Immersion freezing

Add 101 g. (55 ml.) of concentrated sulphuric acid cautiously to 75 ml. of water contained in a 1 htre beaker, and introduce 35 g. of finely-powdered wi-nitroaniline (Section IV,44). Add 100-150 g. of finely-crushed ice and stir until the m-nitroaniUne has been converted into the sulphate and a homogeneous paste results. Cool to 0-5° by immersion of the beaker in a freezing mixture, stir mechanically, and add a cold solution of 18 g. of sodium nitrite in 40 ml. of water over a period of 10 minutes until a permanent colour is immediately given to potassium iodide - starch paper do not allow the temperature to rise above 5-7° during the diazotisation. Continue the stirring for 5-10 minutes and allow to stand for 5 minutes some m-nitrophenjddiazonium sulphate may separate. Decant the supernatant Uquid from the solid as far as possible. 

Place 130 ml. of concentrated hj drochloric acid in a 1 - 5 litre round-bottomed flask, equipped ith a mechanical stirrer and immersed in a freezing mixture of ice and salt. Start the stirrer and, when the temperature has fallen to about 0°, add 60 g. of finely-crushed ice (1), run in 47 5 g. (46 5 ml.) of pure aniline during about 5 minutes, and then add another 60 g. of crushed ice. Dissolve 35 g. of sodium nitrite in 75 ml. of water, cool to 0-3°, and run in the cold solution from a separatory funnel, the stem of which reaches nearly to the bottom of the flask. During the addition of the nitrite solution (ca. 20 minutes), stir vigorously and keep the temperature as near 0° as possible by the frequent addition of crushed ice. There should be a slight excess of nitrous acid (potassium iodide-starch paper test) at the end of 10 minutes after the last portion of nitrite is added. 

If the flow of cooling water is stopped while the apparatus is cold, the water may freeze and crack the immersion well. The vacuum jacket provides greater insurance against this problem than is available in the commercially available wells used with the usual 450 watt lamps. ... 

Cooling towers and evaporative condensers may freeze in winter if left operating on a light load. A common arrangement is to switch off the fan(s) with a thermostat, to prevent the formation of ice. The water-collection tank will have an immersion heater to reduce... 

Apart from such requirements for head pressure control, winter precautions are needed to prevent freezing of the water while the plant is not rejecting heat to it. These commonly take the form of an electric immersion heater in the water tank, together with lagging and possible trace heating of exposed pipes. In some systems, the evaporative condenser itself may be within the building, with air ducts to the outside. In severe climates, external tanks need to be lagged to conserve the heat provided by the immersion heater. 

The manufacture of ice in large blocks is by the can method (see Figure 12.1), where a number of mould cans, filled with water, are immersed to just below the rim in a tank of refrigerated brine. The smallest block made in this way is 25 kg and will freeze in 8-15 h, using brine at -11°C. Blocks up to 150 kg are made by this method. When frozen, the moulds are lifted from the tank and slightly warmed to release the ice block from the sides of the moulds, when they can be tipped out. Blocks may go into storage or for direct use. 

Poultry may be chilled for the fresh chicken market, or frozen. Chilling and freezing are mainly by cold air blast. Large birds such as turkeys are wrapped and immersed in low-temperature brine until the outside is well frozen, and then put into low-temperature storage to freeze right through. Some poultry is frozen by spraying with liquid carbon dioxide. 

Ice lollies are made from juice (water, sugar, citric acid, flavour and colour) and are frozen into shape using moulds immersed in a cold brine solution, in a similar manner to can ice making (see Section 12.4). The moulds are made from stainless steel or nickel, and pass in rows through a brine bath at - 45°C. Different layers of confection may be built up by allowing one outside layer to freeze, sucking out the unfrozen centre and refilling with another mix. The sticks are inserted before the centre freezes solid. The moulds finally pass... 

Material to be frozen can be fully immersed in a cold liquid. This might be a brine, in which case the material may have to be wrapped in a plastic bag to avoid contact with the liquid. The sodium chloride and glycol brines cannot be used cold enough to get complete freezing, so this may be a first pre-cooling stage before a final air blast. Alternatively, liquid nitrogen (- 196°C) or carbon dioxide (-78.5°C) can be sprayed onto the surface. 

Solid ozone is very expl, and at its freezing pt is very sensitive. If liq ozone in a tube is suddenly immersed to the full length of the ozone layer into solid nitrogen, detonation usually occurs. This probably is due to the fact that ozone crystals appear over the entire height of the tube, and by friction of one set of crystals against another, enough heat is developed to initiate ozone detonation. On the other hand, if only the bottom of the ozone tube is inserted into solid nitrogen, the crystallization of solid ozone proceeds slowly from the bottom toward the top and no detonation takes place (Ref 3, p 225)... 

A solution of 183 g. (1.10 moles) of triethyl phosphite (Note 1) in 200 ml. of petroleum ether (b.p. 30-60°) is added to a 3-1., three-necked, round-bottomed flask equipped with a mechanical stirrer, a thermometer, a dropping funnel, and an air condenser the open end of the condenser is connected to a drying tube filled with calcium sulfate or calcium chloride. The flask is immersed in a freezing mixture of sodium chloride and ice, and the stirrer is started. When the temperature of the phosphite solution reaches 0°, a solution of 273 g. (1.00 mole) of hexachlorocyclopentadiene (Note 2) in 100 ml. of petroleum ether (b.p. 30-60°) is added through the dropping funnel at such a rate that the temperature remains between 0° and 10°. The addition requires about 4-6 hours. After the addition is complete, the freezing mixture is removed, and the brown, clear solution is allowed to warm up to room temperature. 

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