matter distilled and collected in the distillate flask  9  the specific heat capacity of the coolant and the distillate  10 , the condensation enthalpy of the distillate  10 , and the effectiveness of the conversion of the condensation heat into heating the coolant are considered. From the temperature difference determined at the cooling spiral  8  and using the knowledge of the flow rate through the cooling spiral  8  the heat amount accepted by the coolant per time unit is determined. This is equivalent to the heat amount emitted during condensation of the vapor  13 . This way, the amount of condensed distillate  10  can be calculated from the condensation enthalpy of the distillate  10  and the calculated heat amount. For many materials, instead of the exact specific values, preset standard values may also be used. 
     The control and monitoring of the utilization of the cooler  8  calculates the difference Z=X−Y of the determined temperature difference X at the cooling spiral  8  and a target-temperature difference Y and uses Z as the variable. 
     At the starting point of the distillation the actual value X of the temperature difference at the cooling spiral  8  is almost zero because no vapor  13  condenses at the cooling spiral  8 . Now, a target value Y is selected for the temperature difference. The heating power in the heater  11  and/or the pressure in the system is adjusted to the predetermined target-temperature difference Y. This way, the desired amount of distillate is produced. 
     In the rotary evaporator  1  with a cooler  6 , temperature sensors  15 ,  17  are arranged in the inlet  14  and the outlet  16  of the coolant into and/or out of the cooler  6 , and the flow rate of the coolant through the cooler  6  is determined. The beginning and/or the end of the condensation in the cooler  6  is deduced from the increase and/or reduction of the difference of the temperatures X at the temperature sensors  15 ,  17 . The amount of the condensed distillate  10  is determined from the difference of the temperatures X and a control of the distillation amount is performed. The utilization of the cooler  6  is controlled by controlling the heating power of the heater  11  and/or the pressure in the system depending on the difference of the temperatures X.
A rotary evaporator ( 1) having a cooler ( 6), wherein temperature sensors ( 15, 17) are disposed in the inlet ( 14) and outlet ( 16) of the coolant into or out of the cooler ( 6), and a volume flow rate of the coolant through the cooler ( 6) is determined. The initiation or termination of condensation in the cooler ( 6) is derived from an increase or decrease in the difference of the temperatures (X) at the temperature sensors ( 15, 17). The volume of the condensed distillate ( 10) is determined from the difference in temperatures (X), and a distillation volume control is performed. By regulating the heating power of the heater ( 11) and/or the pressure in the system, the loading of the cooler ( 6) is controlled as a function of the difference in temperatures (X).