Arsenic Specific pressure

Francesconi, K.A., P. Micks, R.A. Stockton, and K.J. Irgolic. 1985. Quantitative determination of arsenobe-taine, the major water-soluble arsenical in three species of crab, using high pressure liquid chromatography and an inductively coupled argon plasma emission spectrometer as the arsenic-specific detector. Chemosphere 14 1443-1453. 

Accdg to Dunkle s Lecture delivered at Picatinny Arsenal on Dec.13, 1955, Hydro-dynamic Theory of Detonation , (Ref 78), utilizes the laws of conservation of mass, energy and momentum to derive certain relationship known as the "Rankine-Hugoniot Equation . There are five basic equations, of which. the first three are related to five variables pressure, specific volume, energy, detonation velocity and particle velocity... 

The pressure coefficient of resistance of arsenic is negative.1 Little 2 gives the specific resistance at 20° C. as 46,000 ohms and the temperature coefficient of resistance as -0-00435 per degree. 

Arsenic is oxidised, mainly to arsenious oxide, when heated in nitrous oxide 8 the reaction becomes appreciable at 250° to 270° C. and ignition occurs at 400° to 450° C. This reaction takes place specifically between arsenic and the nitrous oxide and is not due to reaction with oxygen after thermal decomposition of the nitrous oxide, as such decomposition does not occur below 400° C. and is very slight at 460° C. Nor does the reaction resemble that which occurs in oxygen, except that, like the reaction in the dark with the latter gas (see p. 47), it is a surface reaction. No chemi-luminescence is observed, however, and there is no upper critical oxidation pressure. At 360° C. the product contains at least 99 per cent, of pure arsenious oxide, and at 420° C. it contains about 5-8 per cent, of arsenic pentoxide. 

The arsenic concentrations of metamorphic rocks generally decrease with increased metamorphism (Ryan et al., 1996), 265. As temperatures increase, more arsenic volatilizes out of the rocks. Specifically, metamorphic rocks that formed at <45 km in an ancient subduction zone in California lost about 80-85 % of their arsenic as metamorphic temperatures and pressures increased from about 275 °C and. 5 kilobars (kb) to approximately 750 °C and 12 kb (Bebout et al., 1999). As discussed in Section 3.6.2, the volatilization of arsenic during metamorphism may be important in transferring the element from subduction zones back into the crust (Figure 3.2). 

Higher sensitivity for the specific detection of arsenic can be achieved by an increase of make up flow. In correlation with literature the optimum flow rate was found to be 150-190 ml/min. Hydrogen was applied as reagent gas for arsenic detection since it supports the dissociation of organoarsenic compounds and the excitation. Furthermore it protects the surface of the discharge tube from deposition of arsenic. Optimum results were achieved with an hydrogen pressure between 280 and 350 kPa. 

Three allotrope modifications are known. The stable form is the grey metallic modification with a sublimation temperature of 613°C. Melting is possible in closed tubes at 817°C and a pressure of 28 bar. The metallic allotrope exists in a crystalline (specific weight 5.73 g/cm ) and an amorphous form (specific weight 4.7-5.1 g/cm. The yellow crystalline and the black amorphous modifications are metastable and transform into the grey arsenic under the influence of light or heat. Arsenic is nontoxic in its elementary form [1-5]. 

---