Saturated paste extracts

Table 3.3. Concentrations of trace elements in soil solutions extracted by saturated paste from two metal salt-spiked Israeli soils incubated at the saturated paste regime...

Table 6.2. The original metal concentration (HN03-extractable) in native soils and levels of addition to the two Israeli arid soils incubated under the saturated paste regime condition ...

Figure 7.4. Comparisons of decreases in NH4N03-extractable Zn, Ni and Cu in an Israeli loessial soil receiving metal nitrates and incubated under saturated paste, field capacity, and wetting/drying cycle moisture regimes (Han and Banin, 1997,1999, and Han et al., 2001a)...

The major ion composition of dispersed soil solutions and saturation extracts from selected soils in California, U.S. Concentrations of trace elements in soil solutions of the California soils that received sludge applications. Concentrations of trace elements in soil solutions extracted by saturated paste from two metal salt-spiked Israeli soils incubated at saturated regime. 

For soil classification purpose the conductivity of saturation extracts of soils is required. However, extraction of solution from a saturated paste is very difficult process. As an approximation, the conductivity of the water extracts from a 1 2.5 soikwater suspension is determined and the conductivity of the saturation extract is calculated as EC (saturation extract) = E.C (1 2.5 extract) x 250/saturation percentage. 

Salinity defines the concentration of ions dissolved in soil water, and is measured directly by electrical conductivity (EC). Soil water is held under tension or suction and as such is not available for analysis. To compensate for this, the standard procedure is to measure soil EC on a water extract. Soil scientists use what is called a saturated paste soil water extract (for more details see Radojevic and Bashkin, 1999). 

The salinity may be determined directly as a total content of water-soluble salts, or as a sum of contents of particular ions. The measurement of the specific electric resistance of the soil is a very rough, but simple and rapid method. It is used for soil surveys on a wide scale. For achieving more precise results, it is possible to use a method standardized by measuring the resistance in saturated soil paste (the soil paste is prepared by mixing a soil sample with distilled water to obtain a moderately liquefied paste) and the results are corrected with respect to a temperature of 16°C. Tables are used to convert the measured electrical resistance values to the soil concentration. For more precise data, it is possible to separate the solution from the saturated soil paste and to measure the specific electric conductivity. The solution separated from the soil paste is called the saturated soil extract. 

The diazotization of the amines is carried out in the usual manner. The volume of water is kept at a minimum since the success of the reaction depends in part on the efficiency with which the unstable intermediate is extracted from the aqueous layer by the organic liquid. Either the previously prepared amine hydrochloride is employed or a paste of the hydrochloride is prepared by dissolving the amine in concentrated hydrochloric acid and then cooling rapidly with stirring. For diazotization a nearly saturated solution of sodium nitrite (1 g. in 2 cc. of water) is used. Little work has been done with very weakly basic amines in the diazo reaction.48 In one instance, the base, l-nitro-2-naphthylamine, was diazotized by means of nitrosylsulfuric acid in sulfuric acid benzene was added and then sodium hydroxide until the mixture was slightly alkaline.49 For the very weak bases, the nitrosoacetyl reaction is recommended, since it is carried out entirely under anhydrous conditions. 

These methods were selected for different reasons, but mainly for their flexibility and novelty. Rhizon samplers represent the current equivalent of porous cups, widely used in the recent past centrifugation is possibly the current most widely used method because of the ease and the ready availability of the requisite equipment in most laboratories squeezing is a novel alternative, since it has been used on soils recently (Di Bonito, 2005) and has the potential to access water contained in small pores soil suspension or saturation extracts constitute a valid alternative, especially when batch experiments are carried out (Degryse et al., 2003). Furthermore, these methods are capable to perform fractionated extraction on the soil, whereby a combination of the methods can be used to provide soil water originating from a wider range of pores, which can present a variety of interactions with the soil matrix and possibly different chemistry. 

Cover 0.5 g of cholesterol with 5 mL of acetic acid in a small Erlenmeyer flask, swirl, and note that the initially thin slurry soon sets to a stiff paste of the molecular compound C27H45OH CH3CO2H. Add 1 mL of acetic anhydride and heat the mixture on the steam bath for any convenient period of time from 15 min to 1 h record the actual heating period. While the reaction takes place, prepare the chromatographic column. Cool, add 20 mL of water, and extract with two 25-mL portions of ether. Wash the combined ethereal extracts twice with 15-mL portions of water and once with 25 mL of 10% sodium hydroxide, dry by shaking the ether extracts with 25 mL of saturated sodium chloride solution, then dry the ether over anhydrous sodium sulfate for 10 min in an Erlenmeyer flask, filter, and evaporate the ether. Save a few crystals of this material for TLC (thin-layer chromatography) analysis. Dissolve the residue in 3-4 mL of ether, transfer the solution with a capillary dropping tube onto a column of 12.5 g of silica gel, and rinse the flask with another small portion of ether. ... 

The traditional classification of salt-affected soils in the United States has been based on the soluble salt (EC) concentrations of extracted soil solutions and on the exchangeable sodium percentage of the assodated soil. The dividing line between saline and nonsaline soils was established at 4 dS m-1 for water extracts from saturated soil pastes. Salt-sensitive plants, however, can be affected in soil whose saturation extracts have ECs of 2 to 4 dS m l. The Terminology Committee of the Soil Science Sodety of America has recommended lowering the boundary between saline and nonsaline soils to 2 dS m-1 in the saturation extract. 

For electrochemical chloride extraction (abbreviated CE, also called chloride removal, or desalination), a direct current is applied between the reinforcement (cathode) and an anode that is placed temporarily on the outer surface of the concrete. The anode is an activated titanium wire mesh or a reinforcing steel mesh. The anode is surrounded by tap water or saturated calcium hydroxide solution in ponds (upper, horizontal surfaces) or tanks (vertical or overhead surfaces) or as a paste that can be sprayed onto all types of surface. Chloride ions migrate from the reinforcement to the anode. Due to a relatively high current density of 1 to 2 A/m, relatively large amounts of chloride can be removed from the concrete within a relatively short time, usually 6 to 10 weeks. After that, the anode, the electrolyte and the incorporated chloride ions are removed from the stracture. The principle layout and electrode reactions involved are indicated in Figure 20.8. 

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