á721ñDISTILLING RANGE
To determine the range of temperatures within which an official liquid distils,or the percentage of the material that distils between two specified temperatures,use Method Ior Method IIas directed in the individual monograph.The lower limitof the range is the temperature indicated by the thermometer when the first drop of condensate leaves the tip of the condenser,and the upper limitis the Dry Point,i.e.,the temperature at which the last drop of liquid evaporates from the lowest point in the distillation flask,without regard to any liquid remaining on the side of the flask,or the temperature observed when the proportion specified in the individual monograph has been collected.
NOTE—Cool all liquids that distill below 80to between 10and 15before measuring the sample to be distilled.

Method I
Apparatus— Use apparatus similar to that specified for Method II,except that the distilling flask is of 50-to 60-mLcapacity,and the neck of the flask is 10to 12cm long and 14to 16mm in internal diameter.The perforation in the upper insulating board,if one is used,should be such that when the flask is set into it,the portion of the flask below the upper surface of the insulating material has a capacity of 3to 4mL.
Procedure— Proceed as directed for Method II,but place in the flask only 25mLof the liquid to be tested.

Method II
Apparatus— Use an apparatus consisting of the following parts:
Distilling Flask— Around-bottom distilling flask,of heat-resistant glass,of 200-mLcapacity,and having a total length of 17to 19cm and an inside neck diameter of 20to 22mm.Attached about midway on the neck,approximately 12cm from the bottom of the flask,is a side-arm 10to 12cm long and 5mm in internal diameter,which forms an angle of 70to 75with the lower portion of the neck.
Condenser— Astraight glass condenser 55to 60cm in length with a water jacket about 40cm in length,or a condenser of other design having equivalent condensing capacity.The lower end of the condenser may be bent to provide a delivery tube,or it may be connected to a bent adapter that serves as a delivery tube.
Insulating Boards— Two pieces of insulating board,5to 7mm thick and 14to 16cm square,suitable for confining the heat to the lower part of the flask.Each board has a hole in its center,and the two boards differ only with respect to the diameter of the hole,i.e.,the diameters are 4and 10cm,respectively.In use,the boards are placed one upon the other,and resting on a tripod or other suitable support,with the board having the larger hole on top.
Receiver— A100-mLcylinder graduated in 1-mLsubdivisions.
Thermometer— In order to avoid the necessity for an emergent stem correction,an accurately standardized,partial-immersion thermometer having the smallest practical subdivisions (not greater than 0.2)is recommended.Suitable thermometers are available as the ASTM E-1series 37Cthrough 41C,and 102Cthrough 107C(see Thermometers á21ñ).When placed in position,the stem is located in the center of the neck and the top of the contraction chamber (or bulb,if 37Cor 38Cis used)is level with the bottom of the outlet to the side-arm.
Heat Source— Asmall Bunsen burner or an electric heater or mantle capable of adjustment comparable to that possible with a Bunsen burner.
Procedure— Assemble the apparatus,and place in the flask 100mLof the liquid to be tested,taking care not to allow any of the liquid to enter the side-arm.Insert the thermometer,shield the entire burner and flask assembly from external air currents,and apply heat,regulating it so that between 5and 10minutes elapse before the first drop of distillate falls from the condenser.Continue the distillation at a rate of 4to 5mLof distillate per minute,collecting the distillate in the receiver.Note the temperature when the first drop of distillate falls from the condenser,and again when the last drop of liquid evaporates from the bottom of the flask or when the specified percentage has distilled over.Correct the observed temperature readings for any variation in the observed ambient barometric pressure from the normal (760mm),adding if the pressure is lower or subtracting if the pressure is higher than 760mm,and apply the emergent stem correction where necessary.Unless otherwise specified in the individual monograph,allow 0.1for each 2.7mm (0.037per mm)of variation.