Crystallization of potassium nitrate

Helt, J.E. and Larson, M.A., 1977. Effects of temperature on the crystallization of potassium nitrate by direct measurement of super-saturation. American Institution of Chemical Engineers Journal, 23(6), 822. 

When organic matter decays, say, in the soil of cattle yards and stables, ammonia and ammonium compounds are produced by the action of certain bacteria. If the soil be fairly dry, but not too dry, a white scum appears on the exposed surface. The scum is made up of small crystals of potassium nitrate and, after a time, if the soil be extracted with water and strained, the liquid, on evaporation, furnishes yellowish-brown crystals of crude nitre. The crude nitre can be purified by resolution and crystallization. The white efflorescence sometimes seen on the walls of stables, etc., is sometimes, though not always, due to the formation of nitrates in this way. 

Put 20 g. of potassium ferrocyanide in a 250-cc. Erlenmeyer flask, adding 30 cc. of water. Place the flask on the water bath and heat till the ferrocyanide dissolves. Add 35 cc. of nitric acid (sp. gr., 1.24) and continue heating until a test portion shows no blue color but a dark green precipitate when treated with ferrous sulfate. Let stand for a day or two and filter off the tarry impurities. Now neutralize with sodium carbonate, taking care that no excess is added. Warm and, when cool, add from one to two times the volume of alcohol (ethyl). Set the flask in a dry place for a day or two, after which the impurities (chiefly crystals of potassium nitrate) may be filtered off, and the nitro-prusside crystallized out. Sometimes two or three treatments with alcohol are necessary. In order to expedite the operation of evaporating down to crystallization, the solution may be evaporated by heating in a suction flask under reduced pressure. Quick crystallization increases the yield. The yield should be above 75 per cent. 

A mixture of 0.05 mole of a cobalt salt (14.5g of the nitrate or 12g of the chloride—both 6-hydrate) and 21g of potassium thiocyanate are heated in 30ml of water until solution is complete. The dark blue liquid is cooled in ice until crystallization of potassium nitrate or chloride is complete and then suction-filtered. The residue is washed repeatedly with 10ml portions of ethyl acetate until it is... 

F. Mareck also reduced nitric acid with zinc. E. Fremy reduced nitric acid with sulphur dioxide and J. L. Gay Lussac reduced aqua regia by stannous chloride. A soln. of stannous chloride in hydrochloric acid and some crystals of potassium nitrate, heated on a water-bath, gave off nitrous oxide gas. According to... 

The formation of this brown compound can advantageously be utilised as a method of detecting ferrous salts in the presence of other metals that would obscure the more usual ferricyanide reaction.2 The solution to be tested is mixed with an equal volume of concentrated sulphuric acid, and a crystal of potassium nitrate added. The last-named becomes surrounded with red-brown streaks of the nitroso compound. 

The flask and test-tube are filled with pure concentrated sulphuric acid to the heights indicated in the drawing. If the sulphuric acid becomes brown as the result of the introduction of traces of organic matter, a tiny piece of a crystal of potassium nitrate will destroy the color. 

Heat the filtrate from the potassium nitrate crystals to boiling and evaporate it to about two-thirds its original volume. (1) What is the compound that separates during the boiling Filter the hot solution rapidly. Save the filtrate. Press the crystals between filter papers. Examine them with a magnifying glass. (2) Do they resemble the crystals of potassium nitrate in appearance (3) Upon what fact does the separation of potassium nitrate from the other three substances in solution depend Examine the crystals that are deposited from the filtrate when it cools. (4) What are they ... 

Solubility op Mixed Crystals of Potassium Nitrate and Silver Nitrate in Water at 25°. 

From the urine.—Fresh urine is evaporated to the consistency of a syrup over the water-bath the residue is cooled and mixed with an equal volume of colorless HNO of sp. gr. 1.42 the-crystals are washed with a small quantity of cold H3O, and dissolved in hot HsO the solution is decolorized, so far as possible, without boiling, with animal charcoal, filtered, and neutralized with potassium carbonate the liquid is then concentrated over the water-hath, and decanted from the crystals of potassium nitrate which separate then evaporated to dryness over the water-bath, and the residue extracted with strong, hot alcohol the alcoholic solution, on evaporation, leaves the urea more or less colored by urinary pigment. 

Add NH4NO3 to about 100 mL of water cmd stir it until it dissolves completely. Pour the solution through a coffee filter into glass container that has potassium chloride (KCl) at the bottom. Gently heat the mixture, and stir the mature until all the KCl is dissolved, taking care not to tap the glass too much so that you crack it. Then put the container in the freezer for two hours. (The cold speeds up crystallization.) Crystals of potassium nitrate with the consistency of slush form at the bottom. Pour off the excess liquid to continue drying them. 

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