Low Lead Content Research Articles

The lead content of pasture herbage

AbstractOn soils in north‐east Scotland derived from quite diverse parent materials, including granitic gneiss, sandstone, slate and mixed acidic and basic igneous rocks, the normal lead content of rotational mixed pasture herbage during the period of active growth is between 0·3 and 1·5 ppm in the dry matter. In autumn, at a date possibly determined by the cessation of active growth and therefore by climatic conditions, the lead content of the above‐ground portion of the plant begins to rise, reaching 10 pprn in late autumn, and may reach 30‐40 ppm in late winter or early spring before growth recommences. At this stage, young shoots with a low lead content appear and the senescent foliage withers away. The increase in lead content of the above‐ground portion when the plant is dormant may indicate movement from the root rather than active uptake of lead from the soil. The possibility of surface contamination by petrolengine exhaust fumes or other industrial materials has been ruled out, and soil contamination of the herbage cannot account for the effect observed. The level of lead in pasture herbage in late winter appears sufficiently high to justify consideration of possible effects on the health of the animal consuming appreciable quantities during this period.

Lead isotope abundance studies on mineral occurrences in the British Isles and their geological significance

Lead isotope abundances are reported for ninety-eight galena specimens from Great Britain and Ireland. The analyses were made with a solid-source mass spectrometer. Comparison analyses show excellent agreement with results from other laboratories using solid-source techniques, but differences of 1 to 5% may occur for individual abundances when comparison is made with laboratories utilizing the lead tetramethyl vapour technique. The model chosen for calculation of ages from the isotopic composition is that of Holmes and Houtermans, using the published values of Patterson for the isotopic comparison of primeval lead in iron meteorites and modern lead in ocean sediments. This model permits calculation of the parameters uranium-238/lead-204 and thorium-232/uranium-238 in the source of the ores, which may exhibit small regional differences. The Holmes-Houtermans model ages of three suites of galenas from south-west England, northern England and southern Norway give excellent agreement with published values of the absolute ages of genetically associated igneous rocks. Other models used for interpreting lead isotope abundances do not generally give such satisfactory agreement. The significance of the isotope data from Great Britain and Ireland is discussed regionally in terms of the age of mineralization as well as the possible correlation and origin of different deposits. Of the ninety-eight leads investigated, eighty-six are assumed to be normal and to obey the conditions of the Holmes-Houtermans model. The remaining twelve are B -type leads, as defined by Houtermans, i.e. the model ages are demonstrably older than the true age of mineralization. The main criteria for recognizing normal leads are, first, the close regional grouping of isotope abundances and, secondly, that the model age does not exceed the age of the enclosing sedimentary rocks on the basis of the most recently published geological time-scales of the fossiliferous strata. Detailed consideration of normal leads suggests the existence of six periods of mineralization in the British Isles, ranging in age from Lower Palaeozoic to Upper Mesozoic. The two most important and clearly defined groups are associated with the Caledonian and Hercynian orogenies, respectively. There is, as yet, no isotopic evidence for Tertiary mineralization in the British Isles. A discussion of the causes of normal lead isotope abundances indicates that the latter could be the result of large-scale crustal homogenization processes in continental geosynclinal-orogenic belts. However, there is not enough critical evidence to identify definitely the source of normal lead ores with either crust or mantle. B -type leads probably arise by comparatively localized remobilization and regeneration of lead from metamorphic basement complexes with high lead/uranium ratios, or low radiogenic lead content. The source of such leads frequently appears to be somewhat heterogeneous and ore solutions may not have the opportunity for extensive mixing before the site of deposition is reached. However, B -type leads in some cases give an approximation to the true age of the basement rocks from which they are derived. Processes of this type probably account for the 5-type leads in the north-west and central highlands of Scotland and in County Galway, western Ireland, where the occurrences are situated in metamorphic basement rocks. No cases have been definitely recognized within the British Isles in which lead has a negative, or anomalously young, model age ( J -type leads). The results presented in this paper do not support the view of Russell and co-workers that most vein-type deposits which have traversed sedimentary rocks exhibit J -type anomalies—a consequence of their suggestion that B -type leads, as defined by Houtermans, should be regarded as normal leads.

The polarographic determination of lead in tin-base alloys

A polarographic method for the determination of lead in tin-base alloys is described For alloys containing more than 2% lead no separations are necessary; in those with a lower lead content, most of the copper present must be removed as cupric oxide Results are exact: ±4% of the amount of lead present.

LOW‐LEAD, BRIGHT OPAQUE GLAZES AT CONES 08 TO 06*

AbstractThis investigation covered several systematic fields of opaque fritted glazes for cones 08 to 06 (1733° to 1841°F.) in which lead oxide was replaced by barium, strontium, and zinc oxides. All glaze ingredients except the kaolin and the Ultrox zirconium opacifier were incorporated in the frits. Glazes of low‐lead content as well as some lead‐free compositions were obtained which possessed excellent gloss and opacity on wall tile of low and of medium tale content. Barium oxide was the best substitute for lead oxide from the standpoint of gloss, although moderate amounts of strontium and zinc oxides can be used to advantage. The whitest and most opaque glazes were obtained with the use of zinc oxide.