INDUSTRIAL A N D ENGINEERING CHEMISTRY
January 15, 1931
does not exceed an accuracy of 0.005" C. The melting point of oxonium perchlorateis thus found to be 49.905' 0.005"c. NO evidence of the transition of Reaction 1 above was found. Perchloric acid monohydrate has not, therefore, been shown to exist and the oxonium structure of perchloric acid of this theoretical composition thus indicated.
+
61
Literature Cited (I) (2) (3) (4) (5) (6) (7)
Beckman, z. physzk. Chem ,ai, 239 (1896). Goehler and Smith, IND.END.CHEM.,Anal. Ed., 3, 55 (1931). International vO1. I, P. 57* Kanolt, Bur. Standards, Sci. Paper 520. Smith and Koch, IND. CHEM,, Anal Ed,, s, 52 (1931), Volmer, Ann., 440, 200 (1924). Wyk, van, Z . anorg. Chem., 48, 1 (1906).
Oxonium Perchlorate as Reference Standard for Construction of Specific Gravity-Percentage Composition Table for Strong- Perchloric Acid Solutions' G . Frederick Smith and 0.E. Goehler DEPARTMENT OF CHEMISTRY, UNIVERSITY OF ILLINOIS, URBANA, ILL.
Oxonium perchlorate (OH,CI04, m. p. 49.905" C.) is HE chemical analysis Previous Work used for t h e preparation of known strengths of conof strong solutions of centrated perchloric acid solutions. perchloric acid in the Published work closely reA determination of t h e density of strong solutions region of 65 to 75 per cent acid lated to the present investigaof perchloric acid is described and t h e construction of tion is found in the investistrength is obtainable only by a density-acid composition chart over t h e range 65 to the application of an indirect gations by van Wyk ( 8 ) ,van 75 per cent perchloric acid carried out. The determethod. A reference acidiEmster ( I ) , and Hantzsch (3). mination of t h e constants used in t h e calculation of metric standard is first used The data of these investigainterpolated a n d extrapolated values is given. to standardize the solution of tors ( r e c a l c u l a t e d in some The determination of reference points in t h e denB base which is then in turn cases to gain uniformity for sity-acid composition chart established t h e density used for the analysis of the the purpose of easy compariperchloric acid solution in of t h e dihydrate of perchloric acid at 25"/4" C. t o be son) as applied to the deter1.71282. Constant boiling perchloric acid 72.4 per question. This indirect analmination of the density of percent at 760 m m . and 203" C. has t h e approximate ysis is made necessary by the chloric acid of strength 73.60 density 1.6964. f a c t that a s a t i s f a c t o r y per cent (the dihydrate commethod has not been develposition) is given in Table I. oped for the reduction of perchlorates to chlorides which could The values obtained as hereinafter described are included then be determined using silver. The preparation of an accu- to conserve space. rate density-percentage composition table within the range under question is desirable because concentrating dilute Table I-Density of 73.60 Per C e n t Perchloric Acid a n d Related Constants solutions of perchloric acid either a t atmospheric pressure COEFFICIENT OF or under reduced pressure gives rise to acid within this range DENSITY EXPANSION INVESTIGATOR 25'/4O C. Alpha Range d A/dC of percentage composition. Perchloric acid, when distilled c. a t 760 mm., forms a constant boiling mixture with water van Emster 1.70942 0.00121 15-30 ., ., .. ., .. 0.01351 0 01390 1.7130 0.00121 20-50 which consists of 72.4 per cent acid. The formation of the van Wyk . . ... 1.42064 0.01366 Hantzsch 1.71299 approximate dihydrate of perchloric acid (OHaC104.H20) Present work 1.71282 0.00122 20-30 1.42052 0.01343 which has an acid composition of 73.60 per cent results from di - dz Alpha --- (change in density per degree change in acid the vacuum distillation of perchloric acid of constant boiling t r - 11 concentration). strength (2,6,6, 7). The object of the present paper is the construction of a Outline of Procedure density-percentage composition table, the accuracy of which exceeds that of existing data, using a method which can be Samples of oxonium perchlorate (84.794 per cent HClO4) demonstrated to be superior to such data, and employing are prepared by the method of Smith and Goehler and their methods of chemical analysis only. The method of attack exact composition and identity determined by the determinais wholly dependent upon the accuracy with which the melting tion of their exact melting point (49.905' C.). Weighed point of the highest