V O L U M E 28, NO. 7, J U L Y 1 9 5 6 Table VII,
Cupellation of Lead-Platinurn Buttons
Pt Taken,
Bead Size,
Y
25
Mg. 10
100
500 1000
1193
(25-gram lead button) Platinum Found, y In In Difference, bead cupel Total Y 23
25 22
1 0 1
24
10
100
75 250
98 97 485 487 500
0 0
100 98 98
0 2 2
16
A 1 1
965 981 965
33 20 22
501 499 500 998
75 250
10
75 250
10
75 250
1
12 0
2: 23
1001 Q8i
1 0
2
0 2 + I 13
CUPELLATION OF LEAD-PLATINL31 BUTTONS
Cupellation is the common process for the rapid determination of platinum in lead buttons. Palladium was the only one of the platinum metals investigated which was not subject to serious losses during cupellation. As the silver-platinum alloy forms readily, large losses were not expected to occur. The authors present below data on the behavior of platiniim diiring cupellation. Preparation of Lead Buttons. A cup-shaped oontainer was made from a 5 X 5 inch square of lead foil, 0.005 inch thick. Varying amounts of standard platinum solution were added and evaporated to dryness in a steam cabinet. Weighed amounts of silver powder were added and the lead foil was carefully formed into a ball and wrapped with a 2 X 4 inch piece of lead foil. Synthetic lead buttons were made by high compression of the lead foil in a steel mold. Procedure. The buttons were placed in the furnac~eon preheated bone ash cupels a t a temperature of 900" C. and left until the lead was removed and the silver beads had formed. Parting in sulfuric acid and estimation of platinum were made as described above. S o trace of platinum was found in the sulfuric acid parting solution by the method described above. Assay of Cupels. The used cupel was assayed to determine whether any mechanical or absorption losses of platinum had occurred. The stained part only was weighed and ground in a mortar to pass a S o . 45 standard sieve. The following additions were made to flux the stained bone ash: 3 / 1 of its weight of soda ash, of its weight of borax glass, '/4 of its weight of calcium fluoride, of its weight of silica sand, and excess flour ( 4 grams). These siihstanres were intimately mixed hy rolling on a cellophane shert and were placed in an assay crucihl(,. Fusion tem-
peratures were 1000 to 11.10" C. The lead button wa8 parted in nitric arid (1 to 4) and platinum !vas determined colorimetrically. Comparisons were made with a standard c-urve prepared by assay of ciipels stained by cupelling salted lead foil without added silver. Table VI1 indicates that no significant losses of platinum occurred during cupellation. Difference in the bead size did not appear to be an important variable, but larger losses to the cupel were recorded when the ratio of platinuni to silver was reduced to 20 to 1 and 10 to 1. The results x i t h these small beads (10 mg.) are of interest because they are used in spectrographic determinations of the platinum metals in ores and concentrates, CONCLUSION s
The distribution of platinum during the various processes involved in a fire assay has been examined. Acceptable over-all recoveries were obtained except where the slags contained considerable nickel. ru'early complete recovery \vas obtained with only one reassay. except xvith acid fluxes, where high silica content tended to hinder the collection. Pot wall loss may be a major reason for the small amounts of platinum not recovered in normal fire assaying. Serious loss of platinum to the nitric acid parting solution \T-as experienced in some cases. Cupellation losses with platinum were not significant. 4CKIVOW LEDG%IE\T
Apprcclatiori is expressed to the Canadian Department of Agriculture. Science Service. for hnancial .tipport and leave of absence given to I. Hoffman LITERATURE CITED
(1) d l i a n , IT.J.. Beamish. F. E.. .Is.%[.. CHEM.24, 15-09 (1952). (2) Allen, 1%'. F., Beamish, F. E., [ h i d . , 22, 451 (195U). (3) Ayres, G. H., Meyer, A. S...Jr.. I b i d . . 23, 209 (1951). (4) Barefoot, R . R . , Beamish, F. E., Ibid., 24, 8.10 (1952). (5) Currah, J. E., N c B r y d e , W.A. E., Cruikshank. d.J.. Beamish. F. E.. IND.EXG.CHEM..a % ~ . k ~I.D. ,. 18, 120 (194ij), (6) D e Trecco, Della Rubini. Rei. a s i c . Liopuim. argenti, a 15, 355 (1951). (7) Fraser, J. G., Beamish, F. E., - 4 s ~CHEM. ~ . 26, 1474 (1954). (8) Gilchrist, E., J . Research S a t l . Bur. Standards 30, 89 (1943). (9) Hampel; C. -I., "Rare Metals Handbook," p. 292, Reinhold, S e w l o r k , 1954. (10) Thiers, R . . G r a y d o n , K., Beamish. F. E . , .IN.~I.. CHEY.20, 831 (1946), RECEIT-EI) f o r rmieis- December 22. 1953.
