APRIL 15, 1939
ANALYTICAL EDITION
TABLE11. SIZEOF SAMPLE AS FUNCTION OF COMPOSITION OF ANALYZED MATERIAL AND WEIGHING FORM lOOf is greater than P. Acceptable maximum deviation is chosen as 20%0 of P 7 S w =
P
Type of Determination
f
%
*0.02mg.
MQ.
w =
*0.05mg.
MQ.
K as KzSOa in KHCaHa08 Cu electrolytically in CUSOr.5Hz0 Si02 a8 Si02 in a silicate Ni a8 dimethylglyoxide in steel
20.8 0.449
12
30
25.5 1 30 1 4 0.203
24 18 30
60 45 75
C1 as AgCl in sea water Pasphosphomolybdateinserum
20 0.247 0 . 2 0.016
G./L
Cu. mm.
Cu. mm.
7.5 48
19 120
will occur frequently. Assuming proper manipulative technique, the deviation of the results will be less than nk in more than 99.5 per cent of the determinations, less than l/z n: in more than 80 per cent, and less than ‘/4 n6 in more than 50 per cent of the determinations. The average deviation of a single weighing seems to be a constant of a properly constructed balance and, apparently, does not change unless the instrument is abused or becomes worn out as the natural consequence of years of service. Since the cleaning of a balance is more liable to upset the characteristics of the instrument than any other operation of the normal use, it may be mentioned that Rolf Paulson determined the average deviation of an American balance which had been used by students for 5 years and, during the vacation months, had acquired a coating of dust. Computation of the results of ten weighings furnished an average deviation w = *28 micrograms. Without special care, the balance was then transferred to another floor and underwent a thorough cleaning by the expert hands of Victor Niederl. Finally R. H. Nagel undertook a redetermination of the precision of a weighing and calculated w = *34 micrograms from the results of thirty weighings. The weighings with the balance in question are seriously af-
229
fected by changing the positions of the masses on the pans which is obviously caused by lack of flexibility in the pan suspensions. Nevertheless, the precision appears reproducible within satisfactory limits, if care is taken to simulate closely, in determining the precision, the conditions of actual weighings. Experimental proof of the correctness of the predictions of Table I does not appear necessary. Residue determinations by the author and experiences in the laboratory of J. B. Niederl so far fully support the mathematical deductions.
Literature Cited (1) Benedetti-Pichler, A. A., IND.ENG.C H m f . , Anal. Ed., 8, 373 (1936). (2) Berl, E., and Burkhardt, H., Ber., 59, 890 (1926). (3) Brinton, P. H. M. P., J. Am. Chem. SOC.,41, 1151 (1919). (4) Emich, F., Ber., 43, 29 (1910). (5) Emich, F., and Schneider, F., “Microchemical Laboratory Manual,” p. 56, New York, John Wiley & Sons, 1932. (6) Felgentraeger, W., “Theorie, Konstruktion und Gebrauoh der feineren Hebelwage,” p. 167, Leipsig and Berlin, Teubner, 1907. (7) Gattermann, L., and Wieland, H., “Laboratory Methods of Organic Chemistry,” p. 46, New York, Macmillan Co., 1937. (8) Kuhlmann, W. H. F., private communication, August 20, 1938. (9) Manley, J. J., Proc. Phys. SOC.(London), 38, 473 (1926). (10) Niederl, J. B., and Niederl, V., “Micromethods of Quantitative Organic Elementary Analysis,” p. 14, New York, John Wiley & Sons, 1938. (11) Nieuwenburg, J. van, Mikrochemie, 21, 184 (1936-37). (12) Pregl, F., “Die quantitative Mikroelementaranalvse ornanischer S;bstansen,” -Abderhalden’s Handbuch der -biochemischen Arbeitsmethoden, Vol. 5, p. 1307, Vienna and Berlin, Urban & Schwarzenberg, 1912. (13) Pregl, F., “Die quantitative organische Mikroanalyse,” p. 8, Berlin, Julius Springer, 1930. (14) Pregl, F. (and Lieb, H.), Ibid., p. 173. I t is mentioned that the ammonium phosphomolybdate may be weighed by means of an analytical balance. (15) Sucharda, E., and Bobranski, E., “Halbmikromethoden sur automatischen Verbrennung organischer Substanzen,” p. 1 Braunschweig, Fr. Vieweg, 1929. (16) Wise, L. E., J.Am. Chem. SOC.,39, 2055 (1917).
e.
