1138 The principle of the Ilartridge-Roughton mixing apparatus
( 4 ) has been employed. Two 1-ml. tuberculin syringes with equal bore are fixed in a parallel position with Lucite plates by means of rubber gaskets, Surrounding the syringes and fused to the Lucite plates is a cylinder of Lucite 7 em. long and 4 em. in diameter with two outlets. This forms the water jacket, wj, which is connected in series with the cooling coils, cc, and the water bath, wb. The syringe plungers are coupled to a block of Lucite, p , with adjustable plastic screws to allow proper positioning of the plungers. Two plunger guides, p g , on either side of the water jacket, consisting of brass rods in Lucite tubes, permit the plungers to move smoothly. Fixed to the upper edge of the Lucite plates with sealing was are two Feparatory funnels acting as reservoirs for the enzyme, re, and substrate, rs. The entire apparatus is fused to a Lucite plate clamped to the phototube housing unit with brass screws and is readily removable. Each separator?. funnel is connected to the corresponding tuberculin syringe by means of a S o . 18 needle, 1-mm. plastic tubing, and a glass T-tube. From the lower limb of the T-tube extends a short piere of plastic tubing through a pinch clamp, p c , into the cuvet,te inside the housing unit. The front of t,he cuvette housing unit has been cut away and replaced with a removable brass plate, r p . This permits removal of the cuvettes without disturbing the arrangement of the mixing apparatus.
ANALYTICAL CHEMISTRY cuvette before the s)-ringes are emptied, complete mixing of t h e two solutions is assured. However, in the event solutions are being added to material already in the cuvette, it may be necessary to agitate the mixture either with a stirrer or by forcing a few bubbles or air with a syringe, as, by means of a long needle through the solution. Temperature nieasurements are readily made with a copper-constantan thermocouple fused in a capillary tube which, because of its small heat capacity, does not introduce any serious error. Both the air needle and the thermocouple can be easily inserted into the cuvette through small holes adjacent to the pinch clamp. Such an apparatus permits quantitative continuous readings of optical density beginning a fern seconds after mixing of t h e ieaction components. ACKNOWLEDGMENT
The authors wish to acknowledge the technical assistance of IVilliam Strovink in the construction of this apparatus. LITERATURE CITED
(1) Beers, R. F., Jr., and Siser, I. W., Fedemtion Proc., 11, 11 (1952). (2) Beers, R. F., Jr., and Siser, I. IT., J . Biol. Chem., 195, 133 (1952). (3) Beers, R. F., Jr., and Sirer, I. W'., J.Phys. Chem., 57, 290 (1953). (4) Hartridge, H., and Roughton, F. J. TT., Proc. Roy. SOC.London, A 104,376 (1923). WORKdone under a postdoctoral fellowship of the American Cancer Society recommended by the Coninlittee on Growth of the National Research Comcil.
Improving the Illumination of Opaque Objects for Microscopical Study. Willard L. Scott, 115 Arlington Ave., Jackson, Tenn. method consists of the construction and application of a Tdiffuser for improving the illumination of opaque objects, It is recommended for microHIS
using powers up to 1OOX. scopes not equipped \\ ith vertical illuminators but relying solely on inclined illumination, outside the objective, such as the stereoscopic wide-field binocular types. With this type of equipment, the method has proved it. value in studying grain structure of metals. I n the metallography of aluminum and aluminum alloys, the grain structure is easily seen, after annealing and etching, a t the lower powers from 60x to 1OOX. X concentrated beam, or spotlight, will illuminate the ohject and reveal the grain boundaries; however, the structure inside the grain is lost, owing to glare and high lights from the surface. This difficulty can be obviated in the following way. Cut a strip of paper 3 inches long and 0.75 inch wide. Scotch tape the ends together, forming a paper ring. Place the paper ring over the surface of the object. Direct the beam, or spotlight, on the paper ring diffuser. Focus the microscope on the illuminated area inside the paper ring diffuser.
The syringes are filled after the pinch clamp is closed and the stopcocks are opened, and are emptied into the cuvette after the above procedure is reversed. Quantities as small as 0.05 ml. can be measured accurately by this device. The coupling of the syringes assures that equal amounts of each reagent are added to the cuvette. The removal of air bubbles from the apparatus is facilitated by tipping. Water is pumped through the water jacket and the cooling coils of the Beckman spectrophotometer a t a rate of approximately 1 liter per minute. Temperature equilibrium in the syringes from 0" up to 50' C. is reached within a minute. There is no measurable heat transfer through the needles and T-tubes. Because of its large heat capacity, a three-way stopcock vias not used. If there is no liquid in the
The diffuser will emit multidirectional rays, illuminate the surface evenly, and eliminate the glare and high lights. Each minute surface will have greater potentialities for reflecting its rays into the microscope, thus revealing the detailed structure inside the grain. The paper rings may be altered as to size, shape, color, and translucency. The spotlight may be focused on the paper ring diffuser a t different points, from different angles, and with different degrees of intensity. This will be determined by actual test and !\-ill vary with different types of materials. The diffuser may be constructed from translucent materials other than paper. This method is recommended for other opaque objects similar to those encountered in the study of metals and alloys. The time factor and cost are negligible.
