Ethylene plant in West Germany More demand, greater capacity
Matthews, executive vice president in charge of Gulfs U.S. chemical operations. Overcapacity in the Free World will be less severe than the totals for capacity and demand might indicate, say both Pace and Arthur D. Little. This is because older units that are less economical to operate will likely be shut down. Also, some announced plants will be delayed or deferred (as has already happened during the past year). Effects of overcapacity also should be less severe than the estimates indicate. Actual ethylene production seldom exceeds 90% of "name plate" capacity when averaged over a year, says Pace. In 1966, when U.S. capacity was strained, production was 10.2 billion pounds, or 89.6% of a careful estimate of the then available capacity of 11.4 billion pounds. Salt dome storage and the pipeline system on the Gulf Coast made possible this high use of capacity.
NBS studies may produce filling that bonds to teeth An adhesive dental filling material that would bond tightly to tooth structure would be one promising way to overcome a common enough problem—the further decay and often eventual death of a tooth following restoration. Such a material could well 16 C&EN JULY l f 1968
emerge from studies on tooth structure at the National Bureau of Standards. NBS research workers find, for example, that not only the mineral phase but the collagenous material at prepared dentinal surfaces of a tooth may offer potential sites for bonding. Dr. Eugene F. Huget and Dr. Gerhard M. Brauer of the NBS dental research section point out that lack of information about the chemical and physical characteristics of the surfaces of the components of tooth structure has retarded progress toward development of a truly adhesive restorative. They filled in some of that lack, however, at the 42nd National Colloid Symposium, held in Chicago by the ACS Division of Colloid and Surface Chemistry. In their current study, Dr. Huget and Dr. Brauer made calorimetric measurements of the heats of immersion of human dentin, enamel, and an organic whole tooth tissue of known specific surface. They then quantitatively determined the nature and degree of surface modification produced by various ions and functional groups in aqueous environment. Investigations by others have shown that human dentin contains 18 to 19% proteinaceous material and that the most abundant is collagen. In an aqueous environment, the collagen adsorbs water. Amine, guanidyl, and carboxyl groups as well as the hydroxyl groups of serine and hydroxyproline are important in this adsorption. As a result, Dr. Huget and Dr. Brauer point out, immersion of dentin powders results in binding of water by the accessible polar groups of the collagenous matrix as well as adsorption of water by the inorganic phase. Under the proper environmental conditions, certain ions and functional groups interact preferentially with the collagenous matrix. For example, Dr. Huget and Dr. Brauer studied the immersion of powdered dentin in aqueous solutions containing certain anions—iodide, nitrate, nitrite, sulfate, and thiocyanate—at pH 5. The depressed heats of immersion observed, they say, suggest the direct endothermic interaction of the anions with quaternary ammonium groups. An alternative mechanism may involve preferential binding of the anions to positively charged sites on the dentinal collagen at water's expense. There was a slight decrease in heats of immersion when the aqueous solution was a dilute base. But Dr. Huget and Dr. Brauer do not feel that ionic bonding to charged groups of the dentinal collagen took place. Rather, they say, it's more likely that removal of protons from positively charged amine groups limited the ability of these groups to bind water.
Fixed standards for individual air pollutants attacked "Setting fixed standards for individual pollutants does not rest on sound evidence nor promote effective air pollution control." This was the opinion expressed by Dr. Eric J. Cassell, M.D., associate professor of community medicine at Mt. Sinai School of Medicine, New York City, at the Air Pollution Control Association meeting last week in St. Paul, Minn. Dr. Cassell cites sulfur dioxide as an example. Sulfur dioxide is present in urban atmospheres at very low concentrations, except under most bizarre and rare circumstances, he says. The peaks are usually not above 1 p.p.m., which is about the bottom of the range used in laboratory studies. When concentrations of sulfur compounds increase, concentrations of numerous other substances, which may or may not have an effect on man, will increase at the same time. Therefore, it is difficult for the scientist to know whether an effect is caused by sulfur compounds, other materials, or a combination. Also, there are atmospheric substances about which nothing is known, Dr. Cassell points out. The conductivity-type instrument generally used to measure sulfur dioxide in the air only reflects sulfur dioxide when that gas exists alone—an ideal that is rarely met. However, legislation which proposes a numerical standard for sulfur dioxide does not deal with what is represented; it deals with the gas sulfur dioxide, he says. The effect of sulfur dioxide on man is further complicated by effects of temperature, humidity, cigarette smoking, infection, allergy, stress, emotional factors, and other disease determinants. Reorganizing these complexities in finding relationships between the concentration of a specific pollutant and a specific reproducible effect in man will not weaken air pollution control efforts, Dr. Cassell points out. "It forces us to find solutions that take them into account. If simplistic research approaches have failed, so probably will simplistic legislative approaches. In fact, individual standards may not achieve clean air but may well delay effective air pollution control. "The control should be based on the concept of controlling pollution emissions to the greatest degree feasible employing maximum technological capability. If the degree that is presently feasible were met in all industries, the air would be much cleaner without necessarily threatening the economic structure of an industry."