~
A Modified Pregl Spiral Tube For Sulfur and Halogen Determinations CHARLES W. BEAZLEY, University of Illinois, Urbana, Ill.
T
H E Pregl spiral combustion tube (4) makes it necessary to remove the platinum catalysts before the combustion products can be washed out, and to dry the tube before the catalysts can again be inserted. It was thought that if the tube were cut and a ground-glass joint made of the two parts, one section could be removed to wash o u t t h e products of combustion, and the other retained in the furnace with the platinum catalysts. Such a tube was made and has been used with success in this laboratory. Hallett ( 2 ) has devised a quartz tube which does not have to be removed from the furnace. The time saved using the
tube described in this article is about the same as that saved by the use of Hallett’s apparatus.
Procedure A Pregl spiral combustion tube 640 mm. long is cut 20 mm. from the indenture. A ground-glass joint is made at that point, not by fusing one on, but by grinding on the ends of the two sections. Section B is placed in the split-type electric furnace (Fisher), so that the joint protrudes beyond the end. The sample is then introduced and oxygen admitted. Section A, containing the absorbing medium, is attached to section B without lubricant, and the tube is pulled back so that the ‘oint is inside the furnace. This step ensures collecting the products of combustion in section A. After the combustion, the joint is pushed outside the furnace and left to cool for 2 or 3 minutes. Section A is removed and allowed to cool to room temperature, and the products of combustion are washed out.
The analyses for sulfur were made according to Saschek, (5) but water, instead of hydrogen peroxide, was used as the absorbing medium. Saschek’s technique with the crucible (I), filter stick (3, 6), and small amounts of wash liquid was adapted, for the first time, to the gravimetric determination
INDUSTRIAL AND ENGINEERING CHEMISTRY
230
VOL. 11, NO. 4
TABLEI. TYPICAL RESULTS Sulfur Colcd. Methionine, CsHllOzNS 2-(N-methylamxno)-d-camphane-lO-sulfonio aoid CiiHziOsNS p,p!-D’ibromodiphenyldisulfide, ClnHsBrrSz N-(n-amyl)-m-nitrobenzenesulf onanilide, C1rHzo0aNzS p-Carbethoxyaminobenzenesulf onamide, CsHizOkNzS
Methyl-a-chloro-p-toluate, CeHsOzCl p-Chlorobenzaldehyde, CiHsOCl 5-Chloro-7-nitroisatoic anhydride, CaHsOsNzCl 4-Methylallothreoninebetainehydrochloride, CsHiaOsNCl
Sulfur Found
%
%
20.50
20.46
12.98 17.03
12.95 16.97
9.19
9.22
13.11 Chlorine Calcd. 19.25 25.26 14.64 16.98
l2’ 95 Chlorine Found 19.15 25’ 14’64 16.95
of the halogens. The substitutions made in Saschek’s procedure were as follows: The spiral was moistened with a saturated solution of hydraBine sulfate, dilute nitric acid (1 to 300) was used as the wash liquid, 1 cc. of 5 per cent silver nitrate was used to precipitate the halogen ion, and the crucible containing the filter stick and silver halide was dried at 120° c. from about fifty analyFes made with the tube are reported in Table I.
2-H droxy-4 5,6-trimethoxy-a-chloracetopzenone, diiHisOaC1
l-(4-Bromophenyl)-2,2-diphenylethanol, CzuHnOBr p-Bromoaoetanilide CsHsONBr m-Hydroxy-m’-( 10-bromo-n-decy1oxy)-diphenyl, CzzHaeOzBr
Methyl-3-iodoanisate CeHeOaI o-Iodobenaoic acid, C;HsOd
Chlorine Calcd.
