302 METHODS OF ANALYSIS [Chap. 



200 mg. When solid remove the disk and allow to stand 2-3 hours in order to obtain 

 the normal melting point. 



Place a test tube, 30 by 3.5 cm., containing the alcohol-water mixture, in a tall 

 beaker, 35 by 10 cm., containing ice and water, until cold. Then drop the disk of 

 fat into the tube and it will at once sink to a point where the density of the alcohol- 

 water mixture is exactly equivalent to its own. Lower an accurate thermometer, 

 which can be read to 0.1°C., into the test tube until the bulb is just above the disk. 

 In order to secure an even temperature in all parts of the alcohol-water mixture 

 around the disk, stir gently with the thermometer. Slowly heat the water in the 

 beaker, constantly stirring it by means of an air blast or other suitable device. 



When the temperature of the alcohol-water mixture rises to about 6°C. below 

 the melting point of the fat, the disk of fat begins to shrivel and gradually rolls up 

 into an irregular mass. Lower the thermometer until the fat particle is even with 

 the center of the bulb. Rotate the thermometer bulb gently and regulate the 

 temperature so that about 10 minutes for the increment of the last 2°C. are 

 required. As soon as the fat mass becomes spherical, read the thermometer. 

 Remove the tube from the bath and again cool. Place in the bath a second tube 

 containing the alcohol-water mixture. The test tube is of sufficiently low tempera- 

 ture to cool the bath to the desired point, ice water having been used for cooling. 

 After the first or preliminary determination, regulate the temperature of the bath 

 so as to reach a maximum of about 1.5°C. above the melting point of the fat under 

 examination. 



Do not allow the edge of the disk to touch the sides of the tube. If so, make a 

 new determination. Run triplicate determinations of which the second and third 

 results should agree closely. 



1 1 Capillary Tube Method^. — Tentative. 



Draw the melted fat or fatty acids into a thin-walled capillary tube. Use a 

 column of fat 1-2 cm. long, according to the length of the thermometer bulb. Seal 

 1 end of the tube and cool on ice 12-15 hours. Attach the capillary tube to the bulb 

 of an accurate thermometer, graduated to 0.2°C., immerse in a large test tube of 

 water surrounded by a beaker of water and heat very slowly. An apparatus 

 similar to that indicated in Fig. 12 may be used. The temperature at which the 

 substance becomes transparent is taken as the melting point. 



TITER TEST. 



Alcoholic or Aqueous Sodium Hydroxid Method. — Tentative. 



12 APPARATUS. 



Standard thermometer. — The thermometer must have a zero mark, 0.1° gradua- 

 tions between 10°-60°C., and auxiliary reservoirs at the upper end and between the 

 0° and the 10° marks. The cavity in the capillary tube between the 0° and the 

 10° marks must be at least 1 cm. below the 10° mark, which must be about 3-4 cm. 

 above the bulb, the total length of the thermometer being about 38 cm. The bulb 

 should be about 3 cm. long and 6 mm. in diameter. The stem of the thermometer 

 should be 6 mm. in diameter and made of the best thermometer tubing, with scale 

 etched on the stem, the graduation to be clear cut and distinct. The thermometer 

 should have been annealed for 75 hours at 450°C., and the bulb should be of Jena 

 normal 16'" glass, moderately thin, so that the thermometer will be quick-acting. 



