INDUSTRIAL AND ENGINEERING CHEMISTRY
648
VOL. 30, NO. 6
son of their value as antiseptics, the corresponding normalities are given in Table 111. Mole for mole, calcium chloride is more effective than any of the salts of monovalent metals tested. When normalities are considered, however, calcium chloride gives results comparable to those obtained with the other metallic chlorides. While there is no significant difference shown between the bacteriostatic action of sodium, potassium, and calcium chlorides in terms of normalities, the corresponding values for sodium nitrate are noticeably lower, indicating that the nitrate ion is slightly more effective than the chloride ion.
Sodium chloride is effective in about one-half the concentration a t a p H of 5 as it is a t a p H of 6 . The other salts tested give similar results. With respect to the bacteriostatic and bactericidal properties of benzoic acid, related compounds, salt splutions, and possibly many of the commercial antiseptics, the authors postulate a “hydrogen-ion effect.” Subsequent reports will correlate the p H of the menstruum with the relative effectiveness of some of the commercial antiseptics.
Summary
This project was sponsored by the Mallinckrodt Chemical Company, under the general supervision of H. V. Wallingford and R. N. Shreve.
The maximum dilutions a t which benzoic acid solutions function effectively as bactericidal or bacteriostatic reagents were determined a t various p H values against Bacterium coli and Staphylococcus aureus. The results indicate that the effectiveness of these solutions increases, up to a maximum, with an increase in the hydrogen-ion concentration. Solutions of calcium, potassium, and sodium chloride, and of sodium nitrate and sulfate are not effective as bacteriostatic reagents except a t rather concentrated solutions a t a p H of 5 or 6. The bacteriostatic properties of the chlorides are approximately the same when expressed in terms of normality, but the nitrate and the sulfate are slightly more effective.
Acknowledgment
Literature Cited “Hydrogen Ions, Their Determination and Importance in Pure and Industrial Chemistry,” New York. D. Van Nostrand Co., 1932. Goodhue, L. D., Iowa State Coll. J. Sci., 10,No. 1, 7-16 (1935). Kuroda, T., Biochem. Z . , 169, 281 (1926). Reddish, G . F., J. Lab. Clin.Med., 14, 649 (1929). Waterman and Kuiper, Rec. trau. chim., 43, 323 (1924).
(1) Britton, H. T. S., (2) (3)
(4) (5)
RECEIVED January 29. 1938. Presented before the Division of Medicinal Chemistry at the 95th Meeting of the American Chemiaal Society, Dallan, Texas, April 18 to 22, 1938.
Heats of Dilution of “Mixed Acids” F.H.RHODES AND C . c. NELSON Cornell University, Ithaca, N. Y.
I
The total heats of dilution of various mixtures of sulfuric acid, nitric acid, and water were determined. The data permit the computation of the heat changes involved in the mixing of strong sulfuric acid and strong nitric acid, and in the changes in composition and concentration of acid that accompany nitrations made with mixed acid.
N THE nitration of a hydrocarbon by means of a mixture
of strong nitric and strong sulfuric acids, the net heat change is the algebraic sum of the heat of reaction of the hydrocarbon with nitric acid to form the nitro derivative and water, the heat evolved by the dilution of the unused acid to the final concentration of the spent acid, and the heat change involved in the withdrawal of the reacted nitric acid from the mixed acid. I n most instances information is available from which the heat of reaction may be computed; data from which the other heat quantities may be calculated are fragmentary. McDavid (3) determined the heats of mixing involved in the preparation of ternary mixtures of sulfuric acid, nitric acid, and water from the pure components. Only comparatively few of the mixtures prepared by him were within the range of composition of commercially important “mixed acids.” His method of procedure involved the assumption that the specific heats of mixed acids are constant over wide ranges of temperature; this assumption may not be justified. Because of the fragmentary and possibly inexact nature of the available data, the present investigation was undertaken. I n this work the total integral heats of solution of, mixed acids were measured which contain various known percent-
ages of nitric acid, sulfuric acid, and water. These measurements provide the data necessary for the computation of t h e heats of mixing or the heats of dilution between known initiaL and final concentrations of water.
