Improved Steam-Distillation Apparatus c. V. BOWEN AND W. F. BARTHEL Bureau of Entomology and Plant Quarantine, United States Department of Agriculture, Beltsville, Md.
T
HE deterniination of nicotine b y the conventional
This still has i m n y advantages over the conventional apparatus. The compact construction alloivs for setting up batteries where large numbers of determinations are to be made. The heating of the distillation chamber by the steam in the outer jacket, together with the entrance of steam a t the bottom of the inner chamber, eliminates the possibility of bumping. The apparatus is easily cleaned by drawing the spent sample into the steam jacket, rinsing well, and allowing the jacket to drain. The narrow inner chamber increases the length of liquid-vapor contact, thereby hastening the distillation. The ground-glass joint a t the top of the distillation chamber affords a means for introducing the sample, alkali, etc., aids in cleaning, and makes the apparatus less rigid, thereby diminishing the danger of breakage. It is possible to take much smaller samples than are ordinarily used for analysis. The volume of the distillate is dependent on the size of the sample used: 25 mg. of nicotine distilled quantitatively in 100 ml. of distillate and 50 mg. in 150 ml. The accuracy of the results obtained n ith the apparatus is shown in Table I. A nicotine solution was steam-distilled and titrated with a standard acid and compared r d i a direct titration of anothei portion of the same size. The efficiency of the still depends on the time during which the liquid and steam are in contact. The inner chamber is heated by the steam held by the outer jacket, while a t the same time the liquid-steam contact is much longer than in the conventional steam-distillation outfit. These two conditions much more than compensate for the absence of flame heating as in the usual apparatus. The efficiency is such that the nicotine may be distilled completely from a 2-gram sample of tobacco in 0.5 hour. This apparatus has also been used satisfactorily for the determination of nornicotine and anabasine, both of which are much less volatile n i t h steam than nicotine. The dimensions given n-ere optimum for the distillation of tobacco samples. Modifications, such as using a larger condenser, increasing the length or the diameter of the inner chamber, or changing the type of trap, may be desirable for some applications.
steam-distillation method (1) has long been known to have several decided disadvantages. The apparatus is bulky. Because bumping and foaming occur, considerable attention is required during distillation. Since a large volume of distillate must he collected, the time for distillation is rather long.
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TABLE I. COXPARISON OF STEAM DISTILLATION WITH DIRECT TITRATION FIGERE 1
(Using 0.02 S hydrochloric acid against nicotine) 10 hll. of Solution 5 M1. of Solution Titration of Titration of Direct titration distillate Direct titration distillate MI. MI. MZ. M1. 7.58 7.57 3.77 3.78 7.57 7.56 3.78 3.80 7.57 7.57 3.78 3.80 7.58 7.58 3.76 A\,. 7 .575 7.57 3.773 3.793
Kirk (2) has modified the Pozzi-Escot (3) apparatus in the construction of micro-Kjeldahl distillation apparatus. An adaptation (Figure 1) of this type of still has proved exceedingly satisfactory for t'he steam distillation of steamvolatile alkaloids on the macro scale. This modification requires the use of a separat'e steam generator.
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The sample is placed in the inner chamber, A , paraffin and alkali are added, and the trap and condenser are connected at, the glass joint, B , which is lubricated to prevent freezing. The initial volume of the sample and alkali should be as small as practical, preferably less than 25 ml. for an inner chamber with a total volume of 150 ml. Steam is driven in through C and passes into the inner chamber through D. The drain, E, is closed by rubber tubing and a pinchcock, and the distillate is collected at F. Where paraffin is added to prevent frothing, some will be carried over into the distillate; but in the case of alkaloids precipitated as silicotungst,ates and filt'ered through tared Gooch t'ype crucibles this offers no objection.
Acknowledgment The w i t e r s w e indebted t'o 0. 4. Selson for the glass blo\ving involved in making t,he apparatus described. Literature Cited (1) Assoc. Official .\gv. Chem.. Official and Tentative Methods of of Analysis, 5th ed., p . 64, 1940. ( 2 ) Kirk, P. L., ISD. Esva. CHEM., AXAL.ED.,8, 223 (1936). (3) Poazi-Escot, >I. E., Bull. SOC. chim., [3] 31, 932 (1904).
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