Aug.,
1920
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
taken t o ensure complete extraction before reporting solubilities. SOLUBILITY IN WOODALCOHOL
.... ., .. .. ...... .. .. .. .. .. .. .. .. ..,. .... ..
Commercial shellac.. Stick-lac.. ,,.
..... . .
91.66 per cent 8 1 . 4 per cent
T h e stick-lac was t h a t referred t o , containing 8.5 per cent of woody matter. I wish t o acknowledge indebtedness t o my colleague, Mr. J. D. Stuart, who did much of t h e work incidental t o t h e above investigation.
78 r
tures as low as -72' C. were obtained. Where possible, a standardized mercury thermometer was used, but a t extremely low temperatures a toluene-filled thermometer which had previously been compared with t h e mercury thermometer, was used. Extreme
THE FREEZING POINTS OF MIXTURES OF SULFURIC AND NITRIC ACIDS1 By Walter C. Holmes EASTERN LABORATORY, E. I. DU
P O N T D3
NEMOURS & CO.,CHESTER, PA.
Mixtures of sulfuric and nitric acids, commonly designated as mixed acids, are used in enormous amounts in t h e chemical industry in nitration processes, as carried out in the explosive and dye industries. Owing t o a case where a mixed acid had become frozen during storage, under conditions where freezing seemed improbable, determinations of t h e freezing points of a large number of mixed acids were carried out in this laboratory. The original object of t h e work was simply t o obtain empirical d a t a regarding t h e temperatures of freezing for different mixtures. The results, however, were of exceptional interest, as indicating t h e formation of a definite chemical compound between sulfuric and nitric acids. While thethorough explanationof thephenomena observed was beyond t h e scope of t h e work, i t is believed t h a t t h e presentation of these results will be of value as an addition t o t h e knowledge of mixed acids. The only chemical compound of sulfuric and nitric acids which could be found in t h e literature is t h a t mentioned by Weber12 who gives i t t h e composition 4 S 0 ~ . N ~ O s . 3 H 2 0though , this composition does not seem proved. T h e most thorough study of t h e properties of mixed acids appears t o have been carried out by Saposchnikow,s who investigated particularly t h e vapor pressures, specific gravities, and conductivities of such mixtures in all proportions.
% HMO,
%H,O
supercooling was met with, one case occurring where t h e acid did not freeze at a temperature over 6 0 " C. below t h e t r u e freezing point, as subsequently deter.mined. As a rule, however, solidification could be induced b y inoculation of t h e sample with a small crystal of frozen acid, care being taken t h a t this.crysta1 should be from a n acid of similar composition. Precautions were also taken t h a t , in t h e final determinations on an acid, t h e surrounding bath should not be more t h a n a few degrees lower t h a n t h e freezing point of t h e acid.
EXPE R I M E " IAI.
Three sets of mixed acids were made u p of 100,gj, and 103 per cent total acidities, respectively, SO t h a t in each set of acids t h e only variables were t h e sulfuric acid and t h e nitric acid contents. The nitric content of t h e mixtures was varied from zero t o approximately 50 per cent in t h e I O O and g j per cent mixtures, and u p t o about 30 per cent in t h e 103 per cent mixtures. I n all cases t h e compositions of the mixtures were determined by careful analysis. T h e freezing was carried out in test tubes of about one inch diameter, t h e thermometer being used as stirrer. The test tubes were immersed in an insulated bath. The freezing mixture consisted of ether and carbon dioxide snow, b y means of which tempera1 Read at the 59th Meeting of the American Chemical Society, St. Louis, Mo., April 12 to 16, 1920. 2 Ann. Phys. Chem. (Pogg.), 142 (1871), 602. 8 2 physik. Chem., 49, 697; 51, 609; 63, 225 (1904-1905).
The exact procedure was as follows: A sample was frozen by cooling below t h e t r u e freezing point and b y subsequent inoculation or vigorous stirring, as t h e case demanded. T h e temperature of freezing was noted, this temperature being taken a t t h e highest point reached, as in all cases a rise in temperature took place a t t h e time of solidification. The b a t h was then, regulated t o not more t h a n 4' or 5 O below t h e temperat u r e recorded, and a second sample was frozen. This. procedure was repeated until t h e highest point a t which an acid would freeze had been found and checke& several times.