Apparatus and Procedure The method used involved essentially the dilution, in a. calorimeter, of known weights of mixed acids of known composition and the measurement of the resulting heat evolution: The calorimeter was made from a 2-liter Dewar tube provided with an insulated cover through which were inserted a Beckmann thermometer, an electrically driven stirrer, and a glass rod provided with a terminal loop to hold the sample bulb. The calorimeter was charged with 1500 grams of water, and a thin-walled sealed glass bulb containing a weighed portion of the analyzed mixed acid was placed on the loop and immersed in the water. After stirring for a period long enough (15 minutes) t o ensure thermal equilibrium and a uniform and very small rate of change of temperature, the “radiation rate” was determined by taking temperature readings at 30-second intervals. By means of the glass rod the glass bulb was broken below the surface of the water. Stirring was continued until the rate of temperature change was again very slight and uniform. The change in temperature caused by the dilution of the mixed acid was computed
JUNE, 1938
INDUSTRIAL AND ENGINEERING rCHEMISTRY
-
TABLEI. INTEGRAL HEATS OF DILUTION ob R u n No.
MS MN MS MW
la 0.2500 0.0433 0.2933 0.0046 0.980 1.545 2.822 4.362 14.87 0.016 284 333 0 23 15.10
+N
2 6T I(M
*
A¶ Aza
6c&/MM
-
R u n No.
lo 0.2093 0.1732 0.3825 0.0053 0.977 1.546 2.865 4.43 11.58 0.014 217 398 0.09 11.67
MS MN M S -k N MW CP H
AT
Q
!XM Aa
Ala A&/ M Qc/M Q
0.2413 0.0418 0.2831 0.1232 0.981 1.548 2.310 3.573 12.62 0.435 294 345 0.21 12.83
0.2202 0.0882 0.2584 0.2439 0.982 1.55 1.671 2.59 10.02 0.943 323 379 0.17 10.19
0.2123 0.0367 0.2490 0.3887 0.982 1.551 1.271 1.971 7.92 1.56 336 394 0.14 8.06
5a 0.205 0.0350 0.2375 0.809 0.983 1.56 0.755 1.178 4.96 3.41 354 415 0.12 5.08
54.7 Moles HzS04:45.8 Moles HNOs 2c 3c 4c 0.1850 0.2418 0.2202 0.1532 0.1996 0.1820 0.3382 0.4414 0.4022 0.1414 0.3612 0.592 0.979 0.974 0.976 1.458 1.552 1.555 2.102 2.338 1.562 3.255 3.628 2.429 9.62 8.21 6.04 0.418 0.818 1.47 247 190 208 450 346 380 0.04 0.13 0.10 9.66 8.34 6.14
The symbols have t h e following meanings: S = sulfuric acid W = water N = nitric acid M = gram moles C p = specific heat of final diluted solution estimated from d a t a for specific heats of dilute HNOa and dilute H z S 0 4 (8) H = total heat capacity = (weight of final solution X Cp) f water equivalent of cablorimeter A T = temperature rise C. Q = heat liberated = ' H A T , Kcal.
by extrapolating the initial and final radiation lines in the usual
way. All determinations were made at 18 C. The water equivalent of the caIorimeter (49 grams) was determined in the same way; in place of mixed acid, samples of strong sulfuric acid of known concentrations and known integral heats of dilution (1, 2) were used. O
The measurements of the rise in temperature should be accurate within 0.01 O C.; this represents an error of not more
I
18' A
HEATS OF DILUTION OF
MIXED
I
ACID
1 I I
*'IDso
1-
8 5 . 3 Moles Hz80r:14.7 Moles "0s2a 38 4a
lb
,
0.2470 o,3555 0.1085
)
'
69.5 Moles HsSOa:30.5 Moles " Os 2b 3b 4b
ll:~l~~
. 0.987
0.0052
-.
