Downs cells

Dowicide A Dowicil 100 Dowicil 200 Dowlex resins Downs cell... 

Fig. 2. Downs cell A, the steel shell, contains the fused bath B is the fire-brick lining C, four cylindrical graphite anodes project upward from the base of the cell, each surrounded by D, a diaphragm of iron gau2e, and E, a steel cathode. The four cathode cylinders are joined to form a single unit supported on cathode arms projecting through the cell walls and connected to F, the cathode bus bar. The diaphragms are suspended from G, the collector assembly, which is supported from steel beams spanning the cell top. For descriptions of H—M, see text.

The cell bath in early Downs cells (8,14) consisted of approximately 58 wt % calcium chloride and 42 wt % sodium chloride. This composition is a compromise between melting point and sodium content. Additional calcium chloride would further lower the melting point at the expense of depletion of sodium in the electrolysis 2one, with the resulting compHcations. With the above composition, the cells operate at 580—600°C, well below the temperature of highest sodium solubiUty in the salt bath. Calcium chloride causes problems because of the following equiUbrium reaction (56) ... 

Lithium. Several processes for lithium [7439-93-2], Li, metal production have been developed. The Downs cell with LiCl—KCl electrolyte produces lithium ia much the same manner as sodium is produced. Lithium metal or lithium—aluminum alloy can be produced from a mixture of fused chloride salts (108). Granular Li metal has been produced electrochemically from lithium salts ia organic solvents (109) (see LiTHlUM AND LITHIUM compounds). 

Sodium metal is produced commercially on the kilotonne scale by the electrolysis of a fused eutectic mixture of 40% NaCl, 60% CaCh at 580°C in a Downs cell (introduced by du Pont, Niagara Falls, 1921). Metallic Na and Ca are liberated at the cylindrical steel cathode and rise through a cooled collecting pipe which allows the calcium to solidify and fall back into the melt. Chlorine liberated at the central graphite anode is collected in a nickel dome and subsequently purified. Potassium cannot be produced in this way because it is too soluble in the molten chloride to float on top of the cell for collection and because it vaporizes readily... 

Edgar The larva is a fully functional animal made up of terminally differentiated cells, but its purpose is to be an incubator for these imaginal discs that make the fly. It has to bulk up on mass and it transfers this biomass to the discs as they grow. I think it is a really simple way for an organism that is already differentiated to grow. It is a sort of stripped-down cell cycle that can respond to nutrition. There is no need for those cells to proliferate. 

Elemental chlorine is produced by the electrolysis of molten NaCl in the Downs Cell. The other product is sodium metal. The products must be separated because the reaction between metallic Na and gaseous Cl2 is very rapid, spontaneous and explosive. The product, Cl2, is poisonous. 

Preparation. Li is currently produced by electrolysis of molten LiCl, the melting point of which (614°C) is lowered by addition of KC1. The salt mixtures used (not very different from the eutectic one) contain about 45-55 mass% LiCl the electrolysis is carried out at 400-460°C. The cells commonly used resemble the cell used for the production of sodium (Downs cells). 

Preparation. Sodium can be produced by electrolysis of a mixture of NaCl (40%) and calcium chloride, CaCl2 (60%), melting at about 580°C. The electrolysis is carried out as a melt in a Downs cell , producing also calcium metal as well, which is solidified in a collection pipe and returned back to the melt. Since 1950 a modified Downs cell has been used with an electrolyte consisting of a ternary mixture of NaCl, BaCl2 and CaCl2. 

The large cell used for the electrolysis of sodium chloride in industry is known as a Downs cell. To decrease heating costs, calcium chloride is added to lower the melting point of sodium chloride from about 800°C to about 600°C. The reaction produces sodium and calcium by reduction at the cathode, and chlorine by oxidation at the anode. 

Some metals are extracted in electrolytic cells. In section 11.3, you saw the extraction of sodium from molten sodium chloride in a Downs cell. Other reactive metals, including lithium, beryllium, magnesium, calcium, and radium, are also extracted industrially by the electrolysis of their molten chlorides. 

O Most industrial reactions take place on a much larger scale than reactions in a laboratory or classroom. The voltage used in a Downs cell for the industrial electrolysis of molten sodium chloride is not very high, about 7 V to 8 V. However, the current used is 25 000 A to 40 000 A. Assuming a current of 3.0 x 10 A, determine the mass of sodium and the mass of chlorine made in 24 h in one Downs cell. Express your answers in kilograms. 