Chlorine Found
%
%
13.55 Bromine Calcd.
13.34 Bromine Found
22.66 37.38
22.70 37.51
19.75 Iodine Calcd. 43.48 51.21
19.91 Iodine Found 43.41 51.04
Literature Cited (1) Benedetti-Pichler, A., 2. anal. Chem., 64, 412 (1924). (2) Hallett, L* T-, IND. ENO.CHEX.9 Anal. Ed-, 10, 101 (1938). (3) Niederl, J., and Niederl, V., “Micromethods of Quantitative Organic Elementary Analysis,” p. 146, New York, John Wiley & Sons, 1938. (4) Roth, H.,“Quantitative Organic Microanalysis of Fritz Pregl,” 3rd ed., p. 95, Philadelphia, Pa., P. Blakiston’s Son and Co., 1937. ( 5 ) Saschek, W., IND. ENO.CHEM.,Anal. Ed., 9, 491 (1937). (6) Schwarz-Bergkampf, E., 2. anal. Chem., 69, 327 (1926).
Apparatus for Microanalysis of Gas C. H. PRESCOTT,
JR., AND JAMES
MORRISON, Bell Telephone Laboratories, New York, N. Y.
This article describes modern refinements of apparatus and technique for the rapid analysis of minute amounts of gas. On samples of 5 to 25 cu. mm. at normal temperature and pressure, analyses may be made with errors for each component within 2 per cent of the total sample. The errors are within 5 per cent on quantities of gas as small as the proverbial limit of 1 cu. mm. The methods described are available for the gases water, carbon dioxide, hydrogen, carbon monoxide, and oxygen or methane. One hour is required for a complete general analysis. Under special conditions the least detectable quantity of a component may be pushed to a limit of 0.025 cu. mm., equivalent to the carbon monoxide in 1 sq. cm. of a monomolecular film.
I
N CONNECTION with contemporary work on the correlation between thermionic activity and the free alkaline earth metal content of an oxide-coated filament (3) the authors have had the problem of assaying extremely small amounts of active metal. This was accomplished by oxidation with carbon dioxide and analysis of the gaseous reaction products, computing active metal from the equivalent carbon monoxide formed. The general methods of analysis are related to conventional vacuum technique, handling the gases a t low pressures over
mercury and solid reagents. The gases are transferred by Toepler pumps, isolated by mercury cutoffs, and measured in a capillary pipet operating in a fashion analogous to a McLeod gage. The detailed apparatus and methods are an extension and refinement of those previously described by one of the authors ( 2 ) . Using this apparatus on a sample of from 1 to 25 cu. mm. a t normal temperature and pressure, a general determination may be made for the components water, carbon dioxide, hydrogen, carbon monoxide, and oxygen or methane, the residual gas being taken as nitrogen. The errors vary from 5 per cent on the smaller samples to 2 per cent on the larger. We may define the error as the difference, between the amount of any one component and the value obtained for this amount by the authors’ method of analysis, divided by the total amount of the sample. I n a general analysis, the least detectable quantity of an individual component is about 0.06 cu. mm. I n simpler analyses, such as on the carbon monoxidecarbon dioxide mixtures encountered in the filament studies, on account of the fewer manipulations required, it was possible to detect a quantity as small as 0.025 cu. mm., or about the amount of carbon monoxide in 1 sq. cm. of a monomolecular film. This sensitivity has been obtained with intentional sacrifice of the accuracy obtainable with former variations of this type of equipment. On apparatus more similar to that previously described (d), with longer mercury columns and larger volumes of reagents, 0.5 per cent accuracy has been obtained on samples of 200 to 400 cu. mm.
Apparatus T h e apparatus is mounted on a rack 1.5 meters ( 5 feet) long and 2.2 meters (7 feet 4 inches) high as shown in Figure 1. T h e glassware, except where specified, is of Pyrex chemical glass throughout.