47 5 6s,0.10 11.70
'
50 0.2033 0.1683 0.3716 1.079 0.978 1.565 0.918 1.436 3.87 2.91 226 415 30..9058
E::Xig 0.2578
0.1625 0.984 1.55 1.683 2,609 10.12 0.631 323 466 0.03 10.15
13.05 234 338 '.l8 13.23
649
t:gS%O
0.3195 0.4079 0.980 1.553 1.545 2.400 7.51 1.282 262 377 0.14 7.65
5b
6b
0.2060 0.0907 0.2967 0.634 0.981 1.556 1.082 1.684 5.68 2.14 283 406 0.10 5.78
0.2008 0.0881 0.2889 1.006 0.982 1.564 0.741 1.159 4.01 3.485 292 419 0.09 4.10
-39.2 Id 0.11~~7
;: o ,:3 0&?54 0.9z; 1.54&
4":3
10.1g3 0.0 198 506 11 L3
7::
Moles HaSOr:60.8 Moles HNOa 2d 3d 4d 0.1123 0.1745 0.1859 0.1750 0.2718 0.2892 0.2873 0.4463 0.4751 0.0777 0.450 0.917 0.982 0.973 0.973 1.544 1.549 1.560 1.674 1.773 1.315 2.581 2.747 2.051 6.15 4.32 8.98 0.27 1.008 1.93 290 187 177 740 480 453 -0.08 0.01 0.03 8.90 6.16 4.35
.
5d 0.1572 0.2448 0.4020 1.219 0.976 1 565 0.783 1.225 3.05 3.03 210 537 -0.02 3.03
- heat tiberated per gram mole of acid Kcal /gram mole (mol, s HzO)/(moles total acid) in original sample = (mol, 9 HzO)/(moles total acid) i n diluted solutlon =
= (mol HzO)/(moles H2S04) i n diluted = coTr( on (see &MI,, K,cal. = corrtped heat of dilution per mole of
solution total acid t o such a finab concy&,r~t~on.that the molar ratio of HzO t o HzS0.r is 500:1, Kcal./grrtm mole
than 1 per cent in the determinations made with the most dilute solutions and the smallest temperature rises. The specific heats of the final diluted solutions were estimated from the published values for the specific heats of very dilute nitric acid and very dilute sulfuric acid (2) ; they are probably accurate within 1 per cent. The final results are probably exact within about *O.l Kcal. The acids used were of c. P. quality. They were separately analyzed by the titration of weighed portions with a standard solution of sodium hydroxide. I n the preparation of mixtures of very low water content, i t was necessary to use nitric acid that had been concentrated by two successive distillations, under a pressure of 50 111111. of mercury, with an equal volume of concentrated sulfuric acid. During the distillation a slow stream of air was admitted through a very fine capillary, below the surface of the boiling mixture; this not only prevented bumping but removed nitrogen oxides from the distilled acid. The mixtures were prepared from weighed portions of t h e analyzed individual components. About 25 cc. of each mixture, in a thin-walled sealed glass bulb, were used in each determination.
Data on Heats of Dilution
MOLS
H 2 0 PER
MOL
FIGURE1
ACID
I n most cases the molar ratio of water to acid in the final dilute solution was between 200 and 300; with much higher dilutions the temperature rise would have been so small that the accuracy of the measurements would have been impaired. There was some unavoidable variation in the molar ratios of water to total acid and of water to sulfuric acid in the final diluted solutions. Beyond the final concentrations used in these experiments the further heat of dilution of nitric acid is negligible; sulfuric acid does, however, show a definite, although small, further heat of dilution. T o make the data more strictly comparable among themselves, B correction was applied to adjust the values to a standard
I-
-
HEATS OF DILUTION OF MIYIED ACID
f
320
final concentration of 500 moles of water to 1 mole of sulfuric acid. This correction is computed as:
-
(&"I
QaX)
where Q8'
=
Q." =
x
molar ratio of H2S04 to HNOS in the mixture total integral heat of dilution of &SO4 t o concentration of 500 moles HzO : 1 mole H2S04 total integral heat of dilution of H2SO4 to concentration of final solution in calorimeter
This correction assumes that in these low concentrations the further heat of dilution of sulfuric acid is not altered by the presence of the nitric acid. Since the correction itself is small, even in those experiments made with a high ratio of sulfuric to nitric acid, any error due to the invalidity of this assumption is negligible. Because of the difficulty in reading closely the graphs given by McDavid (S), a n accurate general comparison of these results with his is not possible. Where his individual experiments were made with mixed acids in the range of the compositions studied here, recomputation of the specific data indicates good general agreement between the two sets of results, although there are a few discrepancies. Tables I and I1 show the data obtained.
