Table 1. Results of Determinations of Fluoride Added as Sodium Fluoride Series No.
I
I1
Added 0.950
0.891 0.885 0.467 0.612 0.730 0.940
Fluoride, Mg. Found 0.951, 0.946, 0.959. 0.946,0.940,0.961. 0.940,0.947,0.956, 0.955, 0.942, 0.961 0.895 0.886 0.464 0.609 0.727 0.949
Pipet 5 ml. of this solution into the internal half-cell and 50 ml. into the external half-cell, and check that the e.m.f. of the cell is zero. Pipet a suitable aliquot-e.g., 10 ml. of unknown fluoride-into the internal half-cell and add ten times this volume of distilled water to the external half-cell. With continuous stirring, add standard 0.551
sodium fluoride from the micrcburet until the null-point is obtained. In this example, the quantity of fluoride in the titrant will be approximately ten times the quantity of fluoride in the unknown fluoride sample, the exact value of this factor depending on precise pipet delivery volumes. The factor is usually best determined experimentally by titration against standard 5 x 10-4.11 fluoride. The volumes quoted above are for a typical analysis. Obviously, the size and concentration of the sample for analysis xi11 govern the choice of dimensions of the internal and external half-cells and of the volumes of unknoivn fluoride solution, water, and cerium (1V)-cerium (111) solutions that will be used. The size of the internal half-cell and of the unknown solution used could be reduced considerably. RESULTS
The results of eighteen determinations by this method are shown in Table I. In Series I, the volume of unknown fluoride taken for analysis was 10.00 ml. but in Series I and 11, the volume of
Determination of Carbon by W e t Combustion. Explosives and Initiators SIR: Recently we described a method for determining carbon in alkyldecaboranes based on oxidation in an evacuated apparatus by combustion fluid containing chromic, iodic, phosphoric, and sulfuric acids [ANAL. CHEM.33, 1598 (196l)l. Decomposition was
Table I.
smooth and complete and a n analysis took 1 hour. Dry combustion of these compounds often resulted in violent decomposition unless samples were heated slowly and carefully in oxygen diluted with nitrogen. We have used this met combustion
Determination of Carbon in Explosives and Initiators
Behavior Compound Pentaerythritol tetranitrate Glycerol trinitrate Nitroguanidine 1,ZDinitraminoethane
1,3,5Trinitro-1,3,5-triazacyclohexanc 1,3,5,7-Tetranitro-l,3,5,7-tetraazac~clooctane
Calcd. 19.00 15.87 11.53 16 01 16.22 16.22
Carbon, 7' Found 19.06 15.94 11.48 16.00 16.27
on (3xida-
Diff.
+O.OG $0.07 -0.05 -0.01 +0.05
tion h a h 1
1)
h
2,4,6-Trinitrotoluene 2,4,6-Trinitro-m-xylene 2,4,6-TrinitrophenoI 2,4-Dinitroreaorcinol 4,6-Dinitroresorcinol Lead salt of 2,4-dinitroresorcinol Basic lead salt of 4,6-dinitroresorcinol
37.02 39.84 31.46 36 01 36 01 li.73
16.37 17.68 20.82 36.90 39.83 31.42 36 02 36.20 17.81
[C6H*(NOn)*(OnPb)!alph(OH),l~
12.73
12.74
$0.01
a
18.12
18.06
-0.06
b
1,3-Dinitro-5-nitroso-1,3,5-triazacyclohcxnnr 17.48 1,3,5Trinitroso-l,3,5triaz~cyclohexnnc 20.70
Banum salt of 2,4,6trinitroresorcinol monohydrate
$0.15 +0.20 +o. 12 -0.12 -0.01 -0.04 +0.01
+o. 19 $0.03
b a a a
tl
5 C C
unknown fluoride was varied. For Series 1 and 11, the mean percentage deviations ure 0.7 and 0.45%, respectively. The results quoted here are for solutions 5 X 10-4M in fluoride but results of similar accuracy were obtained for solutions 5 X 10-a~M and 5 x 10-*M in fluoride using these techniques with suitable adjustments of reagent concentrations. Interferences and optimum experimental conditions are the same as for the original method of O'Donnell and Stewart, except that to obtain stable e.ni.f.'S it is better not to reduce the c~eriuni(III)-cerium( llr) concentration below 10-3Alf and, hence, the concentrations quoted for this reagent in this paper are ten times greater than those one would expect by a direct scaling down of the original conditions. T. A. O'DONNELL D. F. STEWART Department of Chemistry University of Melbourne Parkville, N. 2 Victoria, Australia
Application to
method to analyze typical explosive and initiatory substances including nitric esters, nitramines, nitrosamines, nitroaromatic compounds, and lead and barium salts of nitroresorcinols. Even the heavy metal salts of nitroaromatic compounds, for example, barium styphnste, were oxidized safely and rapidly. Of the compounds examined, only tetrazene reacted too violently with combustion fluid to be analyzed by this method. EXPERIMENTAL
The experimental procedure was identical with that described previously apart from the use of combustion fluid containing 5y0 (w./w.) of water for thc analysis of nitramines and nitrosamines. Sample weights of about 0.1 gram were used; only in the analysis of glycerol trinitrate was sand added to the weighed sample. Preliminary experiments were performed to estimate the hazard involved in treating initiators with combustion fluid. Twenty milliliters of the fluid were added to 0.1 gram of the initiator mixed with 1 gram of potassium iodate in a stainless steel beaker placed in a safety screen. RESULTS A N D DISCUSSION
a Reacts readily a t room temperature. b Oxidizes completely below 100' C. c Requires heating to 100" to 200' C. for complete oxidation.
