give conversion rights into common shares at prices significantly below those of a year ago. Foreign financing of subsidiaries of U.S. companies (C&EN, Aug. 1, 1966, page 26) floated about $450 million in securities last year, compared with $350 million in 1965. Mr. Kirwan-Taylor added that although this rising U.S. demand for internationally underwritten issues has drawn criticism in Europe, it has actually helped develop the market in both size and technique. The growing demand for available funds has reduced the size of individual loans. Mr. Haas gave the average loan value as $16.5 million in 1966—down from $21 million the previous year. Size of an individual loan depends heavily on the reputation of the borrower. The director advised his audience, "The more your company will be known [through such publicity means as secondary stock issues], the cheaper and easier it will be for you to call on the market." French banker Haas also foresees increased participation by European Economic Community nations in the international capital market. Existing exchange controls in EEC will probably disappear rapidly unless there is a major recession, he says.
Isotope data track Pb sources Measurement of isotopic ratios in ancient objects made of lead can tell archaeologists a good deal about the sources of the lead, according to Dr. Robert H. Brill of the Corning Museum of Glass (Corning, N.Y.) and Dr. J. M. Wampler (now at Georgia Institute of Technology, Atlanta). While at Brookhaven National Laboratory (Upton, N.Y.), Dr. Wampler used a thermal emission mass spectrometer to measure the isotopic compositions of 60 samples, collected by Dr. Brill. The samples included ores from ancient mining areas and lead from archaeological objects [Am. J. Archaeol, 7 1 , 63 (1967)]. The isotopic compositions of the ancient objects vary over a wide range. But many objects fall into one of three definite groups. And the isotopic compositions of several objects made of lead from specific mining areas match the isotopic compositions of lead ores obtained from the same areas. Lead is unusual in that the relative proportions of its isotopes vary among ores occurring in different geographical areas, Dr. Brill explains. These variations reflect differences in the geological ages of the ore deposits and stem from the fact that 2 0 6 Pb, 2 0 7 Pb, and 2 0 8 Pb form as end products of
Ancient Pb ingot Ore mined in Roman Britain
The isotopic ratio technique alone can't pin down the source of lead in an ancient object, the two chemists point out. But it does permit conclusive negative judgments. For example, Dr. Brill concludes from the isotopic composition that the lead pottery cover excavated at Ur definitely did not come from Laurion or any other mine in the Laurion group. A disadvantage of the isotope technique is that the ratios are changed by the re-use and mixing of leads from different sources. If leads from different sources are remelted together, the resulting isotope ratios will be intermediate between those of the individual leads. But the technique has an advantage over chemical analysis; the isotope ratios are unaffected by the chemical history of the metal.
Pb ups exhaust hydrocarbons
Pb pottery cover from Ur Data rule out Greek source the radioactive decay series of uranium and thorium. With the mass spectrometer, Dr. Wampler determined ratios of the four lead isotopes with masses 204, 206, 207, and 208. The data were plotted as the ratios 208pb207pD VSm 2oepD207pb and 2O6pD204pb VSt 206pb207pb.
From the plots of the isotopic ratios, Dr. Brill and Dr. Wampler found that many samples arranged themselves into three groups. Samples in a particular group had similar isotopic compositions. The first group includes lead ores mined in Spain and Wales and also includes leads from Sardinia. The second group includes ores mined in Roman Britain. The third group, called the Laurion group (for Laurion, Greece), includes central and eastern Mediterranean samples. Among the ancient samples studied by the two chemists is a lead ingot (from the British Museum collection) made in England during the Roman Period. Its isotopic composition agrees with that of ores mined in Roman Britain (from deposits whose isotopic composition has been checked). Another sample (from the University Museum, University of Pennsylvania) is a lead pottery cover excavated at Ur, Iraq. Its isotopic composition places it in the group comprising ores from Spain, Wales, and Sardinia. But since its date is so early (about 3000 B.C.), it couldn't have been made from lead mined in any of these regions, Dr. Brill says.
A Ford Motor Co. study shows that leaded gasoline may cause a significant increase in hydrocarbon content of auto exhaust emissions. Vehicles operated on leaded gas for 24,000 miles showed a 156-p.p.m. increase in hydrocarbon exhaust emissions over similar cars using nonleaded gas, James C. Gagliardi of Ford's engineering research laboratory told the meeting of the Society of Automotive Engineers in Detroit. (See page 18 for more on the SAE meetings.) The Ford study was run under controlled driving conditions with a sixcar test fleet at Ford's Michigan proving grounds. Results showed that, after 12,000 miles, the exhausts of cars using leaded gas contained 42% more hydrocarbons than when the test started, as measured by infrared analysis. By 24,000 miles, the increase reached 5 1 % . For cars using unleaded fuel, hydrocarbon content of the exhaust rose only 12% after 12,000 miles. It decreased with continued running, and was about 5% above the starting point after 24,000 miles. To confirm the results, cars which used leaded gas were switched to nonleaded fuel at 24,000 miles and showed a 13% reduction in hydrocarbon emissions after 6000 additional miles. Carbon monoxide and oxides of nitrogen concentrations were not affected by the leaded gas. The mechanism of the increase in hydrocarbon emissions is not definitely known, Mr. Gagliardi says. But noting that the removal of combustion chamber deposits from test-car engines also lowered the hydrocarbon emission, he surmises that the different types of deposits which occur in engines with leaded and nonleaded fuels may account for the increase. Leaded gas builds up deposits that JAN.
