Variations in the acid content of rain water in the course of a single precipitation

The major acid components in the rain water collected during five different rainfall events in July and August 1977, were found to be a strong acid, the weak acid NH _in4 ^su+ and dissolved CO₂ from the atmosphere. Variations in their concentrations were determined as a function of time in the course of each of the rainfall events. Two experimental methods were used in this investigation, a microtitrim etric method and a coulometric method, and the data were analyzed by the use of modified Gran functions. Both methods gave the same results. The most significant observation was that the strong acid concentration increased from very low values to a maximum and then decreased in the course of a single rainfall event.     

Zacatecas (Mexico) Companies Extract Hg from Surface Soil Contaminated by Ancient Mining Industries

In Zacatecas, Mexico, four plants are operating to extract Ag, Au, and Hg using CaS₂O₃ solution from surface soil containing tailings from the amalgamation method used during 1550–1900. The metal ions extracted are cemented by scrap Cu wires. Hg is separated by evaporation from the cemented amalgam and Ag and Au are obtained from the residue. A part of the soil to be leached was separated and leached as in the industrial process. Only 121 ppm of Hg was freed from 168 ppm of extractable Hg. About a half of the remaining Hg in the soil evaporated during 18 months. This confirms that the Hg in the soil is metallic. Pb and As are also freed in the same process. It is estimated that 13 000–34 000 t of Hg had been discarded in the extraction of Ag.