You have already seen that chlorine gas can be made by the electrolysis of molten sodium chloride. In industry, some chlorine is produced in this way using the Downs cell described earlier. However, more chlorine is produced in Canada using a different method, called the chlor-alkali process. In this process, brine is electrolyzed in a cell like the one shown in Figure 11.32. Brine is a saturated solution of sodium chloride. 

Write a descriptive paragraph to compare the reactions that occur in a Downs cell and a chlor-alkali cell. Describe the similarities and differences. 

To subculture cells, resuspend the cells by pipetting the cells up and down to break down cell clusters. Count the cells using a hemocytometer. 

A the growth medium containing the ketone 1 and optically active alcohol (R)-2 from the first step was added to spun down cells of Y. lipolytica for the second reduction step ... 

Gas gangrene Clostridium perfringens Clostridia toxin Activates phosphohpase to break down cell membranes. (Major cause of death in First World War and American Civil War)... 

Sodium is produced by an electrolytic process, similar to the other alkali earth metals. (See figure 4.1). The difference is the electrolyte, which is molten sodium chloride (NaCl, common table salt). A high temperature is required to melt the salt, allowing the sodium cations to collect at the cathode as liquid metallic sodium, while the chlorine anions are liberated as chlorine gas at the anode 2NaCl (salt) + electrolysis —> Cl T (gas) + 2Na (sodium metal). The commercial electrolytic process is referred to as a Downs cell, and at temperatures over 800°C, the liquid sodium metal is drained off as it is produced at the cathode. After chlorine, sodium is the most abundant element found in solution in seawater. 

Cell microarrays have also been fabricated. Ziauddin and Sabatini (2001) demonstrated the ability to transfect cells cultured onto plasmid DNA arrayed in gelatin on a standard DNA microarray slide. Xu (2002) printed down cells in the form of high density microarrays on permeable membranes and demonstrated phenotypic assay performance with the immobilized cells. The commercialization of viable cell arrays will permit an even closer look at cell-mediated events during the drug discovery process. 

Since predators of snakes (and humans) have to deal with snake venoms as defenses, they are included here, even though they serve in predation. Snake venoms are primarily enzymes (proteins), especially of the phospholipase A2 type, which breaks down cell membrane phospholipids hydrolytically. Other snake venoms such as cobrotoxin contain peptides with 60-70 amino acid residues. Pharmacologically, they have neurotoxic, cytotoxic, anticoagulant, and other effects. The neurotoxins, in turn, can have pre- or postsynaptic effects. Snake venoms with both neurotoxic and hemolytic effects on the heart are known as cardiotoxins. Cytotoxins attach to the cells of blood vessels and cause hemorrhage. Snake venom factors may stimulate or inhibit blood clotting. Finally, platelet-active factors can contribute to hemorrhage. 

Sodium was first isolated by Sir Humphry Davy in 1807 by electrolysis of caustic soda. In the following year. Gay Lussac and Thenard obtained metallic sodium by chemical reduction of caustic soda with iron at elevated temperatures. Deville, in 1854, prepared the metal by reduction of sodium carbonate and lime with charcoal at a temperature above the boiling point of sodium. Castner, in 1886, improved the chemical reduction process preparing the metal by heating sodium hydroxide with iron carbide at high temperature. Five years later he patented a process based on electrolytic reduction of sodium hydroxide. The first major commercial plant was set up in 1921 with the introduction of Downs cell. 

There are two electrolytic methods that are of major importance. One involves the electrolysis of fused sodium chloride using the Downs cell. This method currently is most prevalent. The Downs cell consists of a steel cell with brick lining containing the fused bath. The multiple electrode arrangement consists of four cylindrical graphite anodes that project upward from the hase of the cell. Each anode is surrounded hy a diaphragm of iron gauge and a steel cathode. 

Electrolysis of fused sodium hydroxide has heen achieved successfully with a Castner cell. The Castner cell was used in commercial production prior to introduction of Downs cell. The cell is operated at a bath temperature 320 10°C, at 9.0 0.5 amp current and a voltage of 4.3 to 5.0 V. The cathode current density is about 10.9 kA/m2. The cell consists of a copper cathode and a nickel anode and a cylindrical iron-gauge diaphragm placed between the electrodes. The cell reactions are as follows ... 

Some T cells become cytotoxic cells and track down cells Infected with viruses... 

Downs cell A cell used for electrolyzing molten sodium chloride. 

FIGURE 18.16 Cross- sectional view of a Downs cell for commercial production of sodium metal by electrolysis of molten sodium chloride. The cell design keeps the sodium and chlorine apart so that they can t react with each other. 

---