June, 1925
ISDCSTRIAL ALVDENGINEERING CHEMISTRY
On the other hand, Dr. Benedicks has secured chemically more inert conditions, a better opportunity for eliminating errors due to surface tension, and an opportunity of checking density a t the freezing point by independent means.
649
The writer experienced difficulties with the contact points when working on high phosphorus metal, which might have been avoided by the use of the Benedicks method of protecting this part of the apparatus.
An Improved Calomel Electrode' By C . J. Schollenberger OHIOSTATEUNIVERSITY, C ~ L U M BOHIO W~.
COMPACT and nearly troubleproof calomel electrode for electrometric work is easily constructed on the plan of the sketch. The body of the electrode vessel was made from a small separatory funnel by removing the stopcock and fusing on a piece of glass tubing about 3 cm. long. The inner tube is of such diameter as to fit rather closely in this. The joint between is made tight by wrapping a strip of paper about the tube before it is forced into place. -4little paraffin melted in the tube will make it tight enough to hold mercury and prevent the escape of the potassium chloride solution. A fused glass joint would be better, but is beyond the skill of an amateur glass-worker. The ground-in plug a t the bottom is most important, and the grinding should be carefully done with fine emery and water. The ends of both plug and shell are afterwards ground down SO that they will be flush, and with the accurately ground part a t 1 the tip of the tube. When the electrode vessel is completed, the stem of the plug is cut off a t such length that when the Detud of H rubber stopper is in place it will -E exert some pressure upon the plug. A well-ground plug will permit so littledeakage that no visible diffusion-of the saturated potassium chloride is evident when the tip is immersed in a test tube of water and held to Cenhmefer Sco/e the light. Contact with the mercury of the electrode is established through a slightly bent glass tube with platinum wire fused in the end and containing a little mercury, into which the wire leading to the potentiometer is inserted. To fill the electrode vessel the space between the inner tube and d in end and partly fit$ the stem of the plug is first partly mercury, for connection to filled with saturated potassium potentiometer B-ParaBned rubber stopper, chloride, which may be drawn No. 00 or 0 Crystalline C-Approximate level of potas- up from the tip. sium chloride solution potassium chloride lis carefully D-Calomel E-Mercury placed in the inner tube from F-Joint made tight with paper above by means of a little paper and para511 &Approximate level to which tube is filled with KCI crystals SCOOP. Care should be taken H ~ G r o u n d - i n plug for liquid that the plug is not lifted in doing junction I-Glass ,,rod, about 2.5 mm. this, as a crystal2 between the diameter, with bead fused on end, and ground in t o make plug H . ground Surfaces is &&Cult t-0re-
A
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Upper end is afterwards c u t off and rounded in flame
1 Received
February 5, 1925.
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move and will cause persistent leakage. When the inner tube is filled with the crystals and liquid, a little dry filter paper is forced into the slightly flared opening above, in order to keep the calomel out of this tube. The mercury and calomel are now added, with sufficient saturated potassium chloride to fill the cell. After the calomel has settled, the filter paper is removed with forceps and the paraffined rubber stopper bearing the bent tube to establish connection with the mercury is put in place. When not in use the tip of the ground joint should be kept in water, as crystallization of the salt here may cause the joint to leak and is certain to cause diffusion potential for several minutes when the electrode is again used. The design is not novel, as a similar one is figured in the apparatus catalogs; the use of a ground-glass plug for making the liquid junction is mentioned by Lamer and Parsons,2 who state that, although diffusion potential may not be prevented, the contact is perfectly reproducible and is satisfactory in use. It has the great advantage that very little of the salt can escape into the solution under test, especially important in soil work. No separate salt bridge is necessary, as the ground tip is simply placed in the liquid under test, beside the electrode. A calomel electrode constructed as described has been satisfactory in soil work, using the quinhydrone electrode, and is considered well adapted to all electrometric titrations in which a saturated potassium chloridecalomel electrode can be used. 2
J. B i d . Chem., 67, 613 (1923).
Calendar of Meetings American Leather Chemists Association-22nd Annual Meeting, Hotel Traymore, Atlantic City, N. J., June 3 to 5, 1925. Third National Colloid Symposium-University of Minnesota, Minneapolis, Minn., June 17 t o 19, 1925. American Society for Testing Materials-28th Annual Meeting, Atlantic City, N. J., June 22 to 26, 1925. American Institute of Chemical Engineers-Providence, R. I., June 22 to 27, 1925. Joint Meeting with British Institution of Chemical Engineers, Leeds, England, July 13 to 23, 1925. National Chemical Equipment Exposition-Providence, R. I., June 22 to 27, 1925. ,American Ceramic Society-Summer Meeting, Toronto, Canada, July 4 to 11, 1925. American Chemical Society-7Oths Meeting, Los Angeles, Calif., August 3 to 8, 1925. 71st Meeting, Tulsa, Okla., April 5 to 9, 1926. American Electrochemical Society-Fall Meeting, Chattanooga, Tenn., September 24 to 26, 1925. National Exposition of Chemical Industries-New York, N. Y., September 28 to October 3 , 1925. Institute of American Meat Packers--ilnnual Meeting, Chicago, Ill., October 16 to 21, 1925.
