V O L U M E 20, NO. 1 2 , D E C E M B E R 1 9 4 8 s50.85obtiiined by tlie pendent drop mcytliod by Bartell and Davis ( 3 ) . Thc values shown for carbon tetrachloride are somewhat highcr than the 43.44 by the capillary method reported by AInck arid I3artell (1). The only serious discrepancy betwmi values according to tlie capillary method and the corrected ring method was that found s i t h the solution containing 50.7% of heptane. Thii ir. not surprising in view of the fact that the density of this solution is greater than that of water by only 3%. I t was shown in the previous paper (10) that the corrected ring method loses accuracy in the range of densities less than that of water by the order of 2'3. Thus the corrected ring method for determining interfacial tension appears to be equally applicable, regardless of whether the ring is being pulled upnard from water to the organic liquid lighter than water or pushed downward from water to organic liquid heavier than water. I n either case the method loses accuracy as the densities of the two phases approach each
1245 other. However, even in this range the corrected value is far more accurate than the uncorrected figure. LITERATURE CITED (1) Ani. SOC. Testing hlaterials, Committee D2, Proc. Am. SOC. Testing Materials, 43, 275-50 (1943). (2) Am. SOC.Testing Materials, Method D357-46. (3) Bartell, 17. E., and DiZYiJ, J. K., J . Phys. Chem., 45, 1321-36 (1941). (4) Bartell, F. E., and hliller, F. L., J . Am. Chem. Soc., 50, 1961-7 (1925). (5) Gerell, G. IT., il.S.T.Jf. Bull. 146, 92-5 (May 1947). (6) Harkins. W. D., and Jordan H. I?., J. Am. Chem. SOC.,52, 175172 (1930). (7) Mack, G. L., and Bartell, F. E., Zbid., 54, 936-42 (1932). (8) von Fuchs, G. H., Wilson, N. B., and Edlund, K. R., IND.E m . C H E M . , A S A L . ED., 13, 306-12 (1941). (9) Walsh, E. F., A.S.T.M. Bull. 146, 95-8 (May 1947). (10) Zuidema, H. H., and Waters G. W., Ibid., 13, 312-13 ( 1 9 4 1 ) .
RECEIVED May
5 , 1948.
Determination of Acetone ROBERT E. BYRNE, JR. K e d d e Chemical Laboratory, East Lansing, Mich.
q L D C I I Y D E S arid ketones react with hydroxylamine hydrochloride, forming oximes and releasing hydrochloric acid. Titratiori of the free acid has been the basis for many methods of analysis of carbonyl compounds. The acid causes a measurable drop in pH, which is the basis of the method described in this paper. J17herl acetone reacts \YitIi dilute solutions of hydr&laI,lille hydrochloride there is a definite relation between pH change and quantity of acetone present. I t has been pointed out by Marasco ( 1 ) that this reaction is not complete; however, this factor is accountcd for, as the method is calibrated for each set of samples and then becomes quantitative. Other factors affecting accuracy lire the dilution of hydroxylamine hydrochloride used, the accuracy of pII readings, and possibly normal laboratory atmosphere, althougli no such effect has been noted. The method describcd is accurate for small amounts of acetone up to 23 micrograms per ml. Thc extent of pH change ii iiot
::\
apprcciably altcred by variation in temperature between 20' and 30" C.
Procedure. To 5 ml. of 5c0hydroxylamine hydrochloride solutiorl in a 25-ni1. volumetric flask enough acetolle is added to the concentration after dilution not greater than 25 mlcrograms per ml. The resulting mixture is then diluted to 25.0 ml. hfter thowugh mixing, the pH of the solution is measured with a pH meter. (A Leeds I%Xorthrup pII meter was used in this investigation,) ~l~~ concentration of acetone may be determined from a previously prepared standard curve of pH against concentratioxl of' acetone (Figure 1). Table I.
