The distillation flask is closed with a rubber stopper carrying a bulb-tube which ends above in a glass tube about three-quarters of a meter long, bent at an acute angle, and passing obliquely downward on a convenient support. This tube is connected by a rubber, with the end tube bent nearly at a right angle and dipping into the standardized acid in the erlenmeyer receiver. The general arrangement of the distilling apparatus is shown in figure 12. Since the contents of the vessel are warmed by mixing with the soda-lye, the flame can be turned on at full head at once at the commencement of the operation. In about a quarter of an hour the liquid in the receiver will be at the boiling-point, and the boiling should be continued for five minutes more, making twenty minutes in all for the completion of the distillation. By this boiling the contents of the receiver are not charged with carbon dioxid, as might happen if a condenser were used. The receiver contains twenty cubic centimeters of a standardized sulfuric acid solution and about fifty cubic centimeters of water. [Illustration: FIGURE 12. DISTILLATION APPARATUS OF HALLE AGRICULTURAL LABORATORY.] The acid used should contain 38.1 grams of sulfuric acid of 1.845 specific gravity in a liter; and it should be set by titration with chemically pure sodium carbonate. For this purpose seven-tenths gram of sodium carbonate is heated in a platinum crucible for two hours over a small flame, weighed, and placed in an erlenmeyer together with twenty cubic centimeters of the sulfuric acid, care being taken to avoid loss from the vigorous evolution of carbon dioxid. After boiling for ten minutes all the carbon dioxid is removed from solution. After cooling, the excess of acid is determined by titration with a standardized barium hydroxid solution, using rosolic acid as indicator. The solution of barium hydroxid is made as follows: Digest, with warm water, 260 grams of caustic baryta, Ba(OH)₂, until it is nearly all dissolved, filter, and make up to a volume of ten liters and keep in a flask free of carbon dioxid. A solution of barium hydroxid is to be preferred to the corresponding sodium compound for titration. If traces of carbonate be formed in the two liquids, the sodium salt will remain in solution while the barium compound will settle at the bottom of the flask. _The Indicator._—The indicator used to determine the end of the reaction is made by dissolving one gram of rosolic acid in fifty cubic centimeters of alcohol. From one to two drops are enough for each titration. The color reaction is less definite as the quantity of ammonia in the liquid increases. When the titration solutions have been prepared as above described it is found to require about ninety of the barium hydroxid to neutralize twenty cubic centimeters of the sulfuric acid. By direct titration with sodium carbonate it is ascertained how many grams of nitrogen the twenty cubic centimeters of sulfuric acid represent.