Giovanni Piccardi

Geochemical surveillance of active volcanoes: data on the fumaroles of Vulcano (Aeolian Islands, Italy)

Temperature and chemical composition of condensates of higher temperature fumaroles, located on the rim of the crater of Vulcano, were studied over a period of one year.Maximum temperature changed from 216°C (June 1977) to 291°C (May 1978).HCl is the main constituent of condensates which, in comparison with data from fumaroles of other volcanoes, contain also noteworthy quantities of boron and bromine.Since these chemical characteristics suggested the possible inflow of water of marine origin into the volcanic conduit, experimental data on seawater-rock reactions at high temperatures and pressures were taken into account.A model is drafted for the volcanic system, in which the occurrence of an aquifer interposed between the magma chamber and the surface is considered.The vaporization of this aquifer would feed the fumaroles giving rise, through different mixing processes with surface waters, to the observed differences in temperature and chemical composition. However, data available at present are not sufficient to support the proposed model, which must be mainly considered as a working hypothesis.

Analysis of snow from Antarctica: a critical approach to ion-chromatographic methods

Ion-chromatographic methods for anion and cation determination in snow samples from Antarctica are evaluated with regard to sensitivity and selectivity. An eluent-step change method is proposed to determine simultaneously mono- and divalent cations with detection limits lower than 1 μg/L. Special attention is given to the determination of the ammonium ion at trace levels in the presence of high sodium concentrations and the problems of sample contamination by the laboratory environment are evaluated. Two alternative methods, one using isocratic and the other a gradient elution, are proposed for the determination of fluoride, acetate, formate and methanesulphonate ions. Both methods are discussed to evaluate their use in snow sample analysis.

A chronocoulometric investigation of the methylene blue—Methylene blue leucoform system in phosphate buffer on mercury

Abstract The methylene blue—methylene blue leucoform (MB—MBL) system in a pH 7.9 aqueous phosphate buffer has been studied on mercury by the single-step chronocoulometric technique. It has thus been shown that at −0.050 V/SCE, where MB is still electroinactive, a gradual increase in the MB bulk concentration cO* beyond 10−8 M causes the progressive formation of an adsorbed monolayer of MB molecules in direct contact with the electrode. At cO*=2.5×10−6 M this monolayer is complete and a further increase in cO* causes the formation of a second adsorbed monolayer of MB at the top of the first. The potential at which the first adsorbed monolayer is electroreduced is positive with respect to the formal potential E0=−0.250 V of the MB/MBL couple and shifts towards more positive values with an increase in cO*, for cO* both less and greater than 2.5×10−6 M. The positive shift for cO* 2.5×10−6 M, namely when the first adsorbed monolayer is already complete.

Spectrophotometric determination of noble metals with tin(II) in bromide solutions

Abstract In presence of tin(II) bromide, noble metals give coloured products which are suitable for spcctrophotometric determinations. The colours are red (platinum), yellow-orange (rhodium), yellow-brown (palladium), yellow (iridium) and violet (gold) They are extracted, except for gold, with isoamyl alcohol Platinum, rhodium and palladium can be separated from irdium, and rhodium and platinum from palladium. Rhodium and platinum can be determined simultaneously.

The dissociation constant of I3− in the voltammetric behaviour of the iodine—iodide couple

Abstract The theoretical polarographic characteristic of the iodine—iodide system has been derived, taking into account the dissociation constant of I3−. The range of applicability of some approximate expressions has been determined. The agreement between the theoretical and experimental polarograms has been verified in acetonitrile and in aqueous 1 M HClO4.

Composition of hydrothermal fluids during the bradyseismic crisis which commenced at Phlegraean Fields in 1982

A systematic geochemical surveillance on the fumaroles of Solfatara and the boiling pools of Pisciarelli was carried out by discontinuous monitoring of the chemical composition of the emitted fluids during the Phlegraean Fields bradyseismic crisis which has begun in 1982. The fluids are considered to be produced by the ebullition of shallow aquifers receiving a convective gaseous inflow from the underlying magma chamber.Increased water vapor concentrations at a constant temperature of about 155 °C throughout the investigated period, along with the occurrence of ground deformations and seismic phenomena, are interpreted as resulting from an increased heat supply to the boiling water bodies.Dissolution processes and reactions with the confining rocks can alter the chemical composition of fluids escaping from magma to a large extent. Therefore it does not appear correct to consider the absolute values of any chemical constituent for geochemical surveillance without taking this modifying factor into account. Acid gases will be preferably absorbed by the above mentioned aquifers, while other species like H2, N2, O2, CH4, will instead increase their relative concentrations. Because of this, water vapour concentrations and the ratios H2S/CO2 and H2/CH4 in surface thermal manifestations appear to reflect better the varying extent of the observed phenomenon.On the basis of these parameters, and of both the upheaval rate and the intensity of seismic events, maximum values in the convective input of magmatic origin are estimated to have occurred at the beginning of the crisis and in September–October 1983.As long as water bodies at shallow depth are able to buffer the convective flow both thermally and chemically, no important volcanic activity can develop. When the absorbing capacity of these aquifers is exhausted, the increasing temperature and the changing characteristics of fluids towards a magmatic composition will indicate a higher probability of eruptive phenomena.

