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LYT I CA L CHE M I S T R Y
they are snugly held by springs, and which serve as supports and as light shields to eliminate stray light. The emulsions are viewed through the glass panel in the front oi the rack. This panel is actually a glass photographic plate on which lines forming 100 vertical spaces in 7.5 inches have been printed. .In essential feature of the design is the discontinuous horizontal rulings. The light source consists of an incandescent filament mounted behind a 9 / g inch slit in a movable housing, so that it niay be positioned behind the emulsion to be examined. The slot in the front panel of the light housing is necessary to reduce stray light. The apparatus (Table I ) is assembled largely with tinner's screws. The printed glass plate is adjusted by means of screw slots in the lower glass guide, so that the zero line on the glass plates coincides with the upper side of the tube bottom. The prepared test emulsions are added to the tubes to a depth which corresponds to 100 divisions on the front glass pane! (16.75 cm., 7 . 5 inrhes), the 50-ml. graduate line on the Kessler tube not being used. After suitable aging, creaming, sedimentation, or oil separation of the test emulsions may be read as volume per cent directly from the glass screen in front of the tubes. This method provides a standard depth. The tubes are filled to an exact depth by pouring sufficieiit emulsion in the tube to give a slight excess, placing tube in viewer, and sucking out the excess emulsion with a glass tube attached to a vacuum system, adjusting the level accurately by the height at which the suction tube is held. A holder for the suction tuhe that rests on the front and rear top rails is a useful accessory. L
The ease of formation or of dispersion of an emulsion may also be estimated with the accessory tube support by holding a pipet a given distance above the surface of water in the Yessler tubes. The differences in extent of dispersion observed \Then various emulsifiable products are added in this uniform manner afford an estimate of the facility with which an emulsion may be prepared. The writers wish to acknowledge the assistance of Hon-ard Ferrier, who aided in the design of the component parts, and assembled the apparatus, and of George Huston, who prepared the drawings of the apparatus.
Q Figure 1.
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U I J
4pparatus
outside with nickel. The qtand for the receiving flmk ran I J ~ raised or lowered with one grasp. h tubing support prevents breakage of the condenser due to the weight of the heavy, waterfilled rubber tubing. Inlet tube H makes it possible to draw up mercury if the digestion procedure of Hiller, Placin, and Van Slyke [J.Biol. Chem., 176, 1401 (1948)] is used.
Warburg Vessel Rack. Roy E. Young, Division of Subtiopical Horticulture, University of Califoinia, Los .Ingeles 24, Calif. Micro and Semimicro-Kjeldahl Distillation Apparatus. Xolfgang Kirsten, Institute of 3Iedical Chemistry, University of Gppsala, Gppsala, Sweden.
,$KJELDAHL distillation
apparatus which favorably compares with other apparatus in speed and accuracy has been constructed in this laboratory. It is commercially available ( S o r stedt 8: Soner, Stockholm) and is in use in several Swedish laboratories. The layout of the apparatus is shown in Figure 1. -4 is an elect,rically heated boiling bottle with a three-stage switch, one for heating, one for distilling, and one for keeping hot (during lunch, etc.). G is a three-way st,opcock ryith one opening to L and one through J into a bottle or a sink. S is a spring rvhich holds joint N in position. Procedure. After the apparatus has been steamed out, G is turned so that the steam leaves through J . Stopper E is taken out and D is opened. The receiving flask, I , is placed under condenser C. The sample is introduced through E , followed by the sodium hydroxide. E is closed and the funiiel is filled with water. G is then turned so that the vapor passes through the distilling flask and D is closed. The distillation is finished after 5 minutes. Z is lowered, G is turned so that the vapor passes out through J ,and stopper E is taken out. Within 3 seconds all liquid from K has been drawn into L and the water from E has washed K and has also been drawn into L. D is opened, the next receiving flask is placed under C, and thc next sample is introduced and distilled in the same manner. The water in A boils continuously and no time is therefore lost in bringing it to boil or allowing i t to cool for draining of the apparatus. The time during which the distillation is going on can be used for the titration or for operating a second apparatus. Experienced analysts can operate three units a t the same time. Joint N and stopcock G should be lubricated carefully with silicone grease. The apparatus is made from borosilicate glass; the boiling hottle is of copper which is plated on the inside with tin, on the
troublesome featui es encountered with Kai bui g equipment have been eliminated in this laboratory hy the ube of the vessel rack desciibed. breakage of vessels, tipping over of the vessels when they are being filled, and maintaining the ~ . e s ~and I s plugs in order.
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CVERAL
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The vessel rack is shown in the diagram. I t is best made of stainless steel, which is easily cleaned and not damaged by accidental spillage of acid used in cleaning the vessels, but it may be made of aluminum with spring brass vessel clips. Ten vessels can be clipped to each rack, the renting plugs being placed in holes on one side and stopper plugs on the other side. Exact measurements are not given because the dimensions chosen n ill depend on the type of equipment used and the size of drying oven available. The size shown n-as made because six racks would fit in the drying oven available, and two racks of ten ves,.cls would fill the circular bath used. Plastic covers may be made t o cover the racks when they are not in use.
