I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
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Vol. 15, No. 10
The Freezing Point-Solubility Diagram of the System Tet ry 1-Pi cri c Acid' By C. A. Taylor and William H. Rinkenbach BUREAUOF MINES,PITTSBURGH, PA.
H E freezing point curves of the binary systems of TXT-tetry12 and TNT-picric acid3 have previously been determined by the writers, and the freezing point curve of tetryl-picric acid, as herein discussed, completes the series. The method, apparatus used, and the purification of the materials employed in this work have been described in detail in the articles mentioned. The tetryl had a setting point of 128.72' C., and that of the picric acid was 121.9' C. Each was melted and cooled before being used. Considerable difficulty was encountered in obtaining accurate check results on the same mixture in the course of the work on mixtures of tetryl and picric acid. This difficulty was found to be due to a tendency on the part of these mixtures to supercool to a remarkable degree. For example, a melt containing 50 per cent of each component cooled to room temperature without the formation of a solid phase. The cold, extremely viscous liquid so obtained remained in this state for about 10 days, although the forcing of crystallization by means of "seeding" was attempted, and it then solidified very slowly. Another melt that was constantly agitated supercooled to room temperature, began to solidify slowly after 2 hours, and caused a rise in temperature of only 2 degrees.
T
--MOLECULAR Picric Tetryl Acid
0.00 15.00 30.00 40.00 45.00 47.50 50.00 52.50 55.00 58.00 60.00 62.00 65.00 70.00 77.14 88.12 90.00 100.00
100.00 85,OO 70,OO 60.00 55.00 52.50 50.00 47.50 45.00 42.00 40.00 38.00 35.00 30.00 22.86 11.88 10.00 0.00
PERCENTAGE OF Tetryl 0.00
12.34 25.48 34.72 39.50 41.92 44.38 46.86 49.43 62.42 54,48 56,56 59.71 65.05 72.92 85.14 87,7S 100.00
7
Picric Acid
100.00 87.66 74.52 66.28 60.50 58.08 55.62 53.14 50.57 47.58 45.52 43.45 40.29 34.95 27.08 14.86 12.22 0.00
Cooling Points Found Average C.
121.8 111.75 99.9 90.0 84.8 81.05 76.65 72.2
....
77.3 81.0 84.2 90.1 98.3 108.9 120.2 121.75 128 72 I
acid. Curves showing the lowering of the melting points of the pure components in the usual way are obtained except in mixtures containing 44 to 63 per cent tetryl. A melt containing 50 per cent of each component, for example, gave a cooling curve of the type shown in Fig. 2. The maximum temperature attained (d in Fig. 2 ) varied in individual cases from 75.6' to 81.9" C. When this same mixture was allowed to solidify and was then slowly heated, a curve (Fig. 3) indicating a melting point of 85.5' C. was obtained. The other mixtures within this concentration range gave similar results.
Melting Point
c.
FIG.
....
FREEZING POINTCURVEOF TETRYLAND PICRICA C ~ D
....
85.6
82
85.5 85.5 85.5
80
....
....
84.6
I8
.... ....
Q
.... ....
53 I4
....
In addition to the use of cooling curves for the derivation of equilibrium data, it was found advisable to employ heating curves. These were obtained by gradually heating the previously cooled melt in the apparatus used for cooling curve work, the temperature of the bath being slightly higher than that necessary for the formation of a homogeneous solution. The rise in temperature of the melt was steady until the saturation temperature was reached, when there was a period during which the temperature of the melt remained constant. The results obtained by the use of both cooling and heating curves are shown in the table and in Fig. 1.
INTERPRETATION OF RESULTS Inspection of the curve derived from the foregoing data shows a different type than TNT-tetryl and TNT-picric 1 Received May 1, 1923. Published by permission of the Director, U . S. Bureau of Mines. *THISJOURNAL,16, 73 (1923). 8 I b i d . , 16, 795 (1923).
2 16
72 70 68
TIME OF COOLING, SECONDS
FIG. C COOLING CURVEOF MIXTUREOF TETRYL AND PICRICACID
Plotting these results (Fig. l),we have a curve indicating the formation of a compound of the components. However, on account of the great tendency on the part of this compound to supercool, as previously shown, it was possible to complete the curve on both branches through the metastable condition. COMPOSITION OF CONPOUND FORMED Calculation shows that the percentage composition of the simple compounds usually formed in such cases is as follows: 1 molecule tetryl : 2 molecules picric acid 1 molecule tetryl : 1 molecule picric acid 2 molecules tetryl : 1 molecule picric acid
38.52 per cent tetryl 86.62 per cent tetryl 71.47 per cent tetryl
October, 1923
I N D U S T R I A L A N D ENGINEERING CHEMISTRY
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Bureau of Mines, Pittsburgh, Pa., for examination. He found that there was a third substance present in the melts, but owing to the high refractive indices of all the substances, it was not possible to make quantitative comparisons.