23, 1967 C&EN
17
are porous and have an irregular surface; this could cause an increase in the surface-area-to-volume ratio in the cylinder. Such a condition could cause more rapid quenching of the flame front and result in more unburned hydrocarbons. The study has already stirred some controversy. Spokesmen for Du Pont, Esso, and Ethyl Corp. were quick to point to their own test results which led them to conclude that leaded gas has no effect on auto exhaust emissions. Dr. Alden J. Pahnke of Du Pontes petroleum laboratory notes that the Ford results were based on IR analysis of the exhaust gases. He points out that nondispersive IR (NDIR) analysis has a poor response to aromatics, which comprise 36% of unleaded gas. Leaded gasolines are about 22% aromatic. Dr. Pahnke says that, in a Du Pont study, hydrocarbon concentrations of exhaust measured by flame ionization analysis showed no significant increase for leaded gas, although the same samples measured by NDIR did. Further study confirmed that more than half of the increase detected by NDIR could be traced to variations in fuel composition, he adds. When this variation was compensated for, the increase in hydrocarbon emissions from leaded fuels was not significant by either flame ionization or NDIR. Like the Ford study, the Du Pont study showed no effect on carbon monoxide or oxides of nitrogen. Dr. Norman Alpert of Esso Research & Engineering told SAE that Esso tests have uncovered no evidence that leaded gasoline affects the hydrocarbon exhaust emissions. For example, in 1964 the company ran a test involving 12 autos of the same type used in the Ford test. After 45,000 miles of taxi fleet operation in a small urban community, no significant effect on hydrocarbon emission was attributed to leaded fuel. Dr. Alpert concludes that a closely controlled driving cycle involving a rapid accumulation of mileage (as in the Ford test) is likely to amplify any difference in hydrocarbon emissions. Dr. Alpert calls for further studies with larger test fleets that include cars equipped with emission control devices. One such broad-based vehicle test of leaded gasoline is already under way and more are being planned. The American Petroleum Institute last September contracted for a threeyear, $480,000 study by the Bureau of Mines in Bartlesville, Okla. This test will study the effect of leaded gas on evaporative losses, total exhaust concentrations, and exhaust emission reactivity. Another API study, not yet contracted, will extend the leaded18 C&EN JAN. 23, 1967
nonleaded gas comparison to cars equipped with emission control devices. Also, the Automobile Manufacturers' Association is interested in participating in a "carefully considered" joint research program. Commenting on the significance of the Ford test, Mr. Gagliardi says that Ford is not taking a position on possible prohibition of leaded fuels.
ELCD stops auto gas vapors Esso Research and Engineering scientists have demonstrated the feasibility of a technique for essentially eliminating an important source of automotive air pollution—evaporation of gasoline from a vehicle's fuel tank and carburetor. The technique uses an evaporation-loss control device ( E L C D ) , which adsorbs hydrocarbon vapors on charcoal, then feeds the vapors to the engine for burning. The device, developed by P. J. Clarke, Dr. J. E. Gerrard, Dr. C. W. Skarstrom, Dr. J. Vardi, and D. T. Wade, is for use on new cars. It does not alter engine operation or increase exhaust emissions of hydrocarbons or carbon monoxide, the Esso Research group said at the Automotive Engineering Congress and Exposition of the Society of Automotive Engineers, in Detroit. Gasoline evaporation is one of three primary sources of automotive hydrocarbon emission. The other two are exhaust and crankcase fumes. An automobile with no control devices emits about 530 pounds of hydrocarbons a year, according to Esso Research. Crankcase ventilation devices used on late-model cars reduce hydrocarbon emissions to about 400 pounds
a year per car. Adding exhaust-control devices to meet the requirements of California's Motor Vehicle Pollution Control Board further reduces emission to about 180 pounds. Eliminating gasoline evaporation cuts this remainder to about 90 pounds a year per car. E L C D operates on a controlled adsorption-desorption cycle. A canister of charcoal traps vapors before they escape into the atmosphere. It holds the vapors until they can be desorbed and fed into the engine. A purge control valve allows the hydrocarbons to desorb into the engine at an appropriate time and rate. This enables the charcoal to adsorb more hydrocarbons. The third component of the system is a pressure-balance valve which maintains carburetor performance. With the engine off, the internal seat of the pressure-balance valve leads all hydrocarbon vapors from the carburetor bowl to the canister. All tank vapors also pass to the canister. As soon as the engine is started, the intake manifold vacuum changes the position of the pressure-balance valve, blocking the internal port and restoring carburetor metering forces to their design values. The purge control valve depends on exhaust back pressure. At idle, during deceleration, or at low cruising speed, exhaust back pressure is too low to unseat the valve and there is no purging (stripping the canister of hydrocarbons). However, under acceleration or at cruise speeds above 30 miles per hour, the valve unseats and the canister is purged with clean air from the air cleaner. According to Esso Research, the system surpasses the evaporative targets established by California pollution control officials.
FROM AIR CLEANER
PRESSURE BALANCE VALVE
CANISTER
FUEL TANK
-
TO EXHAUST MANIFOLD
Evaporation-loss control device Operates on controlled adsorption-desorption cycle
