Normal arsenic

In the modern forensic chemistry laboratory (Figure B) arsenic is detected by analysis of hair samples, where the element tends to concentrate in chronic arsenic poisoning. A single strand of hair is sufficient to establish the presence or absence of the element. The technique most commonly used is neutron activation analysis, described in Chapter 19. If the concentration found is greater than about 0.0003%, poisoning is indicated normal arsenic levels are much lower than this. 

Commercial lead arsenate usually consists mainly of the monohydrogen arsenate, but may also contain the normal arsenate. It is in great demand as an insecticide (see p. 301). Many methods of manufacture are described in the patent literature,14 some of the more recent being as follows (1) Metallic lead and arsenious oxide are added to a concentrated solution of arsenic acid containing nitric acid 15 lead arsenate is precipitated, the concentration of the arsenic acid remaining constant. At intervals the precipitate is removed and the arsenic acid solution again treated. (2) A solution of a soluble arsenate is treated... 

Normally arsenic levels in soils and sediment are on average 6 mg/kg (e.g. Riedel and Eikmann, 1986 Dudka and Markert, 1992), but may be much higher, particularly in soils in the vicinity of smelteries, and other industries using arsenic as well as in agricultural soils where pesticides, herbicides and defoliants have been used (see below). 

Dissection of organs with normal arsenic levels for refrigerated storage and/or the subsequent analysis should be performed under strictly contamination-controlled working conditions with pre-cleaned knives and appropriate tools made from quartz, plastics, or titanium, preferentially on clean benches. These restrictions, of course, are not necessary... 

From the given detection iimits it is obvious that in the past neutron activation anaiysis (NAA) was the most promising method for basic studies (e.g. Heydorn, 1984). This is aiso reflected in the literature particularly for the quite low normal arsenic levels in human materials (see data and references for Table 2). Despite the fact that this method is less used at present routinely it still is valuable as a reference method, and particularly useful for the certification of reference materials as a multielement approach (Van Renterghem et al., 1992). 

In mammals, arsenic intake derives from food and drinking water, inspired air and absorption through the skin. The chemical form of arsenic and its solubility affect the absorption of the element in mammals and its transfer into the bloodstream. According to Leonard (1991), the normal arsenic content in human blood is about 4 ng/ml. However, an average arsenic value of 7.9 ng/ml and a range of 0.4-70.5 ng/ml were reported by Minoia et al. (1990), who analyzed blood samples of 470 healthy Italians. 

In general, the use of Pb-Sb alloys has some drawbacks such as enhancing water decomposition and lowering the tolerance to cold flow (positive plates grow during service life, and slow hardening). To overcome these drawbacks, the additives explored in the literature are normally arsenic, tin, and silver [2]. Regarding arsenic... 

This technique was applied in the early 1960s to a lock of hair taken from Napoleon Bonaparte (1769-1821) on St. Helena. Arsenic levels of up to 50 times normal suggested he may have been a victim of poisoning, perhaps on orders from the French royal family. More recently (1991), U.S. President Zachary Taylor (1785-1850) was exhumed on the unlikely hypothesis that he had been poisoned by Southern sympathizers concerned about his opposition to the extension of slavery. The results indicated normal arsenic levels. Apparently, he died of cholera, brought on by an overindulgence in overripe and unwashed fruit. 

The success of the Bart reaction when applied to nuclear- substituted anilines is often much affected by the pH of the reaction-mixture. Furthermore, the yields obtained from some m-substituted anilines, which under the normal conditions are usually low, arc considerably increased by the modifications introduced by Scheller, and by Doak, in which the diazotisation is carried out in ethanolic solution followed by reaction with arsenic trichloride in the presence of a cuprous chloride or bromide catalyst. 

In view of the high reactivity and sensitivity to oxidation of o-phenylone-diamine, the normal experimental conditions of the Skraup reaction are modified the condensation is carried out hi the presence of glycerol, arsenic acid solution and dilute sulphuric acid. 

