Drying in General

Water and Loss on Drying In general, for compounds containing water of crystallization or adsorbed water, a limit test, to be determined by the Karl Fischer Titrimetric Method, is provided under the heading Water. For compounds in which the loss on drying may not necessarily be attributable to water, a limit test, to be determined by other methods, is provided under the heading Loss on Drying. 

Drying, in general, usually means removal of relatively small amounts of water from material. Evaporation refers to removal of relatively large amounts of water from material. In evaporation the water is removed as vapor at its boiling point. In drying the water is usually removed as a vapor by air. 

Pre-drying In general only if high demands on surface quality is required, forced-air drying cabinet, approx. 2 h at about 85-100 °C. Drying too abruptly can lead to material feeding difficulties. 

All glassware should be scrupulously clean and, for most purposes, dry before being employed in preparative work in the laboratory. It is well to develop the habit of cleaning all glass apparatus immediately after use the nature of the dirt will, in general, be known at the time, and, furthermore, the cleaning process becomes more difficult if the dirty apparatus is allowed to stand for any considerable period, particularly if volatile solvents have evaporated in the meantime. 

Method 2 (from the free amine). Dissolve 9 - 3 g. (9 1 ml.) of aniline in 10 ml. of glacial acetic acid diluted to 100 ml. contained in a 250 ml. beaker or conical flask, and add with stirring or shaking a solution of 6 5 g. of pure sodium cyanate in 50 ml. of warm water. Allow to stand for 30 minutes, then cool in ice, and allow to stand for a further 30 minutes. Filter at the pump, wash with water and dry in the steam oven. The resulting phenylurea is generally colourless and has a m.p. of 148° (i.e., is pure) the yield is 11 g. If the colour or the m.p. of the product is not quite satisfactory, recrj stallise it from boiling water (10 ml. per gram) as in Method 1. 

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. 

Acid Deposition. Acid deposition, the deposition of acids from the atmosphere to the surface of the earth, can be dry or wet. Dry deposition involves acid gases or their precursors or acid particles coming in contact with the earth s surface and thence being retained. The principal species associated with dry acid deposition are S02(g), acid sulfate particles, ie, H2SO4 and NH HSO, and HN02(g). Measurements of dry deposition are quite sparse, however, and usually only speciated as total and total NO3. In general, dry acid deposition is estimated to be a small fraction of the total... 

In handling, shipping, and storing DRI, care should be taken to avoid oxidation. Millions of tons of DRI in pehet and lump form have been shipped by barge, ocean vessel, tmck, and rad. The key to avoiding oxidation is simply to keep the material cool and dry. The chemical reactions involved have been well documented. In general, oxidation of DRI takes place in two forms reoxidation and corrosion (2). 

Dry chemistry tests are used for the assay of metaboHtes by concentration or by activity in a biological matrix. In general, reactive components are present in amounts in excess of the analyte being deterrnined to make sure that the reactions go to completion quickly. Other enzymes or reagents are used to drive the reactions in the desired direction (25). Glucose and cholesterol are the analytes most commonly measured. 

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