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
78 2
The freezing point values given in the table were obtained by this method: FREEZING POINTS
MIXED ACIDS Total Acidity (Per cent)? FREEZING POINT HNOSOa HzO O c. OF
Series A-lOO%
-COMPOSITION Actual Actual HzS0.l ”01 ... 1 100 96.24 2 3.05 O:i4 0:47 5.38 0.30 0.59 93.73 3 4 91.95 7.83 0.39 -0.17 10.20 0.49 -0.02 89.33 5 10.80 0.53 0.00 88.67 6 12.61 0.54 -0.08 86.93 7 13.76 0.63 0.68 8 84.93 84.85 13.90 0.64 0.61 9 16.93 0.73 0.84 81.50 10 17.06 0.36 -0.19 82.77 11 17.20 0.76 0.36 81.68 12 0.67 19.70 0.85 78.78 13 0.31 24.59 1.04 74.06 14 0.24 29.24 1.65 68.87 15 39.40 1.60 0.17 58,83 16 48.95 17 48.84 1.93 0.28 Series B-Q5% Total Acidity 94.96 1 2.35 0:65 5:68 92.52 2 5.16” 5.69 0.04 89.11 3 4.89 7.36 0.03 87.72 4 5.56 9.75 0.19 84.50 5 11.72 0.02 5.45 82.81 6 5.76 15.20 0.40 78.64 7 4.34 20.40 0.04 75.22 8 4.18 25.70 0.07 70.05 9 4.87 30.15 0.15 64.82 10 5.67 39.02 1.13 54.18 11 44.04 49.09 1.33 5.54 12 Series C-103% Total Acidity 1 103.0 0164 -3.37 100.25 2.48 2 6.31 0.12 -3.30 96.87 3 7.89 0.65 -3.47 94.93 4 8.15 0.42 -3.01 94.44 5 0.23 -3.08 92.07 10.78 6 0.58 -2.68 90.36 11.74 7 0.58 -2.98 90.38 12.02 8 14.25 0.77 -3.66 88.64 9 15.52 0.33 -3.15 87.30 10 20.08 0.39 -3.18 82.71 11 0.59 -3.09 77.48 25.02 12 0.79 -2.27 72.85 28.63 13 -9.3’ is interpolated 1 The freezing point given Knietsch Ber. 84 (1901),4100: At tde time this work out, no iumini sulfuric acid free from small amounts available. ACID
No.
...
...
..
.
I, i n n
I-.-
-2.2 -18.2 -15.1 -0.7 +2.3 fZ.0
+l.O 4-1.4 -1.4 -1.5 -1.6 -5.1 -11.5 -19.0 approx, -40,0 -50.0 iapproxj -26.0 -41.0 -19.5 -13.5 -11.0 -12.0 -16.0 -20.0 -22.0 -20.5 -21.8 41.3
Vol.
12,
No. 8
sulfuric acid and water, t h e dihydrate HzS04.HzO. Reasoning from analogy, i t seems probable t h a t t h e maximum in t h e sulfuric acid-nitric acid curve also represents a definite compound, between sulfuric a n d nitric acids, since t h e addition of either component will depress the freezing point of t h e mixture. Further evidence in favor of t h e formation of a definite compound is t h e fact t h a t i t was repeatedly found t h a t inoculation of t h e acid mixtures with a crystal of sulfuric acid would not induce solidification. T h e use of a crystal of frozen mixed acid was necessary in almost all cases. T h e maximum point in t h e sulfuric acid-nitric acid curve comes a t a point where t h e nitric acid content is 10.80 per cent. It is significant t h a t Saposchnikow found t h e density of such mixtures t o attain a maximum when the nitric content was between I O a n d 12.5 per cent. T h e acid mixture having a nitric content of 10.8 per cent represents almost exactly t h e combination 5 HzS04. H N Os.