Impurities in cmde metal can occur as other metals or nonmetals, either dissolved or in some occluded form. Normally, impurities are detrimental, making the metal less useful and less valuable. Sometimes, as in the case of copper, extremely small impurity concentrations, eg, arsenic, can impart a harmful effect on a given physical property, eg, electrical conductivity. On the other hand, impurities may have commercial value. For example, gold, silver, platinum, and palladium, associated with copper, each has value. In the latter situation, the purity of the metal is usually improved by some refining technique, thereby achieving some value-added and by-product credit. 

Instead of depending on the thermally generated carriers just described (intrinsic conduction), it is also possible to deUberately incorporate various impurity atoms into the sihcon lattice that ionize at relatively low temperatures and provide either free holes or electrons. In particular. Group 13 (IIIA) elements n-type dopants) supply electrons and Group 15 (VA) elements (p-type dopants) supply holes. Over the normal doping range, one impurity atom supphes one hole or one electron. Of these elements, boron (p-type), and phosphoms, arsenic, and antimony (n-type) are most commonly used. When... 

Elemental arsenic normally exists in the a-crystaUine metallic form which is steel-gray in appearance and britde in nature, and in the P-form, a dark-gray amorphous soHd. Other aHotropic forms, ie, yellow, pale reddish-brown to dark brown, have been reported (1), but the evidence supporting some of these aHotropes is meager. MetaUic arsenic, heated under ordinary conditions, does not exhibit a discrete melting point but sublimes. Molten arsenic can be obtained by heating under pressure. 

Although some changes occur in the melting furnace, cathode impurities are usually reflected directly in the final quaUty of electrorefined copper. It is commonly accepted that armealabiUty of copper is unfavorably affected by teUurium, selenium, bismuth, antimony, and arsenic, in decreasing order of adverse effect. Silver in cathodes represents a nonrecoverable loss of silver to the refiner. If the copper content of electrolyte is maintained at the normal level of 40—50 g/L, and the appropriate ratio of arsenic to antimony and bismuth (29) is present, these elements do not codeposit on the cathode. 

Inorganic ar senic normally occurs in two oxidation states As(V) and As(III). Arsenic (V) gives a significantly lower response than ar senic (III). For pre-reduction As(V) to the As(III) concentrated hydrochloric acid and potassium iodide/ascorbic acid reagents were used. As organoarsenic compounds do not react with sodium tetrahydi oborate, they were decomposed with a mixture of HNO and on a hot plate. 

In catalytic incineration, there are limitations concerning the effluent streams to be treated. Waste gases with organic compound contents higher than 20% of LET (lower explosion limit) are not suitable, as the heat content released in the oxidation process increases the catalyst bed temperature above 650 °C. This is normally the maximum permissible temperature to which a catalyst bed can be continuously exposed. The problem is solved by dilution-, this method increases the furnace volume and hence the investment and operation costs. Concentrations between 2% and 20% of LET are optimal, The catalytic incinerator is not recommended without prefiltration for waste gases containing particulate matter or liquids which cannot be vaporized. The waste gas must not contain catalyst poisons, such as phosphorus, arsenic, antimony, lead, zinc, mercury, tin, sulfur, or iron oxide.(see Table 1.3.111... 

Besides the thiocyanates, just mentioned, other 5-donor complexes which are of interest are the dialkyl sulfides, [MCl3(SR2)3], produced by the action of SR2 on ethanolic RhCl3 or on [IrClg] ". Phosphorus and arsenic compounds are obtained in similar fashion, and the best known are the yellow to orange complexes, [ML3X3], (M = Rh, Ir X = Cl, Br, I L = trialkyl or triaryl phosphine or arsine). These compounds may exist as either mer or fac isomers, and these are normally distinguished by their proton nmr spectra (a distinction previously made by the measurement of dipole moments). An especially... 

Investigations into the effects of arsenic and phosphorus in single-phase brasses on their susceptibility to intergranular attack and stress-corrosion cracking in seawater have shown that the normal addition of arsenic to... 

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