ANALYTICAL EDITION
March, 1944
Table
Comparison of Composition of Single Flint Ball and Flint Rock Flour Produced during Jar Mill Grinding Single Flint Element Flour Pebble
IX.
...
11.7
0.06 1.5
0.06 6.6
...
4.7 5.0
0.2 0.0
0.0
Y/Q.
Y/Q.
Fe Zn cu
34 n co RI0
...
458. 6170. 25.7 6.3 0.35 10.0
20.9 49.3 98.8 1.71 0.4
205
Large increases in contamination of zinc, iron, copper, cobalt, and sodium resulted from decreai;e in size of plant samples ground in a jar mill using flint pebbles. For the types of mills studied, less contamination resulted from the grinding of vetch seed than from the grinding of oat grain. ill1 the mechanical grinding methods used resulted in serious contaminations of one or more elements. Although a particular mill may be used in the preparation of plant samples for the analyses of certain elements, it is concluded that marked errors would be involved in using the common mills for grinding plant tissue for general or extensive micro element analyses. ACKNOWLEDGMENTS
cobalt, and sodium. The use of porcelain or Mullite balls during jar mill grinding gave rise to appreciable contamination of iron, zinc, copper, cobalt, sodium, and in some cases calcium, sulfur, and phosphorus. Flint, porcelain, and Mullite balls all wear appreciably during jar mill grinding. The contaminating elements in flint rock flour are present in about the same proportions as in the contamination of R plant sample ground in the jar mill, using flint balls. Hand grinding with a mortar and pestle resulted in no appreciable contamination of iron, zinc, copper, boron, cobalt, manganese, molybdenum, calcium, sodium, magnesium, phosphorus, sulfur, or potassium. Grinding contamination is erratic for both jar and iron mills. A several-fold variation in iron contamination resulted from uniform Wiley mill grinding technique. TT’hile iron contamination of samples ground in a jar mill using Mullite balls is almost a straight-line function of loss of weight of the balls during grinding, the loss in weight is not uniform with time.
Glass Electrode
The Christy and Norris hammer mill and the porcelain burr mill were used through the courtesy of the Cornell University Departments of Agronomy and Biochemistry. LITERATURE CITED
Committee on Mineral Assay Methods, State Agricultural Experiment Stations and E. S. Department of Agriculture, “Recommended Mineral Assay Methods” (mimeographed report), Washington, D. C., Office of Experiment Stations, U. s. Department of Agriculture. Dana, E. S . , “Descriptive Mineralogy”, New Pork, John Wiley 8: Sons. 1928. Hamilton. T. S.,and Morris, H. P., 41st Rept. Illinois iigr. Expt. Sta., 133-6 (1928). Kirk, J. S., and Sumner, J. B., ISD.ENG.CHEX, 24, 454 (1932). ?;aftel, J. A , , ISD.ESG. CHEM.,. ~ N . L L ED., . 11, 407-9 (1939). Xakamura, F. I., and Mitchell, H. H., J . ,Vzitrition, 25, 39-48 (1943). Parks, R . Q . , Hood, S. L., Hurwits, Charles, and Ellis, G. H., ISD.ENG.CHEM.,AN.AL.ED.,15, 527-33 (1943). Purr, A., Biochem. J . , 28, 1907 (1934).
Assembly for Titrating Microbiological Vitamin Assays E. B. McQUARRlE
AND
H. J. KONEN Schenley Research Institute, Inc., Lawrenceburg, Ind.
IN
T H E titration of microbiological vitamin assays it is often more desirable to use a glass electrode pH meter to determine the end point than to use an indicator and note the color change. A simple assembly, using a well-known commercial glass electrode pH meter (Beckman, Laboratory Model G) and standard laboratory equipment, has proved very satisfactory in this laboratory, furnishing a simple and rapid accurate titration procedure.
A 7.5-cm. (3-inch) glass funnel with the stem cut off 1.25 cm. (0.5 inch) from its body and fitted with rubber tubing long enough to reach to a drain is supported about 7.5 cm. (3 inches) from the laboratory bench. A small piece of glass tubing connected to the compressed air line through a trap is placed in the funnel, so that the bottom tip of the tube is just in the stem of the funnel. The tip of a 25-ml. buret is inserted halfway down the funnel and over to one side. An external glass electrode and calomel electrode are suspended in the funnel about 2.5 cm. (1 inch) from the bottom and slightly off center. il pinchclamp is inserted in the rubber tubing line just below the stem of the funnel. To titrate an assay, the pinchclamp is put in place and the air turned on, so that a steady stream of bubbles will emerge from the air tube. The assay medium is poured into the funnel and the assay tube is washed with 10 to 12 ml. of distilled water, which is also added to the funnel content. The electrometric titration is carried out in the customary manner. The funnel is then drained by opening the pinchclamp, and the assembly is ready for the next titration. ACKNOWLEDGMENT
The authors wish to thank Eli Stevens for technical assistance in the preparation of the illustration.
k
Rubber Tu&ng
