Contents Precipitation

Abstract Based on long-term and seasonal data, the basic hydrometeorological features that form the natural regime of the Black Sea are under consideration, which include climate (regional atmospheric circulation, winds, atmospheric pressure, air temperature, moisture content, precipitation), wind waves, water balance, sea level (multiannual and seasonal changes, storm surges, seishes, tidal oscillations), as well as sea ice. 

The [aMo03-aNiMo04 ] catalysts with a ratio RA=0.83 or 0.25 were chosen as references. The effect of bismuth content (precipitation) and of the water were studied. 

Schematic of grain boundary region in a 2XXX alloy. Precipitation of the very-high-copper-content precipitates on the boundary causes a copper-depleted zone on either side of the boundary. The difference in the electrochemical potentials of the copper-depleted zone and the copper-rich matrix form a strong galvanic cell with a potential difference of about 0.12 V. Furthermore, the anodic copper-depleted zone is small in area compared with the area of the cathodic grain matrix, resulting in a high driving force for rapid intergranular corrosion. (Courtesy of Alcoa Technical Center, Edward L. Colvin.)...

In a general view we can separate a coastal group with high ionic content precipitation including Salvador, Rio de Janeiro, Niteroi, Cubatao, Vila Parisi and Santos, and an interior group with low ionic content precipitation comprising Sao Paulo, Sao Jose dos Campos and the Amazon. 

Liquid chromatography is preceded by a precipitation of the asphaltenes, then the maltenes are subjected to chromatography. Although the separation between saturated hydrocarbons and aromatics presents very few problems, this is not the case with the separation between aromatics and resins. In fact, resins themselves are very aromatic and are distinguished more by their high heteroatom content (this justifies the terms, polar compounds or N, S, 0 compounds , also used to designate resins). 

The asphaltene content is found either directly by precipitation using n-heptane (NF T 60-115 or ASTM D 32), or indirectly by correlation with the Conradson Carbon. It can vary from 4 or 5% to as much as 15 or 20% in extreme cases. 

The conversion to lighter products is limited by the asphaltenes content (C insolubles). At high conversions, the residual asphaltenes —no longer being soluble in their environment— tend to precipitate, resulting in the production of unstable residues that are unmarketable. 

Triturate 20 g. of dry o-toluidine hydrochloride and 35 5 g. of powdered iodine in a mortar and then grind in 17 -5 g. of precipitated calcium carbonate. Transfer the mixture to a conical flask, and add 100 ml. of distilled water with vigorous shaking of the flask. Allow the mixture to stand for 45 minutes with occasional agitation, then heat gradually to 60-70° for 5 minutes, and cool. Transfer the contents of the flask to a separatory funnel, extract the base with three 80 ml. portions of ether, diy the extract with anhydrous calcium chloride or magnesium sulphate, and remove the excess of solvent. The crude 5-iodo-2-aminotoluene separates in dark crystals. The yield is 32 g. Recrystallise from 50 per cent, alcohol nearly white crystals, m.p. 87°, are obtained. 

After 5 hours the reaction is stopped and the flask cooled. The formyl-MDA can be isolated and hydrolyzed by any of the ways Strike just mentioned a few paragraphs back, but this method offers a third, very convenient way which should be tried. What the chemist does is forget about letting the flask and its contents cool. Instead, she removes the oil bath, places the flask back on the stirplate (distillation setup still attached), attaches a vacuum and distills off all the formamide. What remains is a dark, heavy formyl-MDA precipitate that is allowed to cool down while the chemist makes up a solution of 150g potassium hydroxide (KOH), 500mL ethanol and 125mL dH20. This solution is poured into the... 

Besides pH, other preparative variables that can affect the microstructure of a gel, and consequendy, the properties of the dried and heat-treated product iaclude water content, solvent, precursor type and concentration, and temperature (9). Of these, water content has been studied most extensively because of its large effect on gelation and its relative ease of use as a preparative variable. In general, too Httie water (less than one mole per mole of metal alkoxide) prevents gelation and too much (more than the stoichiometric amount) leads to precipitation (3,9). Other than the amount of water used, the rate at which it is added offers another level of control over gel characteristics. 

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