melting hydrate of perchloric acid can be portions of these samples of oxonium perchlorate are then determined (2) (OHaC104, m. p. 49.905' * 0.005" C.). diluted with weighed portions of pure water and a density This product, by consulting the data of van Wyk (8) can determination made of the solutions thus prepared. The easily be seen to serve better than any other known form of identity of the density thus found for solutions of the same perchloric acid as a reference point in the analysis of strong acidity based upon the dilution of the individual preparations perchloric acid following the cryoscopic method, and inde- of oxonium perchlorate serves as an additional evaluation pendent of chemical analysis. of the uniformity in composition of the high melting hydrates as determined by their melting point. Further dilution 1 Received August 23, 1930. A portion of a thesis presented by 0. E. of the samples thus formed serves for the determination of Goehler in partial fulfilment of the requirements for the degree of doctor other points on the density-acid composition curve. From of philosophy in the Graduate School of the University of Illinois.
T
,
O
A N A L Y T I C A L EDITION
62
the data thus accumulated the change in density per interval of change in acid composition is readily calculated and the agreement with a linear function thus examined. The analyses are, therefore, dependent only upon physical observations.
C
Preparation of Solutions of Known Acid Composition
Vol. 3, No. 1
The densimeter tube is shown in Figure 2 and had two ground glass stoppers, A and D. Ground joint A provided for the introduction of the sinker and sample. Ground joint D supported the upper and lower suspensions and was protected against introduction of moist air by use of the side tube, C, through which a slow stream of dry air was passed during the period of time in which stopper D was disengaged. The densimeter tube was maintained at a constant temperature with an accuracy of * 0.01" C . using the large Dewar tube thermostat shown in Figure 3. The water of the thermostat bath was provided with mechanical stirrer, heating coil, and cooling coil, and its temperature was recorded by a Callender platinum resistance thermometer with compensating leads, using a speci9ly designed Wheatstone bridge. The movement of the gplvanometer by means of a system of lights and m i r r w w s t an image on a scale above the balance. By=ttiag the Wheatstone bridge a t the properly calculated setting for a given temperature, the bath temperature during measurement was closely controlled by use of a switchboard controlling the heating and cooling coils and stirrer of the thermostat. The platinum resistance thermometer was calibrated at the ice point, the freezing point of mercury, and the boiling point of water. The volume of the sinkers employed was found to be as follows:
Oxonium perchlorate prepared as previously described (2),having the melting points 49.905" * 0.005" C., was t r a n s ferred to the lower portion of the reaction tube shown in Figure 1 in the 73io 9 0 Id following manner: foil The m e l t i n g p o i n t t u b e c o n t a i n i n g the oxonium perchlorate was placed in the upper portion of the reaction tube after the tip was broken to provide for the transfer of the contents. The stopper with a thin gold foil covering is inserted No. 1 No.2 and the whole apparatus Mass, grams 66.3081 21.5544 dried by evacuating a Volume: number of times and re200 c. 28.5512 28.5528 250 c. 9.6170 filling with dry air. The 28.5545 30' C. whole r e a c t i o n tube Figure 1-Reaction Figure )--DenTube simeter Tube was then immersed in Distilled water was used as the calibration liquid and the a water bath a t 55" C. best values for its expansion with change in temperature. up to the height of the stopper and the contents of the melting The calculation of the densities determined was made using point tube melted and allowed to collect in the lower part of the following formulation. the reaction tube. It was then fused at the constriction, and from the original weight of the tube and the two parts after the transfer of the oxonium perchlorate, the weight of the sample was obtained. = density of sample at temperature t D -t The weighed sample tube of oxonium perchlorate was S 4 = relative weight of sinker plus suspension file-marked at the neck, reweighed, and the tube opened. A W = relative weight of sinker in liquid plus suspension weighed quantity of water was then added and the tube 2 and Y = respective vacuum corrections for S and W = volume of sinker at temperature t resealed. The composition of the resulting acid was then Vt calculated and the density determined. The latter operations The results of series of determinations of points of reference were repeated and a new acid concentration and density to be used in the construction of a density-percentage compodetermined. sition chart for concentrated perchloric acid solutions are found in Table 11. Determination of Density of Concentrated Perchloric Acid