APPLICATION OF THE DATA The data can be applied to the analysis of mixtures of tetryl and picric acid in the manner described in the paper dealing with mixtures of T X T and tetryl.2 However, it is difficult to use this method within the concentration range 44 to 63 per cent of tetryl, because of the difficulty in obtaining accurate checks and the peculiarities of this portion of the curve. The difficulty in obtaining accurate checks may be ascribed to the fact that the supercooled mixtures 4 are rather viscous. Thick suspension of air bubbles is quickly TIME OF HEATING, MINUTES formed when the melt is stirred, and this prevents an even FIG.8 - c U R V E SHOWING RISEI N TEMPERATURE AS MIXTURES OF TETRYL rate of heat transference, so that the uneven rate of cooling AND PICRIC ACIDARE HEATEDAT UNIFORM RATES under the best of conditions yields results that are not within the usual range of accuracy. From this it would appear that the compound formed conACKNOWLEDGMENT sists of one molecule of tetryl and one molecule of picric The writers wish to express their appreciation of the many acid, as the others are outside the concentration range covered helpful suggestions on the interpretation of the data given by the flat portion of the curve. Melts of the pure components and various melts of these by R. E. Hall, physical chemist of the Pittsburgh Experitwo were submitted to W. M. Myer, petrographer of the ment Station, Bureau of Mines.
T h e Separation of Tin from Other Metals’ Including Its Determination after Precipitation by Means of Cupferron By N. Howell Furman PRINCETON UNIVERSITY, PRINCETON, N. J.
Kling and Lassieur haae proposed the use of cupferron as a precipitant for quadritralent tin. This method has been studied in detail, and found to be rapid, conaenient. and accurate. I t is especially suitable in connection with the analysis of tin-antimony alloys by the McCay method. A n alternate electrolytic method which Kling and Lassieur recommend highly has not been found to be satisfactory for the rapid determination of tin.
Attention has been called to a widespread serious misunderstanding of the conditions which are necessary for the separation of antimony from tin in dilute hydroj7uoric acid solutions. B y means of established methods, together with some additional ones here described, tin may be separated from copper, lead, arsenic, antimony, bismuth, cadmium, zinc. manganese, cobalt, and nickel.
EARLY all the metallic elements which are commonly
conditions recommended by McCay5 in liis scheme for the analysis of the tin-antimony alloys, no zinc is precipitated with the copper sulfide. This detail is being studied further. McCay has proposed a simple and accurate method for the analysis of the tin-antimony alloys, which is based upon his excellent method for the separation of antimony from tinS4s5The only criticism of the original method of which the author is aware was directed toward the necessity of using a platinum dish to remove the hydrogen fluoride before a determination of tin could be made. It was later shown by the author that the fluorine can be removed from the sphere of action by the addition of a large excess of boric acid to the solution. After the fluorine has thus been bound, perhaps in the little dissociated anion, BFI-, a complete precipitation of the tin as sulfide can be made in a glass vesseL7 Alternately, it was pointed out that the tin can be deposited electrolytically after the addition of oxalic acid.* The current efficiency was extremely
N
associated with tin in alloys-namely, cadmiumq2 copper, lead, bismuth,2 arsenic, and antimony-may be separated completely from quadrivalent tin by precipitation with hydrogen sulfide in solutions which contain a moderate concentration of hydrogen fluoride (about 1 per cent by weight). In his comprehensive scheme of qualitative analysis, Noyes3 made mention of the possible use of dilute hydrofluoric acid solutions of certain metals in quantitative analysis. McCay has proved that the separations from tin are quantitative in the cases of antimony,4 lead,5 ~ o p p e rand , ~ arsenica6 His experiments prove that the separations are successful only when antimony and arsenic are present quantitatively in the trivalent, and tin in the quadrivalent state. Iron and zinc, if present, will be found in the filtrate which contains the tin. Preliminary results indicate that under the Received M a r c h 23, 1923. Thus far qualitative experiments only have been made in the instances of cadmium a n d bismuth. See Footnote 4 8 Tech. Quauterly, 16, 93 (1903); 17, 214 (1904) 4 J . A m . Chem. Soc , 31, 373 (1909). S I b z d . , 34, 1241 (1910). I b i d . , 4S, 1187 (1923). 1
2
’
F u r m a n , J . A m . Chem. S O C ,40, 895 (1918). T h e details which are described in Classen-Hall, “Quantitative Analysis by Electrolysis,” 6th ed., 1913, p 135, John Wiley & Sons, Inc , were followed. 7
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