F -PURE HN(
Application To make use of these data in computing the heat evolved during an actual nitration, it is convenient to regard the process as taking place stepwise. If we assume a composition of mixed acid and consider the formation of 1 mole of nitrobenzene, we may write: (initial acid, Ai) + (intermediate acid, A2)
+ "0s
' 0
4
8
12
I6
20 24
28
32
36
40
44
CsHe
FIGUBE 2
- &SA, - Q S H N O ~
+ HNOs +CaH6NOt + HzO &a
Run
Integral Heat of Diln. with 500 H~SOI:HNO~-.-Hg0 in Mixt.-Moles HzOMoles/ mole yo bu Kcal.1 B.t. u , / Molar Bg weight acid wt. 8. mole lb. soln. 100-0 100-0 0.0 0.0 18.26 335 1.5 8 . 4 2 14.53 244 1.0 15.5 11.57 179 1.5 21.6 9.47 136 2.0 26.9 8.28 111 3.0 35.5 6.56 78 85.3-14.7 90-10 0,016 0.3 15.10 292 0.435 7 . 7 8 12.83 229 0.943 15.47 1 0 . 1 9 167 1.56 23.22 8.06 120 3.41 39.8 5.08 59 69.5-30.5 78-22 0.015 0.3 13.23 272 0.277 5 . 4 0 11.70 228 0.631 1 1 . 5 1 0 . 1 5 183 1.282 2 0 . 9 7.65 125 2.14 30.6 5.78 83 3.485 4 1 . 8 4.10 49 $4.7-45.3 65.3-34.7 0,014 0.3 11.67 255 0.418 8.40 9.66 194 0.818 15.2 8.34 155 1.47 24.4 6 14 102 2.91 38.9 3.95 53 39.2-60.8 50-50 0.013 0.3 10.13 236 0.27 5.97 8.90 196 1.008 19.15 6 . 1 6 117 1.93 31.2 4.36 70 3.03 41.6 3.03 41 0-100 0-100 0.0 0.0 7.43 212 1.0 22.2 4.16 92 2.0 36.4 2.65 48 3.0 46.2 1.72 26.5
Q Q
-Ratio
F r o m I. C. T. ( 8 )
la 2a *3a 4a 5a lb 2b 3b 4b 5b 6b IC 20 3c 4c 5, Id 2d 3d 4d 5d From I. C. T.
SUMMARY OF D A T A Q3
(8)
(2)
Qnitration
(intermediate acid, A z ) TABLE 11.
(1)
= QSA~
&I
-
+ H2O(spent + acid, Aa)
+-Qz + Qs-
= &SA,
= Qi = &SA,
(3)
&SA,
QSA~
&S"Oa
f
Qnitration
The total heat liberated is therefore equal to the heat of solution of the initial mixed acid, minus the heat of solution of the final spent acid, minus the heat of solution of 1 mole of pure nitric acid, plus the heat of the nitration reaction. The use of the graphs (Figures 1 and 2) in a computation may be illustrated as follows: Suppose we wish to find the total integral heat of solution of a mixture of 1.7 moles of sulfuric acid, 1.3 moles of nitric acid, and 1mole of water. Since the molar ratio of sulfuric acid to water is 0.333 to 1 and the molar ratio of sulfuric to nitric acid is 56.7 to 43.3, we read on the graph (Figure 1) representing this ratio of sulfuric to nitric acid the ordinate corresponding to an abscissa of 0.333. This ordinate (10.3) multiplied by the total number of moles of mixed acid ( 3 ) gives the total integral heat of solution (30.6 Kcal.).
Literature Cited (1) Bichowsky a n d Rossini, " T h e r m o c h e m i s t r y of Chemical Substances," New York, Reinhold Publishing Co., 1936. (2) I n t e r n a t i o n a l Critical T a b l e s , Vol. V, N e w York, McGraw-Hill Book Co., 1929. (3) M c D a v i d , J. mi.,S.SOC.Chem. I n d . , 41,246T(1922).
RECEIVED December 29, 1937.
650