Accepted ?+larch5 ? 1950.
Modified Micro-Du mas Proeedure for Determining Nitrogen C. E. CHILDS, E. E. MEYERS, C. K. JOHNSTON, and J. D. MlTULSKl Research Laboratories, Parke, Davis & Co., Detroit, M i c h .
A modified Dumas procedure has been developed in which the small movable burner is replaced by a regular furnace. The advantages are: more complete combustion, a shorter burning time, and a minimum of handling by the operator.
R
E C E S T improvements in the Dumas method for the microdetermination of nitrogen in organic compounds have included the use of nickel oxide, high temperatures, oxygen, mixing chambers, etc. (1, 3-5). Another modification, developed in this laboratory, substitutes a micro romhustion furnace for the movable burner.
EQUIPMENT
From left t o right the apparatus consists of the usual riitmnieter, ttvo -4.H . Thomas Co. micro combustion hinged-front furnaces (Catalog No. 5678-A) on a slightly enlarged stand with the stationary furnace on the left and the burner furnace on the right, and a Poth-type carbon dioxide generator ( 2 ) . A standard Vycor combustion tube is used with a permanent filling of copper oxide, reduced copper, and copper oxide, in that order. The stationary furnace covers the permanent filling. The temporary filling, 11-hichincludes the mixture of fine copper oxide and sample, is added to the tube so that the sample is located in the area to the left of the center of the burner furnace-that is, it should be enclosed within 4 to 10 cm. of the left end of the burner furnace; otherivise, the unburned sample might possibly sublime away from the heat. The tube is then placed on the stand so that it extends 5 cm. beyond the edge of the stand towards the nitrom-
1194
ANA Table I.
% Theory
CompoundQ
8.09
Acetanilide
10.36
Nicotinic acid
11.35
Cystine
11.66
Benaylisothidiirea €IC1
13.82
Azobenzene
15.38
2,4-Bis(benzylarnino)B,7-diphenylpteridine
1fi.99
4-(4-hlorpholinyl)-f,7-diphenplpteridine
18.96
p-Carboxyphenylazobarbituric acid
20.30
2,4-Bis(3-diethylaminopropylamino)-6,7-diphenylpteridine
20.72
2,4-Bis(2-hydroxyetliylamino)6,7-diphenylpteridine 20 88
Sulfadiazine
22 39
2,4-Bis-allylainino-G-(p-c hloroani1ino)-8-triazine
26.61
Arginine HCI
26 60
2,4-Diamino-6,i-diphenylpteridine
2fi, 74
Tetramethyldipyrimidopyrazinetetrone
27,62
4-Amino-6-hydroxy-5-nitropyrimidine
35.90
Thioguanine
41,92
a
flushed out with carbon dioxide for a few minutes. The stationary furnace is pulled over the permanent filling and when microbubbles are obtained, the carbon dioxide is stopped. The burner furnace is slowly drawn from the side across the tube over the temporary filling, depending upon the bubble rate (not more than 3 per second), and finally placed entirely over the tube and butted against the stationary furnace. When the bubble rate diminishes to 1 every 5 seconds, the carbon dioxide is turned on and the bubble rate is adjusted t o 4 per second. The furnaces remain in position until near-microbubbles appear, then are moved back. When microbubbles are obtained, the determination is complete. The time taken for an analysis usually runs between 15 and 20 minutes.
