EDIBLE FATS AND OILS. 135 



the sides of the tube make a new trial. Make triplicate determinations; the 

 second and third results should agree closely. Prepare these disks a day, or 

 at least a few hours, before using. 



(b) MELTING POINT OF FATTY ACIDS.O PROVISIONAL. 



Draw the melted fatty acid into a very thin-walled capillary tube 1 or 2 

 inches long, according to the length of bulb of the thermometer used. Seal 

 one end of the tube and allow the fatty acid to cool on ice for from twelve 

 to fifteen hours. Attach to the bulb of a delicate thermometer graduated to 

 one-fifth degree, immerse in a beaker of water, and heat very slowly. The 

 point at which the fatty acid becomes transparent is called the melting point 



5. Titer Test. Provisional. 



(a) STANDARD THERMOMETER. 



The thermometer must be graduated in tenth degrees from 10 to 60, with 

 a zero mark, and have an auxiliary reservoir at the upper end, also one 

 between the zero mark and the 10 mark. The cavity in the capillary tube 

 between the zero mark and the 10 mark must be at least 1 cm below the 10 

 mark, the 10 mark to be about 3 or 4 cm above the bulb, the length of the 

 thermometer being about 15 inches over all. The thermometer is annealed 

 for 75 hours at 450 C., and the bulb is of Jena normal 16 l glass, moderately 

 thin, so that the thermometer will be quick acting. The bulb is about 3 cm 

 long and G mm in diameter. The stem of the thermometer is 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, but quite fine. 



(b) DETERMINATION. 



Saponify 75 grams of fat in a metal dish with 60 cc of 30 per cent sodium 

 hydroxid (3G Baum) and 75 cc of 95 per cent by volume alcohol or 120 cc 

 of water. Boil to dryness, with constant stirring to prevent scorching, over a 

 very low flame or over an iron or asbestos plate. Dissolve the dry soap in a 

 liter of boiling water, and if alcohol has been used boil for forty minutes in 

 order to remove it, adding sufficient water to replace that lost in boiling. 

 Add 100 cc of 30 per cent sulphuric acid (25 Baum6) to free the fatty acids, 

 and boil until they form a clear, transparent layer. Wash with boiling water 

 until free from sulphuric acid, collect in a small beaker, and place on the 

 steam bath until the water has settled and the fatty acids are clear; then 

 decant them into a dry beaker, filter, using hot-water funnel, and dry twenty 

 minutes at 100 C. When dried, cool the fatty acids to 15 or 20 C. above 

 the expected titer and transfer to the titer tube, which is 25 mm in diameter 

 and 100 mm in length (1 by 4 inches) and made of glass about 1 mm in thick- 

 ness. Place in a 16-ounce saltmouth bottle of clear glass, about 70 mm in 

 diameter and 150 mm high (2.8 by 6 inches), fitted with a cork, which is 

 perforated so as to hold the tube rigidly when in position. Suspend the ther- 



U. S. Dept. Agr., Division of Chemistry, Bui. 13, Part 4, p. 448 ; Benedikt and Lew- 

 kowitsch, Oils, Fats, and Waxes, p. 97 ; Wiley, Principles and Practice of Agricultural 

 Analysis, 3: 321. 