1348
ANALYTICAL CHEMISTRY
The results presented in Table I show that the analyses are usually accurate to better than 0.2% absolute.
The last column in Table I gives an indication of the behavior of each compound toward combustion fluid. I n general, compounds of similar constitution exhibit the same reactivity. The ease of oxidation is dependent on the solubility of the sample in the fluid. Compounds soluble at room temperature usually undergo oxidation immediately, although gentle warming is sometimes necessary to increase the rate of decomposition. Less soluble compounds are dissolved and oxidized by more vigorous heating. Initiators behave similarly to the nitroresorcinols from which they are derived; decompositions proceed smoothly at a low temperature. TetraBene fumes and tends to explode in contact with combustion fluid. It seems likely that the analysis of tetrazene by wet or dry combustion is
particularly difficult because of the low ignition temperature of the compound (about 130" C.) compared with those of the lead and barium salts of nitroresorcinols (230" to 250' C.). Low values are obtained for the carbon content of 1,3,5-trinitro-l,3,5triazacyclohexane (RDX) if the usual combustion fluid is used. Attempts to increase the efficiency of oxidation by using finely ground or reprecipitated R D X result in even lower values. Improved results are obtained by heating the reaction mixture rapidly but agreement is still unsatisfactory. These observations confirm earlier work [Farrington, P. S., Niemann, C., Swift, F,.H., ANAL. CREW 21, 1423 (1949)] which showed that compounds capable of forming hydrogen cyanide on decomposition frequently gave low values for carbon by wet combustion. As hydrogen
cyanide is known to undergo hydrolysis in strong sulfuric acid we decided to dilute the usual combustion fluid with water. Entirely satisfactory results are obtained when the wet combustion of RDX and other nitramines and nitrosamines is performed using combustion fluid containing 5% (w./w.) of water. ACKNOWLEDGMENT
The authors are indebted to G. W. C. Taylor and J. R. White for advice and assistance in the analysis of initiators. IVAN DUNSTAN JOHN v. GRIFFITHS
Ex losives Research and Development 8stablishment Ministry of Aviation Waltham Abbey Esaex, England
Partition of Pertechnetate Ion in Nitric Acid with Diethyl Ether One ml. of copper solution (3.0 mg./ml.) was added as a precipitating carrier. (The sulfide of copper is considered to be among one of the best carriers for technetium in sulfide precipitations.) Both were simultaneously heated in a water bavh and H$ waa passed through for the same length of time and cooled for the same length of time before filtering. The samples were filtered on glass fiber filter paper, mounted on stainless steel planchets, and counted. The extraction coefficient is defined as
SIR: In this laboratory it was necessary to obtain information of the partition behavior of tracer quantities of heptavalent technetium as TcOl- in nitric acid concentrations with diethyl ether. Boyd and Larson (1) have completed an excellent survey of the extractibility of technetium into various organic solvents. They reported the distribution coefficient for the pertechnetate ion 1 N HnSO4 to be 0.029. Morgan and Sizeland (3) have shown that pertechnetate ion extracts into ether from nitric acid normalities of 0.0 to 4.0, whereas Gerlit (8) reported no extractibility of pertechnetate into ether from 2N H2S0,. EXPERIMENTAL
Apparatus and Reagents. All reagents used in this work were of the highest grade obtainable, usually Reagent ACS purity, which included diethyl ether, hydrogen sulfide, nitric acid, and copper wire. Technetium-99 (TI/? = 2.15 x 106 years) (Oak Ridge National Laboratory, Oak Ridge, Tenn.) in the form of ammonium pertechnetate was used as the radioactive tracer. The purity was about 99.5%. Proper amounts were used to yield solutions containing about 250 d.p.m. per ml. A Tracerlab SC-90 utility scaler equipped with a Tracerlab TGC-2/1B84 Geiger tube housed in a Tracerlab manual sample changer WM used for counting. (Background averaged about 18 c.p.m.) Procedure. Partition of the pertechnetate anion into diethyl ether
E9 =
v.
activity in the organic layer (1) activity in the aqueous layer ' V , Close temperature control was not necessary for the extraction condition Figure 1. Variation of the extraction coefficient of TcO4- with ni':ic acid ~~~
was investigated in the following manner: I n a 125-ml. separatory funnel 4.0 ml. of pertechnetate solution (about 1 X 10s d.p.m.) and a proper amount of nitric acid and distilled water were added to obtain a volume of 10.0 ml. of desired normality of nitric acid. 10.0 ml. of diethyl ether was added, and the two components were vigorously shaken and allowed to equilibrate. After complete separation, the aqueous layer was drawn off into one beaker. The ether layer was backextracted with three portions of 15 ml. of distilled water and all collected into another beaker. Each fraction was made 2N with nitric acid with a total volume of approximately 100 ml.
~
Table 1. Extraction Coefficients of Tc04- in HNOI Media with Diethyl Ether Initial "0, N Extraction in Aqueous Phase Coefficient 0.0 0.016 0,029 0.5 0.047 1.0 0,068 1.5 2.0 0.087 0,094 2.5 3.0 0.244 3.5 0,271 4.0 0.413 4.5 0.408 5.0 0.705 6.0 0.906 8.0 1,267 10.0 1.098
VOL. 34, NO. 10, SEPTEMBER 1962
1349