The determination of the density of concentrated perchloric acid was carried out following the displacement method described in Bureau of Standards Bulletin 9 (4). The balance emplQyed and the arrangement of the suspensions in the present work provided for an accuracy of * 0.4 mg. Weights were calibrated and the vacuum corrections applied as well as corrections for atmospheric conditions, including psychrometer relative humidity, temperature, and barometric corrections. The displacement sinker was made of Pyrex glass rod molded into shape, annealed 48 hours at 300" C. to minimize thermal hysteresis, and allowed to age for 10 days. The sinker was suspended by a platinum wire having a diameter of 0.0035 inch dull goldplated over the immersed portion to insure wetting by the perchloric acid and avoiding the phenomena associated with "sticking" which is thus best eliminated.
Table 11-Determinations of Points of Reference Used in Construction of Density-Percentage Composition Chart VACUUM: VACUUM VACUUM WT. WT. RESULTWT. ANHYD. HClOa ING DENSITY HClO4 Grams
36.3531 30.7492 40,0530 40.3712 41.6093 35.4381
HClOa
91" 84.794" 84.794" 73.082 72.257 70.107 73.094
HClO4 Grams
29.9774 26.0735 29.2715 29.1710 29.1710 25.9031
+ HtO
Grams 41.0190 35.6712 40.5097 41.6093 46.2831 36.5718
HClO4
%
73.082 73.094 72.257 70.107 63.027 70.828 a Oxonium perchlorate (OHsC104), m. p. 49:905' b Change in density per degree change In acidity.
25'/4'
C.
dA/dCb
1.70583 .. . . . 1.70608 1.69478 o:oi84i 1.66582 0.01344 1.57104 0 01358 1.67552 0.01345 * 0 006' C.
From an examination of this table it will be observed that the value for d A/dC (the change in density per unit change in per cent) within the experimental error shows the relationship to be linear over the 70-73 per cent acid concentration, an average value of 0.01343 being obtained. The agreement between the present work and the value obtained by van Emster (1) is better than that obtained
January 15, 1931
I N D UXTRIAL ANDlENGINEh'RING CHEMIETRY by comparison with van Wyk (6) or Hantzsch (3). The value d A/dC, 0.01343, together with the data of Table 11, gives for the density of 73.603 per cent HClOI (the OH3C10gHz0 hydrate) the value 1.71282 with a probable accuracy of 5 units in the fifth place of decimals. Here the agreement is closer between the present work and that of van Wyk and H a n t z s c h , (Compare with Table I.) The determination of the coefficient of expansion resulted in a substantial agreement between the present work and previous observers (8, 1, 3). Between 63 and 70 per cent acid concentratjon the value for dA/dC increases slightly. Construction of Density-Acid Composition Table for 65 to 75 Per Cent Perchloric Acid
c
. b
Io
,-N
3
The data of Table I1 serves for the construction of a table of values relating density and Figure 3-Dewar T u b e acid. comaosition. The values _ obtained are included in Table 111.' Values given other than those for the exact multiple of 0.25 per cent in acid composition are the result of actual observation. The re-
63
mainder are calculated. The values of the density experimental reference points are intended to be accurate to 5 units in the fifth decimal place and the acid composition to within * 0.01 per cent. Values for the calculation are as follows: d A / d C = 0.01343 between the limits 70 to 75 per cent acid composition, and d A / d C = 0.01351 for the remainder. The calculated values for the density of Table I11 are thought to be accurate to the fourth decimal place. Table 111-Density
and Percentage Composition of 65-75 Per C e n t
Perchloric Acid DENSITY DENSITY DENSITY DENSITY HClOa 25'/4' C. HClO4 25'/4' C. HClOa 25'/4O C. HC!O425'/4' C ,
%
63.0270' 1.57104 65.00 1.59665 65.25 1.60002 65.50 1.60340 65.75 1.60678 66.00 1.61016 66.25 1.61353 66.50 1.61691 66.75 1.62029 67.00 1.62367 67.25 1.62704 67.50 1.63042 67.75 1.63380 68.00 1.63718
%
..
