Laboratory distillation

Distilled laboratory water has a conductivity range of 0.5-3 pmho/cm. The conductivity of drinking water in the USA ranges from 50 to 1500 pmho/cm (APHA, 1998). Conductivity of groundwater varies depending on the concentration of dissolved solids. That is why total dissolved solids (TDS) content can be estimated from a conductivity measurement. We can approximate the TDS in milligram per liter (mg/1) by dividing the conductivity value in pS/cm by a factor of two. 

Today, apparatus having standard ground-glass joints is used almost exclusively in every organic laboratory and hence in every distillation laboratory (Tab. 1). An encyclopaedia of chemical laboratory apparatus including the G.D.R. standards has been edited by Telle [3]. 

For checking an existing vacuum lay-out it suffices to connect points pi — and d—l, respectively, by straight lines and to find the points of intersection of these lines with scale A. If the point of intersection of pi — is situated above that of d — I the vacuum installation is adequate. For more detailed calculations the reader is referred to the original paper [125]. A vacuum system constructed of 20 —30 mm I.D. glass tubing is in general satisfactory in distillation laboratories it may be built up... 

A form of com])ression manometer that is very convenient for use in the distillation laboratory is the rotatable manometer of Moser (Fig. 382). It has three measuring... 

Arrangement of a distillation laboratory, starting up distillation apparatus... 

Arrangement of a distillation laboratory (square type) with a well-ventilated room and a separate pump room (for legend, see Fig. 404)... 

Chapter 9 — Arrangement of a Distillation Laboratory Starting Up Distillation Apparatus... 

This technique involves boiling plant material in water. Volatiles evaporating alongside water vapor become liquid on the surface of a condenser and collect at a collecting vessel (florentine flask). Because of insolubility in water, essential oil floats on top or sinks to the bottom according to its density. Rose oil is obtained by water distillation. Laboratory-scale essential oil distillation equipment (clevenger apparatus) operates on this principle. 

Along the same lines, a distillation can be simulated by gas phase chromatography. As in a refinery, distillation in the laboratory is very often the first step to be carried out, because it gives the yields in different cuts gasoline, kerosene, etc., and makes further characterization of the cuts possible. 

This is the ASTM D 2892 test method and corresponds to a laboratory technique defined for a distillation column having 15 to 18 theoretical plates and operating with a 5 1 reflux ratio. The test is commonly known as the TBP for True Boiling Point. 

Used in virtually all organic chemistry analytical laboratories, gas chromatography has a powerful separation capacity. Using distillation as an analogy, the number of theoretical plates would vary from 100 for packed columns to 10 for 100-meter capillary columns as shown in Figure 2.1. 

In the distillation units for producing petroleum cuts, the curves are determined in the laboratory from samples taken at regular intervals. 

Nitric acid is prepared in the laboratory by distilling equal weights of potassium nitrate and concentrated sulphuric acid using an air condenser, the stem of which dips into a flask cooled by tap water. The reaction is ... 

On the industrial scale oxygen is obtained by the fractional distillation of air. A common laboratory method for the preparation of oxygen is by the decomposition of hydrogen peroxide. H Oj, a reaction catalysed by manganese(IV) oxide ... 

Pure water for use in the laboratory can be obtained from tap water (hard or soft) by distillation if water of great purity is required, distillation must be carried out in special apparatus, usually made of quartz, not glass or metal precautions must be taken to avoid any spray getting into the distillate. Water which is sufficiently pure for most laboratory purposes can, however, be obtained by passing tap water through cation-exchangers and anion-exchangers as described above, when the water is deionised . 

In the laboratory, bromine is prepared by oxidation of bromide ion the oxidation is carried out by mixing solid potassium bromide with manganese(IV) oxide and distilling with concentrated sulphuric acid ... 

The reaction is carried out in a lead retort one suitable for the laboratory can be made from a piece of lead piping, bent like a retort and closed at the shorter end. This is charged with fluorspar and the acid and heated, and the hydrogen fluoride is distilled into a polythene vessel. 

The term distillation is applied to vaporisation and subsequent condensation according to (i) it should also be applied to (ii) since it is really the liquid which is converted into vapour and is first formed by condensation. Strictly speaking, the term sublimation should be applied to changes according to (iii). However, in practice, a substance when heated may first melt and then boil, but on cooling it may pass directly from the vapour to the solid the process is then also called sublimation. Indeed the mode of vaporisation, whether directly from solid to vapour or through the intermediate formation of a liquid, is of secondary importance it is the direct conversion of vapour to solid which is really the outstanding feature of sublimation in the laboratory. 

Rubber stoppers are frequently employed in the laboratory in vacuum distiUation assemblies (compare Section 11,19) for distillations under atmospheric pressure bark corks are generally used. Many organic liquids and vapours dissolve new rubber stoppers slightly and cause them to swell. In practice, it is found that rubber stoppers which have been previously used on one or two occasions are not appreciably attacked by most organic solvents, owing presumably... 

The inflammable solvents most frequently used for reaction media, extraction or recrystallisation are diethyl ether, petroleum ether (b.p. 40-60° and higher ranges), carbon disulphide, acetone, methyl and ethyl alcohols, di-Mo-propyl ether, benzene, and toluene. Special precautions must be taken in handling these (and other equivalent) solvents if the danger of Are is to be more or less completely eliminated. It is advisable to have, if possible, a special bench in the laboratory devoted entirely to the recovery or distillation of these solvents no flames are permitted on this bench. 

Ether. The most satisfactory method for the removal of (diethyl) ether is either on a steam bath fed from an external steam supply or by means of an electrically-heated, constant-level water bath (Fig. 77, 5, 1). If neither of these is available, a water bath containing hot water may be used. The hot water should be brought from another part of the laboratory under no circumstances should there be a free flame under the water bath. It caimot be too strongly emphasised that no flame whatsoever may be present in the vicinity of the distillation apparatus a flame 10 feet away may ignite diethyl ether if a continuous bench top lies between the flame and the still and a gentle draught happens to be blowing in the direction of the flame. 

Time of distillation. For any column there is always an optimum time of distillation below which accuracy is sacrificed and above which the slightly improved separation does not justify the extra time taken. For most laboratory columns this will vary between 1 hour and 8-10 hours. 

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