J. T. Stock and A. V . DeThomas University
of
A "Direct Attachment"
Connecticut
Storrs
Kieldahl Apparatus
The speed and reliability of the modified form of the Kemmerer-Hallett form of Kjeldahl apparatus arise largely from operative ~implicity.'.~No quantitative transference of corrosive liquid is necessary; the digestion flask containing concentrated sulfuric acid, a catalyst, and ammonium salt formed by the destruction of the nitrogenous sample is attached directly to the distillation head by a standard-taper joint. The apparatus is all-glass and has the minimum of detachable joints. These features, highly desirable for advanced or routine work, cannot be achieved without expense. Both initial and replacement costs are therefore likely to weigh against acquisition of multiple sets needed in beginning courses in analytical chemistry. Because of the ready attack on cork or rubber by sulfuric acid, it seems that any simplified apparatus that uses the "direct attachment" principle should retain the standard-taper joint between flask and distillation head. During the distillation, this joint becomes hot and probably receives alkaline spray. While an experienced operator will remember to disconnect the joint as soon as distillation is complete, a beginner who lets the apparatus cool with the flask still attached may find the joint firmly "frozen." No complicated or large special glass parts are involved in the apparatus shown in the figure. After completion of digestion and cooling of flask A , a Teflon taper sleeveais slipped on the cone of distillation head B. The latter is then attached to the flask; two springs (not shown) stretched between sealed-on hooks prevent the joint from opening. The glass center tube, through which sodium hydroxide solution and then steam are introduced, may be slid up and down in rubber tubing sleeve C . This accommodates flasks that are not of identical length. Alkali is delivered from funnel D, which has a Teflon stopcock. When this is closed and clip E is tightened, steam entering as shown is forced to pass through the now-alkalme solution in A . Steam and ammonia pass over into the condenser; provided that distillation is not excessively rapid (the desirable rate is between 3 and 4 ml per min), spray is effectively arrested by the deflector in B. This is shown enlarged in ( a ) ; the inner end of the exit tube is closed, so that vapor must leave through two diametrically-opposed holes as shown. Trap F , made from a 200 X 38-mm boiling tube, prevents the contents of A from being
sucked into the steam generator if the heating of the latter is discontinued. Release of clip E allows the trap to be emptied and interrupts the flow of steam through A. To provide for ready use and easy dismantling for cleaning, the apparatus shown and the associated vertical condenser are mounted on a rectangle of '/rinch thick plywood. Dimensions are such that the bulb of flask A, top of funnel D, extremity of the steam inlet tube, and stem of the condenser below the water jacket project beyond the board. A facing of Formica or similar sheet is a desirable but not essential feature. Spring clips firmly retain A, D, F and the condenser; the latter is further secured by its tubulures, which pass through the board, so that water and waste connections may be made a t the hack Most of the joints are glass-to-glass beneath rubber tubing sleeves, as shown. Two 3-in. lengths of 6/,-in. diameter hardwood dowel rod project from the back near the top and bottom of the center line. These allow the board and its equipment to be mounted in clampholders a t the desired height on a heavy-based ring stand. This apparatus was developed with the partial support of the National Science Foundation's program for the design of science teaching equipment.
KEMMERER, G . , A N D HALLETT, L. T., Znd. Eng. Chem., 19, 1295 (1927).
Fisher Scientific Co., Catalog 59, 968 (1959). Arthur F. Smith Co., 311 Alexander St., Rochester 4, N. Y.
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