I
I
-9.3’ -2.8 -1.5 -11.0 -12.3 -6.0 -1-1.7
+3.0
+8.5 +10.5 +8.0 +2.0 -11.0 from the table of was being carried of nitric acid was
D I S C U S S I O N OF RESULTS
T h e results tabulated above show t h a t t h e addition of nitric acid first depresses t h e freezing point of sulfuric acid. On addition of further amounts of nitric acid, a rapid rise in t h e freezing point takes place, until a maximum is reached. A general similarity is seen between the freezing-point curves for t h e three sets of acids. The curves for t h e mixtures containing 95 per cent and 103 per cent total acidities (Fig. 11), however, are somewhat complicated by t h e presence of a third component, water in t h e one case and free sulfur trioxide in the other. Two maxima occur in each curve. For this reason, no attempt has been made t o explain t h e form of these curves. A marked similarity, moreover, is seen t o exist between the freezing-point curve of sulfuric acid a n d nitric acid (100 per cent total acidity) and t h a t of sulfuric acid and water (Fig. I).’ I n t h e latter case, t h e curve falls t o a minimum of - 3 4 O C. when 8.4 per cent water is present; then rises t o a maximum of +8.0° C. with a water content of 15.5 per cent. I n the case oE sulfuric acid and nitric acid, t h e minimum comes a t -18.2‘ C., with a nitric content of 5.5 per cent, a n d t h e maximum a t 2.3 O , when approximately I 1.0per cent of nitric acid is present. T h e maximum in t h e sulfuric acid-water curve represents a definitely known compound between
+
1 The fr-ezing-point curve for sulfuric acid and water is based.on data given by Knietsch, Ber., 84 (1901),4100.
I n the freezing-point curve for sulfuric acid and water, while t h e maximum comes a t t h e composition HzS04.HzO, t h e preceding minimum comes a t t h e composition HzS04-1/zH20. It may be a coincidence, b u t i t is a t least a n interesting one t h a t in t h e sulfuric-nitric acid curve the maximum comes a t t h e composition 5H2SO4.HNO3 and t h e preceding minimum a t t h e approximate composition 5H2S04-1/2HN0a. Saposchnikow did not reach any conclusion as t o whether a compound was formed between sulfuric a n d nitric acids. It was his belief, however, t h a t in mixed acids with a sulfuric content higher t h a n 80 per cent, t h e nitric acid was dehydrated, with formation of nitric anhydride. This view of Saposchnikow, regarding t h e condition in which nitric acid is present in mixed acids, is questioned b y Marshall.’ 1
“Explosives,” 2nd Ed., 1917, p. 123.
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T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
783
then pulverized t o 60 mesh and t h e residual moisture I-Freezing-point determinations were made on determined b y heating a one-gram sample for one three sets of mixtures of sulfuric a n d nitric acids, having hour at 10.5' C.l Experiments made by t h e Bureau2 total acidities of 100,95, and 103 per cent, respectively, have shown t h a t total moisture in coke can be determined with adequate accuracy ( * 0 . 5 per cent) for and nitric contents varying from zero t o 5 0 per cent. a-The freezing-point curve for t h e IOO per cent most purposes by simply heating t o constant weight acidity mixtures was found t o reach a minimum when a large sample of lump coke, in any convenient oven, t h e nitric acid content was 5.4 per cent. The maxi- or on a stove, hot plate, or steam coil, a t a temperature mum was a t t a i n e d with a nitric acid content of 10.8 of 105'to zooo C. per cent. T h e curve showed a marked resemblance The standard methods of analyzing coke as given t o t h a t of sulfuric acid and water. by t h e American Society for Testing Materials8 state 3-It seemed probable t h a t t h e composition, a t t h e t h a t t h e total moisture shall be determined by drying above maximum, represented a definite chemical t h e entire sample received at t h e laboratory without compound between sulfuric and nitric acids, t h e acids any preliminary crushing t o constant weight at a at t h a t point being present in t h e proportion 5H2SO4- temperature of not less t h a n 104' or more than zooo "01. C., and t h a t t h e loss in weight is t o be calculated as 4-The freezing-point curves for t h e 9 j and 103 per percentage of moisture which shall constitute t h e total cent mixtures were complicated by t h e presence of a moisture in t h e coke as