A detailed analysis of the polarographic behaviour of methylene blue in phosphate buffer on mercury

Abstract Polarographic current-potential characteristics and current-time curves for the reduction of methylene blue (MB) to methylene blue leucoform (MBL) in a pH 7.9 aqueous phosphate buffer have been examined in detail over a wide concentration range. It has thus been shown that the so called “normal” or “main” reduction wave of MB actually consists of two separate steps, the former with a half-wave potential practically coinciding with the formal potential E0=−0.250 V/SCE of the MB/MBL couple and the latter with a half-wave potential of about −0.310 V/SCE. As soon as the well-known MB adsorption prewave has attained its maximum height (which occurs at a MB bulk concentration c0*⋟5×10−5 M), a further slight increase in c0* causes the appearance of the wave with E1/2=−0.310 V. The height of the linear potential-sweep voltammetric peak corresponding to the latter wave increases proportionally to the sweep rate, thus revealing the “adsorption” nature of this wave. A comparison with a previous chronocoulometric investigation of the MB/MBL system has permitted us to conclude that the wave with E1/2=−0.310 V is due to reduction of the MB molecules which, after having reached the surface of the dropping electrode by diffusion, are adsorbed at the top of the adsorbed monolayer of MBL in direct contact with the electrode and remain in this adsorbed state after reduction. For c0*>7×10−5 M the wave with E1/2⋟E0=−0.250 V starts to develop. This wave is due to the electroformation of MBL molecules which diffuse back into the solution. The shape of polarographic current-potential characteristics and current-time curves has been accounted for semiquantitatively through an approximate solution of the corresponding diffusional problem.

Spectrophotometric determination of silicate in rain and aerosols by flow analysis

Abstract A flow analysis (FA) procedure for the measurement of soluble silicon with respect to the total Si concentration is described. After solubilization in H2O, in alkaline solutions or in concentrated HF, silicon is determined by the molybdenum blue spectrophotometric method. The effects of Si complexation by F− are considered as are the decomplexing capacities of H3BO3 or Al3+. The proposed method is applied to samples of rain and of aerosols on filters, collected in Florence. For both kind of samples, the water soluble silicon content is about 1% and practically independent of the total silicon content.

Concentration of peroxides and formaldehyde in air and rain and gas-rain partitioning

Rain and air of Florence have been collected in a continuous way andanalysed by flow analysis spectrofluorimetric methods for formaldehydeand hydrogen peroxide. Diurnal and seasonal variations were observed;the mean/maximum concentrations of all data (as μ gm−3) are 3.3/23.4 for HCHO and 0.4/4.93 forH2O2. The effect of external sources and ofphotochemical reactions produces periods of positive and negativecorrelations for these compounds. The mean/maximum rain concentration ofall data are 98/443 μ g l−1 for HCHO and 84/685 μg l−1 for H2O2. Concentrationratios rain/air and discrepancies to Henrys Law equilibrium arediscussed.

The fumaroles of Vulcano (Italy): differences in chemical compositions produced by the surface environment

Abstract The results of investigations carried out on volcanic gases during the Field Workshop held at Vulcano in September 1982 are reported. A brief description is given of the differentiated sampling and analytical procedures used for acid, condensable and non-condensable gases. The fumaroles at the crater are characterized by different temperatures but substantially uniform composition, indicating a common genetic process; in addition to gaseous species peculiar to a magmatic environment, waters of marine origin appear to be recycled into the feeding paths of these manifestations. The composition of the bubbling gases at the beach and in mud pools is considered to be the result of the flow of gaseous species of deep origin through shallow and surface aquifers; acid gases are preferentially absorbed and the concentrations of slightly soluble species, such as H 2 , N 2 , O 2 and CH 4 , are considerably enhanced.