V O L U M E 19, NO. 2, F E B R U A R Y 1 9 4 7 100
where from which
=
K
M of n-heptane =
3.03
An unknown sample is then run with which 21.0 units of liquid cause a pressure increase corresponding to 125.0 mm. of bubble travel a t 26 O C . The density of the liquid is 0.720 and its molecular weight is calculated from Equation 1:
M =
21.0 X 0.720 X 3.03 X 299 = 125.0
Table I shows typical results on a variety of compounds of It appears that good accuracy is maintained until C.P. quality. . the vapor pressure-of the substance falls below approximately 0.2 through the disk mm. of mercury. At this and in spite Of heating is not complete* This becomes very sets a practical upper limit for molecular weights of hydrocarbons
137 a t about 170, corresponding to a CIIH~sparaffi. Inasmuch, however, as the boiling points of such compounds are in the vicin-' ity of 200" C., most of the gasoline boiling range hydrocarbons within the "Ope Of the apparatus' I n this work no attempt Was made to thermostat the nor to shield any parts except the micromanometer from air currents, and room temperature near the apparatus was used in all calculations. LITERATURE CITED
(1) Farkas and Melville, "Experimental Methods in Gas Reactions", New York, Macmillan Co., 1939. (2) Glasstone, "Textbook of Physical Chemistry", p. 311, New York, D. Van Nostrand Go., 1940. (3) Reilly and Rae, "Physico-Chemical Methods", vole 11, New York, D. Van Nostrand Co., 1939. ( 4 ) Taylor and Young, IND. ENG.CHEM.,ANAL.ED.,17,811 (1945). (6) Young and Taylor, ANAL.CHEU.,19, 133 (1947).
Microdetermination of Tetraethyllead in Gasoline B. E. GORDON AND R. A. BURDETT Wood River Research Laboratories, Shell Oil Co., Inc., Wood River, I l l .
A micromethod for the determination of tetraethyllead in gasolines is based upon decomposition with iodine, followed by the volumetric determination of precipitated lead chromate. The elapsed time is considerably shorter than that required by conventional methods, and the sample required is only 1 to 5 ml. The accuracy and reproducibility of method conform to A.S.T.M. specifications.
T
HE production of fuel for civilian and military consumption
has emphasized the need for a rapid, accurate method of determining the lead content of gasolines. Commercial blending operations can be greatly facilitated if data as to lead content are provided with a minimum of elapsed time. I n studies of engine manifold distribution and fuel decomposition, often only small quantities of gasoline are available for analysis. A method of analysis of such small quantities, having the accuracy of accepted macroanalytical procedures, would not only provide valuable data in these studies but expedite other investigations previously limited by the lack of an appropriate analytical method. HISTORICAL
Various methods have been proposed for the determination of tetraethyllead in gasolines. Some of these have been based on an acid extraction of the lead (2, 3, 7,8,11,12), others on the decomposition of the tetraethyllead by a halogenating agent (4, 6, 9, 13). Lykken el al. (IO) recently conducted a thorough investigation of several existing methods and made suitable recommendations regarding the attainment of accuracy and precision. Aborn and Brown (1) and Clark (6) developed rapid instrumental methods for determining lead in gasolines.
911 the methods re\+ewed required from 50- to 200-ml. samples and most of them were time-consuming. The instrumental methods lacked the accuracy and precision desirable in this analysis, and some of the chemical methods had to be modified when applied to gasolines rich in aromatics or olefins. In none of the methods suggested does the application of microanalytical technique with its accompanying advantages seem to have been investigated. The ease of manipulation, simplicity of equipment, and accompanying rapidity of a suitable micromethod indicate the advantages if applied to determinations of tetraethyllead. I n addition, the small samples necessary for analysis eliminate the difficulty attendant on the handling of large quantities of difficultly oxidizable organic residues. PRINCIPLE OF METHOD
The method is based on the decomposition of the tetraethyllead with iodine, evaporation of the volatile constituents, destruction of the organic residue with mixed sulfuric, nitric, and perchloric acids, and subsequent volumetric microdetermination of precipitated lead chromate. A simple antispatter device eliminates all loss due t o energetic reaction and ebullition, and the use of a platinum Monroe micro filter stick overcomes many disadvantages inherent in filtration. Once the gasoline is added to the flask, the entire analysis is conducted without transfer; thus a serious source of error is eliminated. APPARATUS
.,.a %I".
