INDUSTRIAL A N D ENGINEERING CHEMISTRY
April 15, 1931
been kept in stoppered reagent bottles under ordinary laboratory conditions have shown no evidence of decomposition or loss of reactivity over a period of several months. I n addition to their keeping qualities under ordinary laboratory conditions, egg albumin-iodoeosin and egg albuminbasic fuchsin fulfill the necessary conditions with respect to minimum degree of re-adsorption and acid or alkali fastness. These advantages, together with their relative ease of preparation, demonstrate their possibilities in qualitative tests
151
for proteolytic activity and lead to the belief that such substrates will be found more satisfactory than carmine-fibrin and Congo red-fibrin. Literature Cited (1) Hawk, P. B., and Bergeim, Olaf, “Practical Physiological Chemistry,” p. 210, Blakiston, 1926. (2) Hawk, P. B., and Bergeim, Olaf, Ibid., p. 259, (3) Hawk, p. B., and Bergeim, Olaf,I b i d , , p. 56. (4) Koch, F. c., and McMeekin, T. L., J . A m . Chem. s ~ c 46,2068 ., (1924).
Absolute Determination of Nitrogen in Organic Compounds’ Pregl’s Micro-Method Otto R. Trautz and Joseph B. Niederl DEPARTMENT OF CHEMISTRY, NPW YORK UNIVERSITY,
F ALL the methods in
NEW
YORK, N. Y .
The accuracy of Pregl’s micro-Dumas method may to keep the degree of purity of organic microanalysis be increased by using measured amounts of carbon the carbon dioxide constant. the absolute nitrogen dioxide and Copper oxide, and aPPlYing empirical corThe Kipp of Figure 1 can be rections for air and absorption errors. Wall adhesion determination enjoys perhaps evacuated and can then dethe greatest use and the field (0.5 Per cent of the nitrogen volume collected) and liver carbon dioxide containof its application in organic vapor pressure of the Potassium hydroxide solution ing onlv 0.001 cc. imDuritv in are considered. and bioidgical as well as ih in1 6 cc”. c a r b o n dioxfde. dustrial research is steadily Other satisfactory arrangeincreasing. Quite a number of investigations have been deal- ments are described by, Niederl, Trautz, and Saschek (4), ing with the various phases of the method in order to explain and by Lindner (S), Diepolder (I), and Hein ( 2 ) . The comand eliminate sources of error. The following comprehen- bustion tube and the azotometer are filled according to disive description of the analytical apparatus and procedure rections given by Pregl(5). may be of assistance, therefore, to those availing themselves Method of this reliable and quick method for the determination of nitrogen. A sample of 3 to 5 mg. is weighed on a standard microApparatus chemical balance (sensitivity 0.001 mg.), or on an ordinary The analysis train, as shown in Figure 1, consists of a analytical balance (sensitivity 0.1 mg.) making use of the Kipp carbon dioxide generator, gasometer, combustion tube, dilution method (4). For the introduction of the sample into CT,two-way stopcock, E, and precision azotometer. The the combustion tube Pregl’s (6) instructions are followed, care acid of the Kipp must be guarded from contact with air in order being taken that for each analysis the same amounts of the coarse and especially of the fine copper oxide are used. 1 Received November 20, Then the air in the combustion tube must be eliminated by 1930. Presented under the title passing one gasometer charge of carbon dioxide through the “Improvements in the Microsystem while cold (stopcock E open to the atmosphere), Dumas Method” before the Division of Physical and Inorganic If near the end of this operation, which should require about Chemistry at the 79th Meeting 5 minutes, stopcock E is opened to the azotometer, small of the American Chemical Somicro-bubbles (not larger than 0.2 of one division) should ciety, Atlanta, Ga., April 8 to appear in the azotometer. 12, 1930.
