The continuously regenerating trap (CRT) is a diesel exhaust emission control that removes nearly all diesel particulate matter on a mass basis, but under some circumstances oxidation of sulfur leads to the formation of nanoparticles. The objective of the four year study was to determine CRT performance under controlled, real-world, on-road conditions, and to develop quantitative relationships between fuel and lubrication oil sulfur concentration and particle number exhaust emissions. It was shown that nanoparticle emissions are minimized by the use of ultralow sulfur fuels and specially formulated low sulfur lubrication oil. Nanoparticle emissions increased with higher exhaust temperatures. Fuel and lubrication oil sulfur increased the particle concentration by, on average, 36 x 10(6) and 0.14 x 10(6) part/cm3 for each 1 ppm increase in sulfur. On the other hand there was a decrease in nanoparticle emissions by the CRT as the system aged.

The basic ferric acetate precipitation procedure used for removing phosphate from solutions in which silica is to be determined has been critically investigated. I t has been found that unless strict control of the pH is observed the method may give inaccurate results, owing to (a) incomplete removal of phosphate or (b) removal of silica with phosphate.Previous work has been confirmed that both phosphate and silica couple with molybdate in weak acid, but that only the silicomolybdate complex is reduced in strong acid. On this principle a new procedure for determining silica in biological material has been developed, in which phosphate is left in solution.Iron, in amounts greater than those occurring in tissue, has been found not to interfere.In urines with high phosphate concentrations two methods have been evolved to overcome interference by precipitation of ammonium phosphomolybdate. In one, phosphate is partly or completely removed by precipitation with calcium hydroxide; in the other, ammonia and urea are removed with nitrous acid and sodium molybdate is used to couple with silica.The new colorimetric procedure gives good agreement with gravimetric analyses, and good recoveries of added silica have been obtained with tissue, blood and urine. The procedure likewise gives results in good agreement with gravimetric methods,. when applied to small samples of mineral dusts.SILICON may be determined chemically by gravimetric, titrimetric and colorimetric procedures. All methods depend on the decomposition of siliceous material to liberate silicic acid. In the gravimetric method silicic acid is subsequently dehydrated to the oxide of silicon, and the silica, SiO,, is isolated and weighed. The silica so isolated often contains small amounts of metallic salts, and for this reason it is usual to treat the impure silica with hydrofluoric acid, which completely volatilises the silicon as silicon tetrafluoride. The gravimetric procedure is described in most textbooks of quantitative analysis, e.g., Hillebrand,l Treadwe11 and Ha112 and Scott.3 Gravimetric procedures as ordinarily performed are not sufficiently sensitive for the accurate determination of less than 5 mg of silica. Micro-gravimetric procedures based on similar chemical principles to the above, but with the apparatus and techniques of Emich4 and Pregl,5 have been described by Morgan and King6 Gerstel7 and HolL8