Effect of Ethyl Alcohol Ethyl Alcohol, $101. 70 0 4 8 12 16 20 24
PH 2.44 2.44 2.43 2.43 1.41 2.42 2.41 2.40 2.42
28 32
3.21
pH 2.6
The standard curves s!iown in Figure 2 are plots of the data obtained from the determination of known amounts of acetone nhich were alloncd to react a i t h (A) 0.5 nil. of the hydroxylamine hydrochloride solution, and ( B ) 0.1 ml. of the standard solution, according to the piocedurc described above. The hydroxylamine hydrochloride solution used may be stored foi 2 to 3 days but gradually becomes more acid, and it is reconimended that a fresh solution be used each day. INTERFEREVCES
- I \
2.2
ACETONE, MICROGRAMWML. Figure 1
In mixtures of acetone and kyater, ethyl alcohol has been added up to 30% by volume with no apparent affect on the pH change (Table I). A4cetonein benzene or petroleum ether may also be determined by this method, by first extracting the acetone from the benzene or ether with water. The water mixture from the extraction is allowed to react with hydroxylamine hydrochloride in the manner described. The results of a determination of this type are shown in Table 11. Consistent pH readings could not be obtained by this method from acetone present in 1,4-dioxane. Acetone in acid-free n-amyl alcohol could not be determined. Any substance that exhibits an acidic or basic reaction in water, and the presence of
1246
'I
ANALYTICAL CHEMISTRY
-_
Table 11. Determination of Acetone Acetone Present,
4.
{
Acetone Found,
3.8
Substances Present
PH
Y
0 2.4 4.7 6.3
3.25 2.77 2.56 2.47
0 2.4 4.7 6.3
Ben Ien e
0
3.25 2.06 1.96 3.25 2.26 2.02
0 19.7 27.6 0 11.1 23.7
Dioxane
Y
4 7 7.9 0 4.7 9.5
%-Amyl alcohol
SUM.MARY
A rapid, accurate method for the determination of acetone present in concentrations of about 25 niicrograms per nil. or less depends upon the calibration of a standard curve, a plot of known quantities of acetone zs. pH, for each set of samples. Acctone may then be directly determined by pH measurement. The range of sensitivity of the curves may be extended by varying the concentration of hydroxylamine hydrochloride used. Dcterminations arc not perceptibly affected by variations of room temperature from the norm (20' to 30' C.). Kormal laboratory atmospheres.apparently do not influence the accuracy of the results. ACKNOWLEDGMENT
The author wishes to express appreciation to Fredcrick R. Dukc: for his guidance and assistance.
Figure 2 other carbonyl compounds, will interfere with this determination. .ketone may not be determined by this method in solvents from which it cannot be completely extractcd with water.
LITERATURE CITED (1) Marasco, M., Znd. Eng. Chem., 18, 701 (1926). RECEIVED October 31, 1947.
Modification of Hershberg Melting Point Apparatus for Internal Heating and Silicone Fluid FREDERIC C. XIERRI.AM' Haroard C'nicersity, Cambridge, Mass.
URINC; the 12 years that have elapsed since Hershberg ( 7 ) D described his precision melting po'nt apparatus design, silicone fluids for high temperature heat transfer have been discovered. These fluids, which are now commercially available, are superior to sulfuric acid in that they are noncorrosive and are cwellent melting point bath fluids a t temperatures far above the boiling point of either sulfuric acid or mineral oil (6, 8). Like mineral oil they are nonconductors of electricity and permit direct heating with a coiled resistance wire immersed directly in the fluid without excessive discoloration or oxidation of the fluid. The apparatus of earlier design (7), using mineral oil, denionstrated the advantages of internal heating, but had to be put aside because of the shortcomings of mineral oil in this application. White and Hartwell (6, 8) have recently used equipment of similar design for tests on fluids. At temperatures up to 150" C., Present address, Department of Chemistry, Boston University, Boston, Mass. I
Graft' (6)employed infrared light for internal heating, but its use is necessarily restricted. The apparatus described below employs a nev heater design, with suitable provision for the greater expansion of the silicone fluids on heating. With its rapid response it is possible to select quickly and to maintain a series of increasing bath temperaturcs. This is necessary in order to determine the instantaneous decomposition points of unstable compounds (1). Dow-Corning silicone fluid Type 550-1 12 centistoke viscosity grade has been used successfully in this laboratory for temperatures up to 360" C., and the 500-50 centistoke grade is satisfactory for temperatures up to 300 O C. APPARATUS
The construction of the apparatus is illustrated in Figure 1. The tube and sleeves were constructed of larger tubing than is ordinarily used for a Hershberg apparatus, so as to have more space for the heater and melting point capillaries. An expansion
