ANALYTICAL CHEMISTRY
668 From the equivalent weights determined by these analyses and also from the known reactants and conditions present in the original reaction mixture, the identity of the two materials was ePtablished as HC=CCH( OCH& and H2C(OCH,C=CH)2. For HC=CCH( OCH3)2, the functional group analysis not only indicated what groups were present and which of the starting groups were absent, but yielded the equivalent weight according to each group. This showed that there was one acetylenic hydrogen for each acetal-like group, and that there was either one triple bond for each of the above groups or two double bonds. Then, assunling the molecular weight of the compound equal to the equivalent weight, the formula was reached. From the knowledge of the system, it was known that propargyl alcohol, the desired product of the reaction, oxidizes on standing to the corresponding aldehyde. Also it was known that methanol was present in the formalin used in the synthesis. The reaction mixture was also slightly acidic; thus, there were all the prerequisites to obtain the compound indicated by the functional group determination. For H2C(OCH2C=CH)2, again the functional group determination indicated the groups present and which of the starting groupq were absent. The equivalent weight according to each group indicated that two acetylenic hydrogens were present for each acetal-like group and also that there were two triple bonds (or an unlikely four double bonds) for each acetal-like group. It was evident then that the molecular weight was at least the equivalent weight as calculated from the acetal analysis with two acetylenic hydrogens and two triple bonds, or that the molecular weight had t o be some multiple of that value. From these data and from the fact that it was knov n that formaldehyde and propargyl alcohol were present in the original reaction and that they form
formals under slightly acid conditions (which were present in the reaction) the identity of the compound was arrived at. Functional group determination does not make an absolute identification. It does, however, yield data which serve to indicate the probable identity of the compound. The absolut'e identification is made by act,ually synthesizing by known methods the compound indicated by the funct,ional group determination and then comparing the known against the unknown by st,andard techniques such,as comparison of the infrared curves of each, the x-ray diffract,ion patterns in the case of cryst,alline solids, and microscopical examination for crystalline solids in order to compare crystalline form, refractive indexes, and other optical behavior. Other physical properties such as boiling point, freezing point, refractive index, and density can be used to compare the known and the unknovm. Quantitative detr~rminatiori of the functional groups can be a valuable aid in identifying complete unknowns as well as in verifying the identity of suspected compounds. I n the latter type of identification, the functional group determination, because of its specificity, yields a more meaningful idrntification than does an elenirantal analysis. The main value of functional group analysis in identifying complete unknowns is in determining the ratio of the groups t,o one another and determining the functional equivalent weight of the compound, a factor in the molecular weight. RECEIVEDJuly 25, 19.50.
Determination of Microgram Amounts of Calcium and Magnesium in Vanadium Metal JOSEPH RYNASIEWICZ, RVTH GUENTHER, M. E. SLEEPER, ~ V R. D H. GALE Knolls .Itomic Power Laboratory, General Electric Co., Schenectady, .V. Y . method of preparing high-purity vanadium metal to 0SEreduce vanadium pentoxide with calcium in a vessel someis
