Semimicro- and Micro-Kjeldahl
Steam-Distillation Unit J. €1. BRANT AND D. C. SIEVERS, Tennessee Eastman Corporation, Kingsport, Tenn.
T
HE steam-distillation of liberated ammonia in the Kjel-
TABLE I. DETERMISATIOS OF NITROGEN
dah1 nitrogen determination has been the subject of considerable study. T h e well-known apparatus of Parnas and Wagner, utilized by Pregl (6), is familiar t o those concerned with microanalyses. Its chief difficulties lie in its bulkiness and the necessity for a n elaborately constructed vacuum-insulated distilling chamber.
Time of Distilla- Sitrogen tion Found Min. Mg. 10
This latter fault has been eliminated in various ways. Kemmerer and Hallett (4) used a n improved steam-generating unit, which was only a slight improvement over the original apparatus. Fife (8) laced a steam chamber between the steam generator and the distikng chamber. Allen (1) clamped his digestion flask to a steam generator. Redemann (7) modified Allen's design and adapted it to the semimicrodetermination. The one-piece, allglass apparatus of Kirk (6) was a vast improvement in design. I n place of a vacuum-insulated distilling chamber, he used a steam-jacketed chamber, the steam from which entered the distilling chamber and effected the distillation.
4
Av.
(Nitrogen present, 4.OE ;7 mg.)
Error c ic
4 085 4 082 4 088 4 082 4 090 4 080 4 080 4 082 4 088 4 090 4.085
Deviation from Mean Mg. 70 *0.000 -0,003 + O , 003 -0.003
-0.005 f0.001 +0.003
-0.12 $0.02 4-0.07
+0.005 -0.005 -0.005
-0,003 f0.003
+0.005
+o.oo
-0.07 $0.07 -0.07 f0.12 -0.12 -0.12 -0.07 $0.07 $0.12
complete rinsing of the condenser tube. The end of the condenser tube is then rinsed off with two 3-cc. portions of water and the flask is removed. The excess of acid is determined by titrating with standard alkali, using methyl red as the indicator. The flame is removed before the titration is made. As the generating flask, F , cools, the residue in A is withdrawn through Z. Successive rinsings with distilled water, introduced a t B , will be removed through Z as F continues to cool. Before using, the apparatus is steamed out thoroughly by distilling 100 cc. of water through it. As long as the flame is kept a t F no sucking back is caused by contact of steam on tube A and walls of G. The complete outfit may be mounted on one ring stand and thus is completely 15 CM.? portable. The total height , of 95 cm. (38 inches), including the burner, is no great inconvenience and is AM. compensated for by the simplicity of design and stability. The water used was distilled off alkaline permanganate until it showed no 'HOPKINS ammonia by Nessler's reBULB D agent. -The standard acid was prepared from constantboiling hydrochloric acid. The standard alkali was prepared from 50 per cent sodium hydroxide and standardized against Bureau of Standards acid potassium phthalate.
T h e apparatus described here is a modified form of the Kirk apparatus, simpler in construction and made more flexible by the use of standard taper joints. T h e construction of the apparatus is apparent from Figure 1. T h e volume of the distilling chamber is large enough to permit vigorous distillation without frothing and mechanical movement of solution into bulb
e
A. Operation The procedure follows the method given by Harte ( 3 ) . A sample, sufficient to yield 2 to 5 mg. of nitrogen, is digested in a 100-cc. Kjeldahl flask with sulfuric acid and any of the well-known catalysts. When digestion is complete, the sample is cooled, diluted with 20 cc. of ammonia-free distilled water, and transferred to the distilling chamber, A , by means of the funnel, B. Both the Kjeldahl flask and the funnel are rinsed successively with three 5-cc. portions of water. Stopcock C is closed and the condenser tube, D,is immersed in a known quantity of standard acid in a flask, E (not shown). Sodium hydroxide (50 per cent) is added to the sample in A through B and the funnel is again rinsed down with three 5-cc. portions of water. This is adequate t o ensure complete removal of sample and caustic from the funnel and bulb, A , to the distilling chamber, A . Although the apparatus has been found entirely satisfactory as described, a tip attached to funnel B , extending into bulb A , as discussed by Redemann ( 7 ) , represents a possible modification. The distilling tube, A , is now about onethird full. A 200-cc. round-bottomed flask, F (not shown), containing 100 cc. of ammonia-free distilled water, is connected to G. A flame is applied to F and the steam generated heats the jacket, H , preventing condensation in A , and enters the distilling chamber through tube I. This requires about 4 minutes' heating time. After allowing the distillation to proceed for 10 minutes, E is lox-ered and the distillation is continued for another 2 minutes to ensure
6
Performance T o test the performance, a standard solution of ammonium sulfate was used. Table I shows the results obtained by use of this apparatus. Shorter periods of time than those recommended give results which are in good agreement with the theoretical figures.
Literature Cited
I I P%o$ Lc.1
FIGURE 1. APPARATUS
133
(1) Allen, IND.ESG.CHEM.,Anal. Ed., 3,239 (1931). (2) Fife, Ibid., 8, 316 (1936). (3) Harte, Ibid., 7, 432 (1935). (4) Kemmerer and Hallett, IND. ENG.CHEM., 19, 1925 (1927). ( 5 ) Kirk, P. L.,Ibid., Anal. Ed., 8 , 2 2 3 (1936). (6) Pregl, "Quantitative Micro Methods", Philadelphia, P. Blakiston's Son & Co., 1937. (7) Redemann, IKD. EXG.CHEW,Anal. Ed., 11, 636 (1939).