Nitrogen Determinations
Sulfanilic acid
% Found 8.06 8.13 10.35 10.61 11.35 1- -1. - xn _ 11.46 11.52 13.88 14.03 15.37 15.40 17.11 16.96 19.00 18 83 20 45 20 32 20.76 20.60 20.90 20 96 22.28 22.34 26,89 2 6 . til 26 62 26,74 26 80 2 6 . 79 27.54 27.57 36.03 35.90 42.23 41 94
Sample weights between 3 and 5 mg.
eter. The furnace temperatures are close to 675' C. for the stationary furnace, and 725" C. for the burner furnace. If numerous halogen or sulfur compounds are run, the tube should be burned out or replaced. Old used tubes should be discarded. PROCEDURE
A modified Dumas procedure is used. The combustion tube is connected to the nitrometer and the carbon dioxide source and
L Y TICA L C H E MI6 T R Y
DISCUSSION AND RESULTS
This particular modification was developed after considerable experimentation with various high temperature movable burners, etc. The advantages that appeared were several: more complete combustion, a shorter burning time, and a minimum of handling by the operator. There is no need for reburning, a8 the furnace covers the entire sample and temporary filling. There is less possibility of burning the sample too fast, thereby having incomplete combustion, because the whole tube is maintained a t a rather high temperature. Once the furnaces are in placethat is, over the tube-the apparatus requires very little attention. It is simply a matter of adjusting the carbon dioxide flow and terminating the procedure when microbubbles appear. To test the efficiency of this modification a variety of compounds were analyzed, as shown in Table I. In addition, hundreds of routine samples have been run with very good resiilts. LITERQTURE CITED
(1) Alford W. C., Ax.4~. CHEY.24,881 (1952). (2) Childs, C. E., Moore, V. A . Ibid., 25, 204 (1953) (3) Gysel, H., Helv. Chiin. Acta 35, 802 (1952). (4) Kirsten, W., A N A ICHEM. . 25,74 (1953). (5) Shelberg, E. F.. Ibid., 23, 1492 (1951). RECEIVED for review Septemher 30, 1955. Accepted March 21, 1956.
Infrared Absorption Spectra of Branched-Chain Fatty Acids DONALD L. GUERTIN, STEPHEN E. WIBERLEY, Department
o f Chemistry,
and
WALTER H. BAUER
Rensselaer Polytechnic Institute, Tioy,
N. Y.
and
JEROME GOLDENSON Chemical Corps Chemical a n d Radiological Laboratories, A r m y Chemical Center,
From a study of the infrared absorption spectra of long branched-chain fatty acids Freeman has shown that the relative intensities of the bands at 7.8 and 8.1 microns are valuable in identifying a-substitution. This correlation holds for the branched-chain hexanoic acids. In addition, the relative intensities of the bands at 6.8 and 7.1 microns are valuable in identifying a-substitution in acids containing less than 14 carbon atoms.
F
REEMAN ( 1 ) in his study of the infrared spectra of 27
branched long-chain fatty acids found that the relative intensities of the absorption bands near 7.8 and 8.1 microns could be used to distinguish fatty acids with a branched-chain in the a-position. The band a t 7.8 microns was the stronger of the two, except when a group was substituted in the a-position.
Md.
To see whether this correlation would hold for the branched short-chain fatty acids, the spectra of 15 such acids were measured on a Perkin Elmer Model 21 double-beam recording infrared spectrometer equipped a i t h rock salt optics. The liquid acids were run in a demountable liquid cell without dilution. No spacer was employed. The fatty acids vere synthesized by the Bureau of Mines and were obtained from the Chemical Corps Chemical and Radiological Laboratories. The position of branching was determined by the method of synthesis. Carbon-hydrogen analysis and neutralization equivalents were reported. Agreement between the calculated and experimental values was excellent. Freezing point data were used to determine mole per cent purity in several cases. The 2-isopropyl; 2-n-butyl-, 3-n-propyl-, 4-ethy1-, and 5-methylhexanoic acids were better than 95 mole % pure. T h e 2-ethyl- and 3-methylhexanoic acids were, respectively, 92 and 89% pure. The spectra of these acids in the region of 6.5 to 8.5 microns are plotted in Figure 1. It is apparent from this figure that the