times lined with magnesia. Saturally, calcium and magnesium were suspected as major impurities in vanadium, but no suitable method of analysis could be found to verify this belief. Accordingly, this laboratory has developed a method for the determination of microgram quantitieq of calcium and magnesium in vanadium. The precipitation of small amounts of calcium as calcium oxalate in a thousandfold excess of vanadium was not feasible. It has been reported (3, 6) that calcium cannot be determined as oxalate in solutions of high ionic strength because of the large solubility of calcium oxalate under these conditions, and because of the coprecipitation of other constituents in the solution. Therefore, it was necessary to separate the calcium from vanadium, before the calcium could be determined microvolumetrically. Vanadium was separated from calcium with cupferron, the classical reagent reviewed b y Furinan and coworkers ( 1 ) . According t o the procedure described hy Guenther and Gale ( 2 ) , vanadiuni was precipitated from a n acid solution with cupferron and the cupferride was then extracted with chloroform. Calcium and magnesium were determined in the aqueous phase as calcium oxalate and as magnesium ammonium phosphate according to the method described by Marsden ( 4 ) . PROCEDURE
Dissolve as small a sample as possible up to 1 ram of vanadium metal (contrtining 0.1 to 5 mg. of calcium a n 3 0.1 to 2 mg. of magnesium) in 30 ml. of 1 to 1 nitric acid, evaporate the solution to dryness several times with hydrochloric acid, and take u p the vanadium chloride with 30 ml.'of 10% hydrochloric acid. Cool the vanadium solution, the cupferron solution, and a bottle of wash water in an ice bath. Transfer the vanadium solution to a 125-ml. separatory funnel, add 15 ml. of cold 5y0 cupferron solu-
tion, shake for 2' nliriutes, and extract the cupferride with 50 in1 of chloroform. Repeat the cupferride precipitation and extraction until the vanadium has been removed. About four or five extractions are necessary to remove 0.5 gram of vanadium. Test for the presence of any unextracted vanadium with a few drops of cupferron solution. A milky white precipitate, instead of thr brown vanadium cupferride, indicates adequate removal of vanadium. Kithdraw the a ueous phase into a 250-ml. beaker, evaporate the solution to %yness, and destroy any residual organic matter by repeated evaporation with nitric and hydrochloric acids. Dissolve the residue in 20 ml. of water plus a few drops of hydrochloric acid. Reflux the solution in the covered vessel, and transfer it to a 50-ml. beaker. At this point the volume should not be greater than 20 in]. Determine calcium and magnesium as previously described ( G , 6). RESULTS
Tables I and 11 show the recoveries of microgram amounts of calcium and magnesium from solutions containing 1 gram of vanadium as vanadium chloride. The extraction of vanadium was done in 10% sulfuric acid as well as in hydrochloric acid, but this lengthened the procedure because of the increape in time necessary to evaporate the sulfuric
Table I. Recoveries of Calcium from Vanadium Chloride Solutionsa by t h e Cupferron-Oxalate Method Calcium .4d=
Calcium Recoveredb
Mg.
7c
0.09
0.009 0.018 0.028 0.037
0.18 0.28 0.37
Mg. 0.06 0.17 0.26 0.36
% 0.006 0.017 0.026 0.036
Each solution contained vanadium chloride equivalent t o 1 gram of vanadium. b A value of 0.20 mg. for calcium in reagents and C.P. vanadium chloride was subtracted.
V O L U M E 23, NO. 4, A P R I L 1 9 5 1 Table 11.
669
Recoveries of Calcium and Magnesium from Same V a n a d i u m Chloride Solution" Caloium
Calcium Added
Recovered
% 0.09 0.018 0.28 0.056 0.46 0.092
MagneSium Added
hIBK"e8ium
Recovered % ..
5%
Mo. i ? n 0.13 0.026 0 . 1 2 (1.024 0.13 0.28 0.056 0 . 2 4 0.048 0.21 0.48 0.096 0.36 0.072 0.38 0 0 0.02 0.004 0 0 0 Each solution contained vanadium chloride equivalent to 0.5 vanadium. The vanadium chloride w e d TV&S a purer made than ported in Table I. MQ.
1%.
Nine different vanadium samples, prepared by the calcium bomb reduction method, were analyzed by the nroeedure described and contained 0.01 to 0.06% calcium
.
~
0.026 0,042
0.076
0 that
ACKNOWLEDGMENT
T h e vanwlium samples were prepared by It. K. IMcKechnle in the l\letallurgiesl Division of this laboratory. The authors wish to thank I,. P. P e p k o u h tar reviewing the manuscript.
