INDUSTRIAL AND ENGINEERING CHEMISTRY
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With the exception of nickel cyanide all the common insoluble cyanides tested respond to the cyanide test when subjected to the authors' procedure. Only in the case of silver cyanide does the method fail when applied to the sodium carbonate prepared solution, for the reason that the salt is not transposed by the carbonate treatment. It is particularly noteworthy that only lead cyanide responds to the direct Prussian blue test. It is thus evident that the separation must be carried out even when the interfering acids are definitely known to be absent.
Vol. 7, No. 2
SUMMARY
A method for the detection of cyanide is proposed that depends upon the separation of the acid by air displacement in a simple apparatus, followed by the application of the Prussian blue test. The method is sensitive to 0.2 mg. of cyanide and is applicable in the presence of ferrocyanide, ferricyanide, thiocyanate, carbonate, sulfite, thiosulfate, or sulfide. RECEIVED January 17, 1935.
A Simple Photoelectric Thermoregulator WILLIAML. WALSHAND NICHOLAS A. MILAS,Massachusetts Institute of Technology, Cambridge, Mass.
I
tentiometer. I n so doing, it INE cuts off the light fallin on the on the catalytic oxidaphotoelectric cell whic!, by a D RNACE t i o n of o r g a n i c subsuitable amplification, operates stances at temperatures bea sensitive relay, thereby bypassin a part of the current tween 100" and 500" C., it t,hroug% additional resistance. was found necessary to deAs the temperature of t h e velop a simple and inexpenfurnace decreases, the opposite sive device for the automatic effect is produced-. g., t h e galvanometer needle moves t o c o n t r o l of temperature, in - 115 V., D.C. N +I15 V., D.C. the right, thereby exposin the order to obtain reproducible FIGURE1. DIRECTCURRENT 23o-vOLT THERMIONIC RELAY photoelectric cell to the Bight results with the minimum exsource which is most convenA . G. E. 110-volt 60-cycle relay type C. R. 2810-1265-G1. A thin penditure of time. sheet of mica should be inderposed between the iron core of the iently rovided by a 40-watt solenoid and the control arm of this relay. This seems to be 110-voi desk l a m p p I a c e d Various temperature-coneffective in preventing sticking of the contacts. about 20 cm. (8 inches) above E . 48-Type vacuum tube trolling devices (1-12) utilizC. 22-Type vacuum tube the slit. ing either photoelectric cells D . PJ 22-Photoelectric cell E. 0.002-Mfd. condenser foil t y e or thyratron tubes have apThe photoelectric cell with L. LlO-Watt, 115-volt t u b t e n &ament G. E. Mazda lamp used as a convenient reslatant peared in the literature durthe system of amplification R i and Ra. 500-Ohm resistors i n g t h e p a s t few y e a r s . and sensitive relay is shown Rn. 400-Ohm resistor. Although, it might be best to have R I and Rz variable, this specification 1s not absolutely necessary. However, all these employ diagrammatically in Figure 1. R4. Grid leak, 1 megohm R5. Grid leak, 50 megohms very elaborate or expensive The entire apparatus-is asa u x i l i a r y apparatus such sembled in a v e n t i l a t e d as mirror galvanometers and other instruments of high cabinet in which the dry cell for the potentiometer may precision, the use of which is impractical in an ordinary also be placed. chemical laboratory where fumes and other corrosive subIn operation the pointed tip of the paper-covered gvaalstances are always to be found. Furthermore, these devices nometer needle is adjusted so as to balance on the zero point frequently require complex optical systems, often necessi- on the scale immediately to the right of the slit. The