The dissolution of synthetic magnetite, maghemite, hematite, goethite, lepidocrocite, and akaganeite was faster in HCl than in HClO4. In the presence of H+, the Cl− ion increased the dissolution rate, but the ClO4− ion had no effect, suggesting that the formation of Fe-Cl surface complexes assists dissolution. The effect of temperature on the initial dissolution rate can be described by the Arrhenius equation, with dissolution rates in the order: lepidocrocite > magnetite > akaganeite > maghemite > hematite > goethite. Activation energies and frequency factors for these minerals are 20.0, 19.0, 16.0, 20.3, 20.9, 22.5 kcal/mole and 5.8 × 1011, 1.8 × 1010, 7.4 × 107, 5.1 × 1010, 2.1 × 1010, 3.0 × 1011 g Fe dissolved/m2/hr, respectively. The complete dissolution of magnetite, maghemite, hematite, and goethite is well described by the cube-root law, whereas that of lepidocrocite is not.

De-tert-butylation of 2-tert-butylphenol was carried out over thermally-treated and acid-treated Jordanian bentonite clay samples. This reaction was found to follow first-order kinetics for all clay samples with different pretreatment procedures. The apparent rate constant, k, was also determined, and found to depend on the pretreatment. Thermal pretreatment at temperatures up to 250°C has an enhancing effect on surface acid sites. The total surface acidity (Ho <4.8) and the concentration of strong acid sites peaked at 250°C. Also, as a result, the maximum catalyst activity was obtained with samples treated at this temperature. Acid pretreatment with 0.10 M HCl, 1.0 M H2SO4 or 1.0 M H3PO4, followed by thermal treatment at 250°C produced the best enhancement effect on the surface acidity and catalytic activity.

Increasing the pH of the spray water to solubilize the weak acid herbicide nicosulfuron and then decreasing pH below its pKa so that it converts into a neutral form enhances biological activity under some conditions. The water-dispersible granule formulation of nicosulfuron starts as dispersed particles. Adding 1% wt/wt K3PO4 solubilizes nicosulfuron and increases its activity compared to its dispersion without base. The type of buffer and the surfactant HLB or hydrophilic lipophilic balance, a measure of the molecular balance of the hydrophilic and lipophilic groups, altered the activity of nicosulfuron. Adding 1% wt/wt K3PO4 increases the pH, and the optimum HLB ranged from 13 to 17 on large crabgrass. Adding 1% wt/wt H3PO4 reduces the pH and lowers the optimum HLB range from 10 to 14 on large crabgrass. Adding the acidic buffer converts the solubilized nicosulfuron into its neutral form and increases activity under some surfactant conditions. Thus, neutral nicosulfuron is more active with lipophilic surfactants, while ionic nicosulfuron is more active with hydrophilic surfactants. When tested on other species, low HLB surfactants are the most active at low pH. These results support the concept that the physicochemical properties of the herbicide, adjuvants, and weed species should be matched for optimum activity.

Bone growth and turnover results from the coordinated activities of two key cell types. Bone matrix is deposited and mineralised by osteoblasts and it is resorbed by osteoclasts, multinucleate cells that excavate pits on bone surfaces. It has been known since the early 20th century that systemic acidosis causes depletion of the skeleton, an effect assumed to result from physico-chemical dissolution of bone mineral. However, our own work has shown that resorption pit formation by cultured osteoclasts was absolutely dependent on extracellular acidification; these cells are inactive at pH levels above about 7·3 and show maximum stimulation at a pH of about 6·9. Bone resorption is most sensitive to changes in H+ concentration at a pH of about 7·1 (which may be close to the interstitial pH in bone). In this region pH shifts of <0·05 units can cause a doubling or halving of pit formation. In whole-bone cultures, chronic HCO3- acidosis results in similar stimulations of osteoclast-mediated Ca2+ release, with a negligible physico-chemical component. In vivo, severe systemic acidosis (pH change of about –0·05 to –0·20) often results from renal disease; milder chronic acidosis (pH change of about –0·02 to –0·05) can be caused by excessive protein intake, acid feeding, prolonged exercise, ageing, airway diseases or the menopause. Acidosis can also occur locally as a result of inflammation, infection, wounds, tumours or diabetic ischaemia. Cell function, including that of osteoblasts, is normally impaired by acid; the unusual stimulatory effect of acid on osteoclasts may represent a primitive ‘fail-safe’ that evolved with terrestrial vertebrates to correct systemic acidosis by ensuring release of alkaline bone mineral when the lungs and kidneys are unable to remove sufficient H+ equivalent. The present results suggest that even subtle chronic acidosis could be sufficient to cause appreciable bone loss over time.

The normal diet of most small passerines contains insufficient calcium for effective eggshell formation and birds must often forage specifically for calcium-rich items in the environment. It has been demonstrated that anthropogenic acid precipitation can significantly reduce levels of available calcium in soil and the abundance of calcareous items such as snail shells. Recent research in areas adversely affected by acid precipitation on Continental Europe has suggested that reduced calcium availability has resulted in an increased incidence of eggshell defects in small birds. In this paper we present data from one of the areas of the U.K. most severely affected by acid precipitation and where snail abundance (0.36 snails per m2) and exchangeable soil calcium levels (0.02 mg g−2) were very low: lower than values at sites in the Netherlands where severe eggshell defects occurred. The provision of supplementary calcium and the examination of eggshells, however, provided no evidence that blue tits Parus caeruleus were constrained in their ability to form effective eggshells as a result of calcium deficiency. We suggest that other factors, besides low calcium availability, may be contributory to the high incidence of eggshell defects seen in other areas.