=~. LITERATURE CmED
acid to dryness. A complete separation of vanadium from calcium was not necessary before analyzing calcium microvolumetrioblly by the described method, as 0.5 mg. of calcium could he determined in the presence of ten times 88 much vanadium without a separation. The amount of unextractahle vanadium is usually less than 1 mg. Several attempts were made to determine 0.5 mg. of calcium in the presence of ahout 50 mg. of vanadium without a cupferron separation, but difficulty was encountered in precipitating the small amounts of calcium a t a p H of 4 under these conditions.
(1) Furman, N. H.. Mason. R . B.. and Pekola, J. S., ANIL. CEEM., 21, 1325 (1949). (2) Guenther. R . , and Gale. R . H.. Knolls Atomic Power Laboratory. K A P L Rept. 262 (1949). (3) Mslisroff, K. L., and Gluschakoff, A. J., Z.anal. Chem., 93, 265 (1933). (4) Marsden. A. IT.,J . Soc. Chom. Ind.,60,21 (1941). ( 5 ) Rynasiewicz. J.. and Pollcy. M. E., ANAL. C~BM.. 21. 1398
(1949). Rscerveo July 10, 1950. The Knolls Atomic Power Laboratory is operated by the General Electric Researoh Laboratory for the Atomio Energy Commission. The work reported here waa oarried out under contract No. W-31109 Eng.-52
Modification of Lamp Method for Sulfur in Naphthalene J. J. TIGHE, J. S. MCNULTY, ,kND E. J . CENTER Battelle Memorial Institute,4Columbus, Ohio
HE quantitative determination of small amounts of sulfur in Tnaphthalene has presented numerous difficulties. A combustion procedure has been suggested by Hinckley (5). This method involves considerable apparatus and reouires close attention during the burning ofthe sample. Table I. Shmple NO.
Method
Precision and Accuracy Sample Weight
Mv. Parr bomb (peroxide)
236 264 264' ~.
Sulfur' Added
S"liW Found
%
I%?.
..
.. ..
0.610 0.603
..
0.599
0 603
GTOma
Lamp
5 . 1I4
5.130 2
Lamp
:
.
0.596 Mo. 5.20b
"
"".%
3.09
14.1 17.0
15.9 14.9 17.9
3.06 3.08
20.3
4.50
..
3.14
3.15
Lamp
5.25
E" " i ""
5.L.
2
..
5.00
Added as elemental sulfur. b Correoted for sulfur present in naDhthaiene.
15.3 19.4
Cn
18.6
20.3
0.0016 0 0015
T h e A.S.T.M. lamp method (Z) is spplkable to the determination of sulfur in any liquid that can be burned completely in a wick l a m p i . e . , gasoline, kerosene, etc. An attempted application of this lamp method for solid materials has been reported (5). Hinckley, Wilson et ai., rejected the lamp combustion of solutions of naphthalene because of the deposition of naphthalene on the cooler portions of the wick and the difficulty of obtaining s sootless flame. The low solubility of naphthalene a t room temperature in oxygen-containing solvents (4.18 grams per 100 grams of ethyl alcohol a t 20" C.) also results in a long combustion time whenever a large sample weight must he used. The use of %n infrared lamp to overcome these difficulties in the lamp method is descrihed helow.
A commercial lamp (Westinghouse Heat-Ray) is mounted in a flexible stand 8 t o 10 inches from the sample and wick, and the beam is directed upon the sample container and the wick holder (Fi,pre 1). A temperature of 50" to 60" C. is readily obtainable mside the apparatus. At this temperature, the solubility of the naphthalene 1s i n o r e a d t o 25 to 30% in ethyl alcohol, and the combustian time is thus not excessive. (Five grams may be burned in 0 t o 8 hours.) The higher temperature of the wick also maintains the solution of the naphthalene and prevents clogging of the wick and tube by solid naphthalene. As in the A.S.T.M. procedure for use of a diluent, two additions of the solvent are made when the combustion is nearly completed, to flush the sample holder and to ensure complete combustion of the naphthalene. In a permanent apparatus, a side arm with R
