21.122—Pyridine bases.
(a) Alkalinity.
One ml of pyridine bases dissolved in 10 ml of water is titrated with 1 N H2 SO4 until a drop of the mixture placed upon Congo paper shows a distinct blue border, which soon disappears. A minimum of 9.5 ml of the acid must be required for the end point. (Congo paper: filter paper treated with 0.1 percent aqueous solution of Congo red and dried.)
(b) Distillation range.
One hundred ml of the denaturant are distilled in the following manner: The sample is placed in a short-necked glass flask of about 200 ml capacity which is rested on an asbestos plate having a circular opening of 30 mm in diameter. The neck of this flask is fitted with a fractionating tube 12 mm in diameter and 170 mm long and having a bulb just 1 cm below the side tube which is connected with a Liebig condenser having a water jacket not less than 400 mm in length. A standardized thermometer is placed in the fractionating tube so that the mercury bulb is suspended in the center of the fractionating bulb. Heat is applied slowly and in such manner that 5 ml of distillate is collected per minute in a graduated cylinder. At least 50 ml must distill at or below 140 °C. and at least 90 ml below 160 °C.
(1)
Ten ml of this solution are treated with 5 ml of 5 percent aqueous solution of anhydrous fused CaCl2 and the mixture vigorously shaken. An abundant crystalline separation should occur within 10 minutes.
(2)
Ten ml of the pyridine solution mixed with 50 ml of Nessler's reagent must give a white precipitate.
(d) Water content.
Twenty ml of pyridine bases are shaken with 20 ml of a caustic soda solution having a specific gravity of 1.40 (15.56 °/15.56 °C.) and the mixture allowed to stand until completely separated into two layers. The amount of pyridine base layer should be 18.5 ml, minimum.