364
ANALYTICAL CHEMISTRY
are shown in Table I. The fact that the hydrogen content in series D is very low indicates that tin-coating does not increase the hydrogen content. The fairly consistent results obtained in series C and D indicate the reproducibility of the analysis of the tin-coated specimens. However, in both series the first result is somewhat higher than the others. This is probably due to the effect of tin vapor. A simple and fairly reliable method has been proposed for the storage of solid steel samples until they can be analyzed foi hydrogen by the vacuum fusion method LITERATURE CITED
,(1) Carter, S. F., Elec. Furnace Steel, 7,267 (1947). (2) Derge, G., Peifer, W., and Richards, J. H., Trans. Am. Inst. Mining Met. Engrs., 176,219 (1948). ,(3) Walter, D. I.,ANAL.CHEM.,22, 207 (1950). (4) Wells, J. E., and Barraclough, K. C . ; J. Iron and Steel Inst., 155,27 (1947). PCBLISHED by permission of the director-general of Bcientific Services, Department of Mines and Technical Surveys, Cansds.
Simple Laboratory Evaporator. Paul Sumerof and Karl Reinhardt, Spuibb Institute for LIedical Research, New Brunsuick, IT.J. wo devices for the concentration of solutions have appeared
T recently in the literature [Craig, L. C., Gregory, J. D., and Hauamann, W., ANAL.CHEM.,22, 1462 (1950); Partridge S. hl., J . Sci. Instruments, 28,28 (1951)l. This apparatus is a modification of the evaporator described by Partridge; the major difference is in the type of bearing used to rotate the flask. By using -thP plunger and housing of a standard syringe for the bearing, it has been found possible to eliminate the special packing glands required in the Partridge apparatus. With the exception of the rubber stoppers, the apparatus, as shown in the diagram, is of all-glass construction. Additional flexibility is provided in that .almost any standard electrically driven stirrer may be used as a sourre of power, so that the motor is available for other uses when the evaporator is not in operation Apparatus. Housing, A , consists of 40-mm. (outside diameter) borosilicate glass tubing 62 mm. long with a side arm attached a t the midpoint. The dimensions are not critical. Part B consist8 of the outer portion of a standard Becton-Dickinson 20-ml. Pyringe with three slots 8 mm. wide X 22 mm. long cut into it. These slots were cut with a circular wet-bonded abrasive glass cutting wheel. The slots are staggered so that each one occupies one third the c i r c u m f e r e n c e. Part D is the inner portion of the syringe with the top removed and with slots cut, to match thosein B. A 7-mm, glass rod, H , flattened at one end, is put, through a KO.0 rubber stopper; the flat end is placed so that it rests against the smaller surface of the stopper. Joint E is a 24/40 male joint constricted to an opening of 10 mni. The end of this tube is extended 10 mm. beyond the No. 3 stopper, F. This extension serves as a trap and keeps any glycerol, which is used as the lubricant, from running back into the distillation flask. Part I is a small piece of wire twisted around F, and serves as a hook for connecting springs or rubber bands to a flask (not shown on the diagram). With the S o . 0 stopper a t the top of D, it is possible to slide the entire inner unit in and out of B without disassembly. Cleaning of the apparatus is thus facilitated. Operation. To operate, housing A is clamped a t about a 45” angle, the solution to be concentrated ie placed in the flask, barrel D is lubricated with glycerol, and t’he entire unit is inserted in B. The shaft of an electrically driven laboratory stirrer is connected with a short piece of rubber tubing t o H . A water bath is placed
under the flask to relieve any strain on the apparatus and to serve as a source of heat for evaporation a t elevated temperature. The vacuum obtainable with this apparatus depends on the fit of parts B and D of the syringe. Among several units which have been made, the vacuum obtainable with a mechanical vacuum pump has varied from 5 to 25 mm. of mercury. A few drops of glycerol added occasionally to the upper part of D where it protrudes from B serves to maintain the vacuum. Although the rate of rotation of D may be varied by using a variable speed stirrer, a speed of 60 r.p.m. has been found to be convenient. The apparatus has been useful in evaporating the many fractions resulting from chromatographic separations. For samples coatained in small vessels joint E may be provided with reducing adapters. Although no provision for recovering solvent is shown on the diagram, a condenser and receiver may be installed between the housing, A , and the vacuum pump.
Determination of Urea Nitrogen in Whole Blood by Heating in a Pressure Cooker. Andre C. Kibrickl, hl. R . Ross, and S. J. Skupp’, Department of Chemistry, The Bronx Hospital, New York, K. Y. and Mandel ( 3 ) have recently adapted the writers’ method ( 2 ) to the determination of urea nitrogen in whole blood. I t has been found that it is necessary to use gluconate to stabilize the nesslerized solutions if the Nessler’s reagent is prepared according to Bock and Benedict (1). This contradicts thcl esp~rienceof Thompson and Morrison (4)that a Nessler’s solution prepared directly from mercuric iodide and potassium iodide is more likely to give cloudy solutions. Mercuric iodide, llcrck reagent, is satisfactory in the preparation of the reagent. However, the mercuric iodide and potassium iodide must be dis3olred in about one fifth the volume of water and then dilutedm-ith thr remaining amount of wat’er and sodium hydroxide solution. Otherwise, the salts may be very difficult to dissolve. The solution.~which have been obtained with the reagent described by Hawk, Ospr, and Summerson ( 1 ) w r e always crystal clear for at least 45 minutes when the determination was performed as follows: WINBS
One milliliter of Folin-FVu filtrate was heated with 0.5 ml. of
1 JT phosphoric acid in a pressure cooker at 20 pounds per square
inch pressure for 75 minutes. One milliliter of 0.9 N sodium hydroxide was used for neutralization, and 1 ml. of the Nessler’s reagent was added to the solution after dilution to 10 ml. Actually I hour’s heating is adequate in a Xational Presto cookercanner, No. 5, since some time is required for the tubes to reach a pressure of 20 pounds per square inch and then to return to atmospheric pressure. I n heating time there is little discrepancy between these findings and those of Owings and hlandel(3). The colorimetric readings may be made in an Evelyn colorimeter with filter 515, a Klett-Summerson colorimeter with filter 50, or it Lumitron colorimeter with filter 530. In each case standard curves were found to follow Beer’s law. The slopes of the rurves in optical density per milligram per cent of urea nitrogen were 0.0072 for the Evelyn, 0.0056 for the Klett-Summerson, and 0.0047 for t,he Lumitron colorimeters. Filter 50 was required for the Klett-Summerson colorimeter since filter 51, which is generally used for nesslerized solutions with this inatrument, n-:M found t o yield a slope of 0.0035 with the more dilute solutions. LITERATURE CITED
P. B., Oser, B. L., and Summerson, W. H., “Practical Physiological Chemistry,” 12th ed., p. 1230, Blakiston, Phila-
(1) lIank,
delphia, 1947. (2)
Kibrick, A. C., and Skupp, S.,Proc. SOC.Exptl. Bid. Med., 73,
432 (1950). (3) Owings, R. H., and Mandel, E. E., I b i d . , 78, 363 (1961). (4) Thompson, J. F., and Morrison, G. R.. .INAL. CHEY.,23, 1153 (1951). 1 Present address, Department of Chemistry, Xew York University College of lledicine, K e a York, X. T.
