Re-solution and effervescence

The first point for consideration in this two-stage model is the re-solution of the gas phase. We use CH4 as an example. 65 m CH4 (STP) occupies 1 m at a depth of 700 m (68 atm and 310 K). From Price (1981), 14.6 m CH4 (STP) saturates 10 m of pure water under these. -40 m of pure water, unsaturated with respect to CH4, are therefore required to re-dissolve this gas (more if this were a brine). If this volume is air-equilibrated water, the additional (and unfractionated) noble gas content would have the effect of lowering the final °Ne/ Ar fractionation value to F = 1.57, less than the maximum fractionation value predicted for a single stage equilibrium. Notwithstanding more complex processes, such as the addition of a phase with no initial noble gas content, it would seem that the 

If the fluid in equilibrium with the final gas phase is air-equilibrated water, the concentration of fractionated noble gases in solution must be significantly higher than 

T = 310 K Salinity = 5M NaCl K MkAr = 2.33x103 atm Kj MkNe = 4 72xio5atm 

The limits imposed by closed system interaction between water, gas and oil phases on the range of the gas phase °Ne/ Ar ratios, originally derived from the air-equilibrated water, can be assessed (Bosch and Mazor 1988). For example at 310 K, Knb and Kat are 8471 atm kg/mol and 4155 atm kg/mol respectively in a 5M NaCl brine, and K nc and K° Ar are 622 atm Kg/mol and 117 atm Kg/mol. Maximum positive Ne/Ar fractionation in a gas phase occurs when the oil phase equilibrates with a small volume of water, transferring the noble gas content of the water into the oil phase with minimal fractionation. Subsequent equilibration of the oil with a small volume of gas will produce a fractionation value of F(Ne/Ar)gas = 622/117 = 5.3 (Eqn. 21), compared with the maximum fractionation of F(Ne/Ar)gas = 8471/4155 = 2.03 predicted for a water/gas system under the same conditions (Fig. 7a). Maximum gas phase Ne/Ar fractionation, in the opposite direction, occurs when the oil phase equilibrates with a large volume of water to produce F(Ne/Ar)oii = (117/4155)/(622/8471) = 0.31 (Eqn. 23). 

The addition of one extra phase, crude oil, to a gas/water system more than doubles the range of fractionation that can occur in any associated gas phase, from between F(Ne/Ar)gas = 1.0 to 2.03 to between F(Ne/Ar)gas = 0.31 to 5.3. In the case of an open system, fractionation in the residual phase will be even more extreme, and reflected in much lower concentrations (Battani et al. 2000). While it is possible to envisage a myriad of different interactions between water, gas and oil phases, depending on the order of interaction, open or closed system behavior and the relative fluid volumes, it is not a 

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Subsurface fluid phases with high noble gas concentrations as well as noble gas fractionation in excess of single step phase fractionation limits may provide field evidence for multi-stage processes of re-solution and effervescence. 

Both the physical re-solution of the major gas phase and also the large mass of the fluid phase required appear to preclude resolution and effervescence as a significant mechanism to fractionation noble gases beyond the soluble equilibrium limit without very careful consideration of the geological context. 

Extract the combined ether extracts with small quantities of N sodium bicarbonate until the last extract is colourless. Combine the bicarbonate solutions, add ether and acidify with 5N hydrochloric acid. When effervescence has ceased, shake to extract, run off the aqueous layer and filter the yellow ether layer into a graduated flask. Dissolve any brown residue in sodium hydroxide solution as before, re-acidify and repeat the extraction with 20 ml of ether. Continue to extract in this way, with 20-ml quantities of ether, until extraction is complete and then dilute the combined extracts to volume with ether. 

The fi-compound is dissolved in 50 c c. pure dry ether, and dry hydiogen chloride is passed in with constant shaking to prevent the delivery tube from becoming blocked. Colourless crystals of the hydrochloride of the /3-o ime separate and aie filtered and washed with dry ether and then placed in a separating funnel and covered with a layer of ether. A. concentrated solution of sodium carbonate is gradually added with constant shaking until no further effervescence is observed. Sodium chloride is precipitated and the /3-oxime dissolves in the ether. The ether extract is sepaiated, dehydrated over sodium sulphate, and the ether remoi ed as rapidly as possible at the ordinary temperature by evaporation in vacuo. The residue crystallises, and when pressed on a porous plate leaves a mass of small silky needles, m. p. 126—130A It may be re-... 

The effect of temperature on reaction rates can be demonstrated with two tablets of effervescent antacid, two cups, and tap water. Into one cup, place a half cup (120 milliliters) of cool tap water from the faucet. In the other cup, place an equal amount of hot tap water from the faucet. Drop one tablet into each cup at the same time. The fizzing action is clearly more vigorous in the hot water than in the cool water. In this case, the higher temperature helps in two ways. It forces more bubbles out of solution (which is the same reason you re cautious about opening a warm can of soda), and it increases the reaction rate because molecules at a higher temperature move around faster, find each other more often, and hit each other harder when they do. This effect and other principles concerning chemical kinetics is the subject of the following discussion. 

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