furnace tating a large amount of permanent wall or desk space. temperature is adjusted by variable resistance 10" to 15" The present device has been found highly suitable in higher than that desired. Too high a temperature must be certain catalytic reactions where greater accuracy of tem- avoided, since the lag created drives the galvanometer needle perature control than *0.25" is unnecessary. It is to be completely across the slit, thereby again turning on the recommended for its compactness, efficiency, and com- current. The present device has been tested using a single-junction paratively simple and inexpensive construction. Instead of a mirror galvanometer, it employs a Leeds & Northrup chromel-alumel thermocouple and a well-insulated furnace potentiometer indicator. This type of instrument, it is over a range from 100" to 500" C., and it has been found to true, represents some outlay of money, but is found in most control the temperature to within k 0 . 5 " C. Under the chemical laboratories for the measurement of temperature. same conditions a tri-junction thermocouple increased the Since its use as an auxiliary apparatus does not in any way accuracy to within *0.25" C., which is about the limit of impair its customary utility, its initial cost may be disre- accuracy of the potentiometer used. The accuracy obtained garded, and the cost of the thermoregulator will not be more in any case would also depend upon the lagging of the furnace employed. than $15 to $20. Although the present thermoregulator has been found In the construction of the authors' device, a vertical slit 2 mm. highly suitable in catalytic reactions, it could be used to wide and 8 mm. long is cut through the bottom of the galva- control the temperature of any chemical reaction. Furthernometer of a Leeds & Northrup double-range potentiometer in- more, its range should not be confined to temperatures bedicator, No. 8657C, just to the left of the zero point on the scale. This slit admits light to the compartment ordinarily occu ied tween 100" and 500" C. by a dry cell which is removed to an outside position a n a its ACKNOWLEDGMENT place taken by a photoelectric ceII. A strip of black paper slightly larger than the dimensions of the slit and pointed a t its It is a pleasure to acknowledge the valuable suggestions forward end is pasted on to the galvanometer needle which, with increasin temperature, moves to the left of the zero mark as and assistance rendered by Ralph D. Bennett of the Dethe e. m.?. of the thermocouple rises above that set on the po- partment of Electrical Engineering.
N T H E course of work
March 15, 1935
ANALYTICAL EDITION
LITERATURE CITED Barnes, R. B., and Matosi, F., 2. Physik, 76, 24 (1932). Beattie, J. A., Rev. Sci. Instruments, 2, 458 (1931). Beattie, J. A., and Jacobus, D. D., J . Phus. Chem., 34, 1254 (1930).
Hull, A. W., Gen. Elec. Rev., 32, 213, 390 (1929). Lange, B., and Voos, E., 2. tech. Physik, 15, 323 (1934). Moser, H., Ibid., 13, 383 (1932). Newton, R. H., and Furnas, C. C., Chem. Met. En*,, 39, 455 (1932).
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(8) Roebuck, J. R., Proc. Am. Acad. Arts Sci., 60, 537 (1925). (9) Smith, L. B., Mech. Eno., 48, 153 (1926). (10) Southard, J. C., and Andress, D. H., J . Franklin Inst., 207, 324 (1929). (11) Workman, J. E., Phys. Rev., 37, 1706 (1931). (12) Zabel, R. M., and Hancox, R. R., Rev. Sci. Instruments, 5, 28 (1934). RECEIVIDD December 28, 1934. Contribution No. 118 from the Research Laboratory of Organic Chemistry, Massachusetts Institute of Technology
Determination of Uric Acid in the -Mixed Excrement of Birds JAMESC. FRITZ,Bureau of Animal Industry, U. S. Department of Agriculture, Beltsville, Md.