received in t h e laboratory. third constituent. No attempt, therefore, was made The sample for analysis crushed t o a fineness of 60 t o explain them. mesh is prepared from t h e dried coke without any regard t o changes in moisture content. Moisture is then determined on t h e 60-mesh material by heating HYGROSCOPICITY OF BY-PRODUCT COKE' a one-gram sample of t h e coke for one hour in a suitBy W. A. Selvig and B. B. Kaplan able oven at a temperature of 104' t o 110' C. T h e FUELSCHEMICAI, LABORATORY, PITTSBURGH EXPERIMENT STATION, PA. BUREAUOF MINES, PITTSBURGH, moisture obtained on t h e 60-mesh material is used Received April 9, 1920 simply t o calculate t h e determinations made on this The experiments described i n this paper were under- material t o a dry basis. The total moisture as detertaken. in order t o obtain d a t a as t o t h e amount of mined on t h e lump size sample is taken as t h e total moisture absorbed by dry pulverized coke on exposure moisture content of t h e coke, and t h e air-dry figures, t o air of varying humidity in connection with methods2 are then calculated t o t h e "as received'' condition. used in many commercial laboratories for t h e analysis OUTLINE O F E X P E R I N E N T S of coke. Four samples of coke were selected for t h e tests, I n these methods t h e sample for total moisture one sample of beehive coke and three samples of bydetermination is taken from t h e regular sample for product coke. These samples had been previously analysis by reserving one or more rejected quarters air-dried and crushed t o pass through a 60-mesh sieve. after t h e sample has been crushed t o half-inch size. The analysis and origin of these samples are given in Moisture is determined in I O lbs. or more b y drying t o Table I. approximately constant weight at a temperature of TABLEI-AIR-DRIED 60-MESH COKE SAMPLES USED IN TESTS 105' C. T h e laboratory sample for analysis is prePER CENT pared by crushing and reducing t h e regular sample ORIGINOF Mois- Volatile Fixed No. SAMPLE ture Matter Carbon Ash Sulfur until about one pound of 40-mesh material remains. 31177 Connellsville 72-hour beehive A sufficient amount of this 40-mesh material is transfoundry c o k e . . . . . . . . . . . . 0 . 1 5 1.56 89.09 9.20 0 . 7 8 31075 By-product furnace coke from ferred t o a bottle and dried for one hour a t 105' C. Franklin County, Ill., coal 0 . 9 8 2 . 5 3 83.79 12.70 0 . 8 8 33754 By-product domestic size coke No moisture determination is made in t h e laboratory (source of coal unknown). 0 . 5 0 1.98 85.79 11.73 0 . 8 2 31677 By-product domestic size coke on t h e dried material, i t being assumed t h a t t h e coke frornPittsburghbedcoa1.. 0.56 2 . 8 0 79.46 17.18 0 . 8 9 will not absorb appreciable amounts of moisture from t h e air. It is evident t h a t , if t h e pulverized sample One-gram samples of t h e 60-mesh coke were weighed of coke did absorb appreciable amounts of moisture i n duplicate into porcelain capsules, dried i n an oven between t h e time of drying and t h e weighing of t h e for one hour at 105' C., cooled over sulfuric acid i n various portions for analysis, t h e analysis would be in desiccators, and weighed, t h e loss i n weight being error corresponding t o t h e amount of moisture absorbed. recorded as moisture. I n order t o prevent any changes T h e volatile matter determination, especially, would in moisture during t h e weighing of t h e samples, all be too high. weighings throughout t h e test were made by placing STANDARD MOISTURE DETERMINATION METHODS t h e porcelain capsules containing t h e samples in glass When a high degree of accuracy is desired, t h e weighing dishes provided with tightly fitting ground moisture in coke is determined in two stages. The caps. coke is crushed t o one-half or one-quarter inch size The uncovered crucibles and contents were placed and air-dried t o approximately constant weight at a in one-quart Mason jars containing mixtures of sultemperature of 30' t o 35' C. T h e air-dry sample is SUMMARY
Published by permission of the Director of the Bureau of Mines. * United States Steel Corporation, "Methods for the Commercial Sampling and Analysis of Coal, Coke, and By-products," 1916, p. 18. 1
1 F. M. Stanton and A. C. Fieldner. Bureau of Mines, TechnicaE Pager 8 (1913), 7. 2 A C. Fieldner and W. A. Selvig, Ibid., 148 (1617), 14. 8 Am. SOC.Test. Mat. Standards. 1919, 711.
