KP X 1587 at the region of the wall in contact with the sample; insert it into cylinder A, and fix with cork stopper). 12. Determination of Specific C: A marked line. Gravity and Density D: Bath made of glass or plastics. E: Stirring rod made of glass or stainless steel (3 The density ρ (g/mL or g/cm3) means the mass per mm in diameter, the lower end part of it is bent to unit volume, and the relative density means the ratio of make a loop, about 18 mm in diameter). the mass of a sample specimen to that of an equal vol- F: Thermometer with an immersion line. ume of a standard substance. The relative density is G: Thermometer with an immersion line or a total also called the specific gravity. ′ immersion thermometer. The specific gravity, d t , means the ratio of the H: Immersion line. t mass of the sample specimen at t′ °C to that of an equal Procedure volume of water (H2O) at t °C. Unless otherwise speci- Transfer the sample into sample container B up to fied, the measurement is to be performed by Method 1, the marked line C. When the sample is solid, melt the Method 2, or Method 4. When the specified value is sample by heating to a temperature not higher than accompanied with the term “about” in the monograph, 20 °C above the expected congealing point, and trans- Method 3 is also available. fer to B. Fill the glass or plastic bath D with water at a temperature about 5 °C below the expected congealing Method 1. Measurement using a pycnometer point. When the sample is liquid at room temperature, A pycnometer is a glass vessel with a capacity of fill bath D with water at a temperature between 10 °C usually 10mL to 100mL, having a ground-glass stopper and 15 °C lower than the expected congealing point. fitted with a thermometer, and a side inlettube with a Insert the sample container B containing the sam- marked line and a ground-glass cap. ple into cylinder A. Adjust the immersion line H of Weigh a pycnometer, previously cleaned and thermometer F to the same level of the meniscus of the dried, to determine its mass, M . Remove the stopper sample. After cooling the sample to about 5 °C above and the cap. Fill the pycnometer with the test solution, the expected congealing point, move vertically the stir- keeping them at a slightly lower temperature by 1 °C to rer E at the rate of about 60 to 80 strokes per minute, 3 °C than the specified temperature t′ °C, and stopper and observe the thermometer readings at 30 second them, taking care not to leave bubbles. Raise the tem- intervals. The temperature falls gradually. Discontinue perature gradually, and when the thermometer shows stirring, when an appreciable amount of crystals has the specified temperature, remove the portion of the formed and the temperature is constant or has begun to test solution above the marked line through the side rise. Usually, read the maximum temperature (reading tube, cap the side tube, and wipe the outside surface of F), that is constant for a while after a rise of temper- thoroughly. Measure the mass M1 of the pycnometer ature. If no rise of temperature occurs, read the temper- filled with the test solution. Perform the same proce- ature that is constant for a while. The average of not dure, using the same pycnometer containing water, and less than four consecutive readings that lie within a note the mass M2 at the specified temperature t °C. The t′ range of 0.2 °C constitutes the congealing point. specific gravity dt can be calculated by use of the Note: If a state of super cooling is anticipated, rub following equation. the inner wall of bath B or put a small fragment of the solid sample into bath B for promoting the congeal- − t′ M1 M ment, when the temperature approaches near the ex- d = t M − M pected congealing point. 2 TFurther, when measurements for a test solution and water are performed at the same temperature (t °C 11. Crystallinity Test = t′ °C), the density of the test solution at the tempera- ′ ture t′ °C ( ρ t ) can be calculated from the measured Crystallinity test is a method for the measurement T t′ of the crystallinity of the sample using a phasecontrast specific gravity dt : and the density of water at the ′ microscope. temperature t′ °C ( ρ t ) indicated in the attached Table Procedure: Float the sample on a mineral oil, and S1 by using the following equation. perform the test by using an appropriate phasecontrast microscope. To small amount of the sample, add 1~2 ρ t′ = ρ t′ ⋅ t′ drops of fluid paraffin, shake and mix, and observe the T S1 dt sample under a microscope in the course of rotating 90 °. If the sample is fine powder, immersion oil meth- Method 2. Measurement using a Sprengel Ostwald od is employed. If the sample has crystallinity, bire- Pycnometer fringence and quenching phenomenon is observed. A Sprengel-Ostwald Pycnometer is a glass vessel with a capacity of usually 1mL to 10mL. As shown in the figure, both ends are thick-walled fine tubes (inside 1588 General Tests, Processes and Apparatus diameter: 1 mm ~ 1.5 mm, outside diameter: 3 mm ~ 4 Further, when measurement of the specific gravity mm), one of which, tube A, has a line C marked on it. for a test solution is performed at the same temperature Determine the mass of a pycnometer, M, previously ( t′ °C = t °C), at which the hydrometer is calibrated, cleaned and dried, by hanging it on the arm of a chemi- ρ t′ the density of a test solution at t′ °C, T , can be cal- cal balance with a platinum or aluminum wire D. Im- t′ merse the fine tube B in the test solution, which is at a culated by using the specific gravity dt and the lower temperature by 3 °C to 5 °C than the specified equation shown in Method l. temperature t′ °C. Attach rubber tubing or a ground- glass tube to the end of A, and suck up the test solution Method 4. Measurement using an oscillator-type until the meniscus is above the marked line C, taking density meter care to prevent bubble formation. Immerse the Density measurement with an oscillator-type den- pycnometer in a water bath kept at the specified tem- sity meter is a method for obtaining the density of liq- perature t′ °C for about 15 minutes, and then, by attach- uid or gas by measuring the intrinsic vibration period T ing a piece of filter paper to the end of B, adjust the (s) of a glass tube cell filled with sample specimen. level of the test solution to the marked line C. Take the When a glass tube containing a sample is vibrated, it pycnometer out of the water bath, wipe thoroughly the undergoes a vibration with an intrinsic vibration period outside surface and determine the mass M1 . By use of T in proportion to the mass of the sample specimen. If the same pycnometer, perform the same procedure for the volume of the vibrating part of the sample cell is the standard solution of water. Weigh the pycnometer fixed, the relation of the square of intrinsic oscillation containing water at the specified temperature t °C, and period and density of the sample specimen shall be t′ linear. note the mass M2 . Calculate the specific gravity d , t Before measuring a sample density, the respective according to the equation described in Method l. intrinsic oscillation periods T and T for two Further, when measurements of specific gravity S1 S 2 for a test solution and water are performed at the same reference substances (density: ρS1 , ρS2 ) must be meas- ured at a specified temperature t′ °C, and the cell con- temperature (t' °C = t °C), the density of test solution at -3 -2 temperature t′ °C can be calculated by using the equa- stant Kt′ (g ⋅cm ⋅s ) must be determined by using the tion described in Method l. following equation. ρ t′ − ρ t′ S1 S2 K ′ = t 2 − 2 TS1 TS2 Usually, water and dried air are chosen as refer- ence substances. Here the density of water at t′ °C, ρ t′ S1 , is taken from the attached Table, and that of dried ρ t′ air, S 2 , is calculated by using the following equation, where the pressure of dried air, is at pkPa. ρ t′ = × 273.15 × p S 2 0.0012932 273.15 + t′ 101.325 Next, introduce a sample specimen into a sample cell having a cell constant Kt′, the intrinsic vibration period, TT , for the sample under the same operation conditions as employed for the reference substances. Figure 1. Sprengel-Ostwald pycnometer. ′ The density of a sample specimen at t′ °C, ρ t , is cal- T Method 3. Measurement using a hydrometer culated by use of the following equation, by introduc- Clean a hydrometer with ethanol or ether. Stir the ing the intrinsic oscillation period TS1 and the density ρ t′ sample well with a glass rod, and float the hydrometer of water at a specified temperature t′ °C, S1 , into the in the well. When the temperature is adjusted to the equation. specified temperature t′ °C and the hydrometer comes ′ t ′ ′ to a standstill, read the specific gravity dt or the ρ t = ρ t + 2 − 2 T S1 K t (TT TS1 ) ρ t′ density T at the upper brim of the meniscus.