. ..
%
. . . 71.25 68.25 1.64055 71.50 68.50 1,64393 71.75 68.75 1.64731 72.00 69.00 1.65060 72.25 69 25 1.65406 72.257" 69.50 1.66744 72.50 69.75 1.66082 72.75 70.00 1.66420 73.00 70.107" 1.66582 73.082" 70.25 1.66756 73.094" 70.50 1.67092 73.25 70.78 1.67427 73.50 70.828" 1.67552 73.75 ... 71.00 1.67763 74.00 a Values experimentally determined. d A / d C 60-65% = 0.01351 65-75% 0.01343 t
.....
% 1.68099 1.68434 1.68774 1.69106 1,69442 1.69478 1.69778 1.70113 1.70449 1.70583 1.70608 1.70785 1.71120 1.71456 1.71790
74'.25 74.50 74.75 75.00
... ... ... . .. ...
... ... . .. .. .. ..
i:+iii4 1.77458 1.72791 1.73125
..... .....
.....
.. . ....*
,,
.....
.... . ..... ..... .l...
Literature Cited (1) Emster, van, 2. anorg. Chem., 62, 220 (1907). (2) Goehler and Smith, IND.ENG.CHEM.,Anal. Ed., S, 55 (1931). (3) Hantzsch, 2. p h y s i k . Chhm., A 144, 147 (1929). (4) Osborne, McKelvey, and Bearce, Bur. Standards, Bull. 9, 328 (1913). (5) Smith and Goehler, IND. ENG.CHEM, Anal. Ed., s, 48 (1931). (6) Smith and Goehler, I b i d . , 3, 58 (1931). (7) Smith and Koch, Ibid,, s, 52 (1931), (8) w y k , van, z. them., 48, 1 (1906).
An Improved Absorption Tube for Combustion Analysis' W. D. Turner DEPARTMENT OF CHEMICAL ENGINEERING, COLUMBIA UNIVERSITY, NEW YORK,N. Y.
Light weight. Plain internal design-surface accessible to wiping. Ground joint external-not contaminated in charging. Simple construction-low cost.
INCE the advent of solid absorbents, such as Ascarite, for combustion analysis, many designs of absorption tubes have been proposed involving more and more advantages over their predecessors; yet none of them possessed at the same time all the refinements of manipulation combined with simplicity of design. To meet this need an apparatus, diagramed in the accompanying illustration, was devised. The innovation consists in using an external instead of an internal stopper, allowing the cut-off of both openings without the use of return bends or other bypasses. This renders possible a simplification of design with the following advantages : Minimal outside surface-easy to wipe to constant weight. Minimal parts-one body, one stopper, one ground joint. Minimal surface contour-low breakage. Simple, positive operation-one turn of one stopper shutting inlet and outlet short off. (This was the particular point sought, so that for combustions in oxygen there would be no diffusion of air into the absorber during the operation of disconnecting.) Minimal waste space-larger capacity completely utilized. Stable standing.
* Received
October 13, 1930.
Absorption B o t t l e f o r Solid Absorbents Round glass body, 1 , 2 ; external stoooer. 3. 4: lateral tubes. 5 . gr&d joint 6 . t o tube attadhed to inner sid; df body neck, 7, 8; depressed channel communicating with the top interior, 10.
Absorbers of this type have been in satisfactory use in the laboratories of the Bakelite Corp o r a t i o n and a t Columbia University, a n d have been readily made t o o r d e r by the glass-blowing dep a r t m e n t s of Eimer and Amend and Columbia University.