0
Figure 1-Diagram
of Apparatus
Vol. 3, KO. 2
ANALYTICAL EDITION
152
In the next operation, the actual combustion, stopcock D of the gasometer is closed, stopcock E opened to the azotometer, the long burner TB is lighted, and the combustion tube heated to red heat. Then the Bunsen burner, BB, is lighted, the heating of the temporary charge is started a t the empty portion of the tube, and the flame gradually moved nearer and nearer to the long burner. The rate at which the bubbles enter the azotometer must not exceed 2 bubbles in 3 seconds, and this rate is carefully regulated by the proper movement of the burner. During the combustion the gasometer is refilled with carbon dioxide to a mark between 50 and 100 cc. (50 cc. have been found to be sufficient) When no more bubbles rise in the azotometer, the combustion is at an end and the gaseous combustion products must be conveyed into the azotometer by a current of carbon dioxide; stopcock D is carefully opened and adjusted to give a rate of one bubble per second for the 10 minutes. During this the temporary charge is again heated throughout with the Bunsen burner to insure complete combustion. The burner is moved in the same direction as before and then extinguished. The remainder of the gasometer charge can be passed through the system at a higher rate, about 3 bubbles per second, and as soon as the current of gas has ceased, because of the absence of pressure in the system, stopcock E is closed and the long burner extinguished. After 15 minutes, the readings are taken of the nitrogen volume in the azotometer, to within 0.001 cc., with the potassium hydroxide leveling bulb at the height of the meniscus, and of its temperature to within 0.5" C., with the bulb of the thermometer touching the wall of the measuring capillary, and of the barometric pressure to within 1 mm. In order to determine the air and absorption errors-i. e., that volume of gas collecting in the azotometer during an analysis, which originates from the air content of the carbon dioxide used and from air absorbed to the temporary chargea blank analysis is carried out combusting a nitrogen-free substance (a few milligrams of pure cane sugar) in exactly the same way as in the actual analysis. The sum of the air I
and absorption errors is deducted from the azotometer readings obtained in the actual analyses and should be determined as often as any changes in the Kipp apparatus or in the procedure of the analysis are made. Calculation
To the volume reading, the calibration correction of the azotometer (from the apparatus certificate) is first applied. From the resulting volume deduct: (a) the correction for air and absorption,errors (from the blank analysis) ; (b) 1.1 per cent-i. e., 0.5 per cent for adhesion of the potassium hydroxide to the wall, thus reducing the volume of the gas in the capillary of the azotometer (6); 0.3 per cent for the vapor pressure of the potassium hydroxide solution (50 per cent) ; 0.3 per cent (approx.) for the temperature reduction of the barometer reading (from 18" to 0" C.). The resulting nitrogen volume is reduced to normal conditions (760 mm. and 0" C.) and the percentage of nitrogen calculated. o-Toluamide sample, mg... . . . . . . . . . . . . . . . . . . . . . . . . . . Collected nitrogen, cc., (at 24.5" C. and 767 mm.) ............................ 0.321 Calibration correction, cc.. . . . . . . . . . . . 0.001 Air and absorption correction, cc.. . . . . . 0.008 1.1 per cent correction, cc.. . . . . . . . . . . . 0.003 Total corrections.. .......................... .O. 012 Net volume nitrogen to be reduced to normal conditions, cc... . . . . . . . . . . . . . . . . . . . . . . . . . . 0.309 Nitrogen found, yo.. . . . . . . . . . . . . . . . 10.33 Nitrogen calcd., yo.. . . . . . . . . . . . . . . . 10.37
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3,475
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Literature Cited (1) Diepolder, Chem.-Zlg., 43, 353 (1919). (2) Hein, 2. angew. Chem., 40, 864 (1927). (3) Lindner, Be?., 59, 2806 (1926). (4) Niederl, Trautz, and Saschek, Mikrochemie, Emich Festschrift, 227 (1930). (5) Pregl, "Quantitative Organic Microanalysis," Blakiston, 1924; Springer, 1930. (6) Trautz, iMikrochemze (1931).
Measurement of Consistency of Starch Solutions' J. C. Ripperton HAWAIIAGRICULTURAL EXPERIMENT STATION, HONOLULU, HAWAII
A study of the swelling of starches and its relation viscosity methods ordinarily HE consistency of t o viscosity has been made and a method of evaluating used, was devel.oped for starch s o l u t i o n s is starches by the swell method using a very simple factory control purposes. quite generally deterapparatus devised. mined by some type of visThis method is applicable chiefly to the tuber starches Preparation of Solution cometer or plastom'eter. with a large swell, such as those of potato, sago, arrowThese vary in principle and root, and to a lesser extent to cassava starch. It is well known that starch design, but they have 8s their exists as granules, rather than purpose the measurement of the internal resistance to flow of the viscous or plastic solution. as a homogeneous powder. When heated with water these Emulsoid colloids, such as starch, owe a large part of their vis- granules imbibe water and swell greatly. I n the natural cous properties to swelling on imbibition of water. Determina- starches, each granule exists as an inflated balloon consisting tion of this ability to swell was used by Harrison (1) as a meas- of a skin, called amylopectin, and a milky colloidal liquid ure of the consistency of the starch solution. Measurement of within, called amylose. If the solution is sufficiently dilute, the swelling of starch as an index of its strength has been used the swollen starch grains will settle on standing, leaving a occasionally but has never received general recognition. I n clear supernatant liquid. With increasing concentration, the course of an investigation to determine the relative proper- the granules fill more and more of the space until no settling ties of edible canna and potato starches, a study was made can occur. The starch solution begins to take on noticeof the swelling method and its relation to viscosity. The able viscosity when the swollen granules fill all the liquid method described, which has certain advantages over the space. It is common knowledge that when a starch solution is stirred or agttated vigorously it becomes less viscous and can 1 Receivrd November 7 , 1930
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