JULY 1.5, 1936
ANALYTICAL EDITION
determined separately and treated as a known quantity. The other acids are determined in the presence of formic acid.
Literature Cited (1) Auerbach, F., andZeglin, H.,Z. physilz. Chem., 103, 161-77 (1922). (2) Duclaux, E., Ann. d. 2’Ecole h’ormale Supbrieure, 2, 270 (1865); Ann. chim. phys., 2, 289 (1874); Trait6 d e Microbiologie, 3, 384 (1900). (3) Olmstead, W. H., Whitaker, W. M., and Duden, C. W., J.Biol. Chem., 85, 109 (1929).
275
(4) Osburn, 0.L., W-ood, H. G . , and Werkman, C. H., IND. ENQ. CHEM.,Anal. Ed., 5, 247 (1933). (5) Virtanen, A. I., and Pulkki, L , Ann. Acad. Sci. Fennicae, 29A, No. 25 (1927); J. Am. Chem. SOC.,50, 3138 (1928). (6) Weihe, H. D., and Jacobs, P. B., IXD. ENQ. CHEM.,Anal Ed., 8, 44 (1936). (7) Werkman, C. H., IND. ENQ.CHEM.,Anal. E d . , 2, 302 (1930); Iowa State Coll., S. Sci., 4, 459 (1930); 5, 1, 121 (1930). RECEIVED April 3, 1936. Paper J-191 of the Iowa Agricultural Experiment Station. Project 67.
An Overhead Heater for Rapid Evaporation, Drying, and Charring LESLIE F. NIMS
AND
M. K. HORWIT”, Yale University School of Medicine, New Haven, Conn.
The heater is made from the top unit (17.5 X 35 cm., 7 X 14 inches) of a muffle furnace (multiple-unit furnace, Type 56, Hevi Duty Electric Co.), with the radiating face of the unit protected by a sheet of stainless steel (Ka2SMO of the Crucible Steel Co. or equivalent is satisfactory). The apparatus is supported on two ring stands by a suitable brass framework. The heating unit is connected directly to a 220-volt line and draws about 17.5 amperes when hot. Under these conditions the radiating Burface becomes a bright cherry red. The amount of heat received by the dishes is regulated by raising or lowering the unit. The efficiency of the radiator could be increased by thermal insulation for the top surface, but it has been found convenient to use the top surface as a high-temperature hot plate. A smaller unit (top unit of a multiple-unit furnace, Type 52), 12.5 X 25 cm. (5 X 10 inches), drawing 10.5 amperes when connected directly to 110 volts, has proved useful for analyzing samples in small crucibles.
FIGURE 1. RADIANT HEATER A S USEDFOR EVAPORATION OF FLUIDS
In Table I are given the times necessary to complete t h e procedures there listed. The radiant heater would be especially useful in those methods that require frequent evaporations, such as microdeterminations of bromine or iodine in biological materials, where as much as 24 hours may be saved on a single analysis.
Hot plate aerves only as convenient support for dishes
T
HE foaming, spattering, and creeping of fluids that often accompany some of the procedures in quantitative analyses can be obviated by the proper application of heat ( I ) , Figure 1 illustrates a simply constructed overhead heater, made from a standard commercial unit, sufficiently large to allow the simultaneous treatment of ten 50-cc. or four 200-cc. samples. With this apparatus, troublesome evaporations can be carried out expeditiously-for example, 200 cc. of urine can be taken to dryness in half an hour with no signs of ebullition or foaming. Materials such as casein, blood, and sugar, which are difficult to ash by the usual methods, can be quickly dehydrated and charred under the heater. The residues may then be safely placed in a hot muffle furnace t o complete the ashing.
TABLEI. TIMEREQUIRED Material
Operation
Time
Mi%. Water Urine Blood
Evaporate 200 cc. to dryness Evaporate 200 cc. to dryness and char Evaporate 10 cc. t o dryness char, add 1 cc. of concd. nitric acid and evaiorate to dryness Casein 10 grams plus 70 cc: of water and 4 cc. of 8 N potassium carbonate. Evaporate to dryness and char Sodium chloride 0.5 gram plus 2 co. of concd. sulfuric acid. Evaporate to dryness and heat to cessation of fuming Glucose 10 grams, thoroughly charred
30 45
45 60) 90) 40,
Literature Cited (1) Fresenius, C. R., and Cohn, A. I., “Quantitative Chemical Analysis,” pp. 86,87, and 90, New York, John Wiley & Sons, 1903. RECEIVED May 9, 1936.