A
N ACCURATE analysis of the feces is essential for the calculation of digestion coefficients. It is difficult to
obtain the necessary data in the case of birds because the urine and the feces are mixed in the cloaca and excreted together; a method for differentiating the urinary constituents from the fecal constituents present in the mixed excrement is necessary if one is to obtain data for measuring digestibility. In general, the methods used to study digestion in poultry are based on either of two principles. The first is to alter the bird by surgical means so that the urine and the feces are voided separately. The second is to make a chemical estimation of the constituents excreted only in the urine or only in the feces. The protein digestion and metabolism of birds can be studied if we are able to measure the amounts of nitrogen excreted in the forms of uric acid and ammonia, which are the chief end products of nitrogen metabolism in birds. Uric acid is excreted only in the urine. Some ammonia is excreted in the feces, and Katayama (6) introduced a factor t o correct for the small amount which is normally present. Not all the urinary nitrogen is present in the forms of uric acid and ammonia (5-6). Therefore, it is necessary to apply a correction factor to the sum of the uric acid nitrogen and the ammonia nitrogen to obtain the total urinary nitrogen. The various formulas developed to calculate the partition of the excrement nitrogen can be expressed in the following general forms: 1. Fecal nitrogen = excrement nitrogen
4-ammonia nitrogen)
- k (uric acid nitrogen
k is a constant to correct for ammonia nitrogen in the feces and for the urinary nitrogen not present in the forms of uric acid and ammonia. 2. Urinary nitrogen = excrement nitrogen
- fecal nitrogen
Working with Katayama’s data, Titus (11) found that the following modification of Equation 1 gave less variable results than the original form: Fecal nitrogen = 0.9784excrement nitrogen - 1.0253 uric acid nitrogen - 1.2641 excrement ammonia nitrogen - 0.0554 \
\
I n order to use these formulas one needs an accurate method
kor the determination of uric acid in the mixed excrement of fhwls. Several methods, based upon different principles, are reported in the literature. Considerable difficulty was experienced by Brown (W), Bartlett ( I ) , Katayama (4, St. John (7), and other workers who attempted to use the methods previously recorded in the literature. All the methods
give good results when tested on pure uric acid, but are not so rapid and accurate when used on excrement samples. There is a real need for an accurate and convenient method for the determination of uric acid in excrement. The writer has subjected a number of these methods to critical tests with a view to selecting or developing an accurate and rapid technic for the determination of uric acid in the mixed excrement of fowls. The following methods have been studied :I Brown’s isolation and piperidine titration (2). Brown’s method, modified to recover the uric acid gravimetrically instead of titrating it. Katayama’s method for separating the uric acid in the form of ammonium urate, converting it back to the acid form, and then determining nitrogen by the Kjeldahl method (6). Katayama’s method modified for gravimetric recovery of the isolated uric acid. Kionka’s piperidine titration (6). St. John’s method for isolating uric acid (7). Suauki’s method for measuring the amount of ammonia required to convert the uric acid into ammonium urate (IO). Woodman’smethod for isolating uric acid (1.9). The writer’s differential extraction method, which is based on the assumption that acidified water extracts the same nitrogenous constituents, with the exception of uric acid, as does piperidine.
DIFFERENTIAL EXTRACTION METHOD Weigh out two equal samples of the excrement. Two grams make a convenient quantity to handle. To each sample add 20 cc. of a hydrochloric acid solution (5 parts of the concentrated reagent and 95 parts of water), and let the samples stand overnight. This treatment converts urates into free uric acid. Filter, and wash each residue with about 25 cc. of cold water. Transfer the residues, plus the filter papers, t o their respective original beakers. To one of the residues add sufficient piperidine to make the mixture distinctly alkaline to phenolphthalein. Bring the volume to approximately 25 cc. with distilled water. To the other residue add a similar quantity of 0.1 N hydrochloric acid. Digest both mixtures in a water bath at 60’ C. for 1 hour. Filter each mixture through a layer of Celite on a filter cloth (the filter cloth recommended by the Association of Official Agricultural Chemists for use in the determination of crude fiber is satisfactory), and wash the residues with equal quantities of cold wash water. Continue washing until the wash water from the piperidine-extracted material is free from an alkaline reaction. Transfer the residue (and Celite) from the piperidine extraction to a Kjeldahl flask for a total nitrogen determination, A . Transfer the residue (and Celite) from the water extraction t o a second Kjeldahl flask for a total nitrogen determination, B. B - A = uric acid nitrogen Uric acid nitrogen X 3 = urio acid 1 Since this work was completed, another method for determining fecal nitrogen has been reported in the literature. Stotz (8, 9) has described a method for oxidizing uric acid by nitric acid, and washing out the resulting soluble products. After applying suitable corrections, the remaining nitrogen can be considered as fecal nitrogen.
