Soda-lime

Soda lime eonsists of hydrated lime treated with caustic soda solution. It is used for absorbing carbon dioxide from air in medical, deep sea diving and military applications. It is manufactured by mixing hydrated lime with about 3 % of caustic soda and sufficient water to enable the paste to be extruded into pellets some 4 mm in diameter and 8 to 15 mm long. The pellets are then dried, screened and re-hydrated to a moisture content of about 20 %. 

The caustic soda dissolves in the free water and is the active component for the absorption of carbon dioxide at the surface of the pellet (32.8). The sodium carbonate so formed then reacts with calcium hydroxide to form calcium carbonate and regenerate sodium hydroxide (32.9). 

The hydrated lime should have a high active lime content and a particle size distribution that gives the paste the required rheological properties. It should be sound and not cause expansion in the pellets which could lead to low strength or dusting. 

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It is prepared by the action of sodium hydroxide and sodium hypochlorite on phthalimide (Hofmann reaction). When heated with soda lime it gives aniline. 

It gives benzene when heated with soda lime. It is very stable towards oxidizing agents. 

It is a dibasic acid, and forms stable metallic salts. Distillation with soda lime gives benzene. Readily dehydrated to phthalic anhydride. Its reactions are similar to phthalic anhydride in which form it is almost invariably used. 

Other methods for analyzing combustion products can be substituted for chromatography. Gravimetry can be used, for example, after a series of absorption on different beds, as in the case of water absorption in magnesium perchlorate or CO2 in soda lime infra-red spectrometry can be used for the detection of CO2 and water. 

It decomposes exothermically to oxygen, a reaction which can be explosive. Even dilute ozone decomposes slowly at room temperature the decomposition is catalysed by various substances (for example manganese(IV) oxide and soda-lime) and occurs more rapidly on heating. 

Fig 23(A) shows an assembly for boiling a liquid under reflux whilst adding another liquid at a rate which can be clearly seen cf. preparation of acetophenone, p. 253). The outlet A allows expansion of the vapour content, and can be fitted with a calcium chloride or soda-lime tube. The outlet A can also be used for collecting a gas evolved during the reaction cf, preparation of acetylene,... 

Chill the concentrated solution of the amine hydrochloride in ice-water, and then cautiously with stirring add an excess of 20% aqueous sodium hydroxide solution to liberate the amine. Pour the mixture into a separating-funnel, and rinse out the flask or basin with ether into the funnel. Extract the mixture twice with ether (2 X25 ml.). Dry the united ether extracts over flake or powdered sodium hydroxide, preferably overnight. Distil the dry filtered extract from an apparatus similar to that used for the oxime when the ether has been removed, distil the amine slowly under water-pump pressure, using a capillary tube having a soda-lime guard - tube to ensure that only dry air free from carbon dioxide passes through the liquid. Collect the amine, b.p. 59-61°/12 mm. at atmospheric pressure it has b.p. 163-164°. Yield, 18 g. 

The Soda- lime Test. Certain classes of nitrogenous organic compounds (e.g., amides, etc.) evolve ammonia when heated with soda-lime. In view of the limited application of this test, however, it may well be reserved for Section 3, where it is included with other compounds reacting with soda-lime. 

Mix about 0 2 g. of each of the following powdered substances with about i g. of powdered soda-lime, preferably by grinding in a small clean mortar. The odour of ammonia in the cold usually indicates an ammonium ... 

Heating the acids or their salts with soda lime eliminates the carboxyl group, volatile products being often detectable. 

Heating uith soda-lime. See Section 3, p. 3 7. test is particularly useful for providing evidence of ... 

Gives aniline on heating with soda-lime. 

Soda-lime H, CH, H, C,H, <—odoui r ofburnt sugar—> benzene phenol benzene styrene, benzene... 

Prepare the acetylating mixture by adding i volume of acetic anhydride to 4 volumes of pure anhydrous pyridine, and shaking thoroughly. Immediately before use, transfer the mixture to a clean dry burette having a welUfitting glass tap, and then close the top of the burette by means of a soda-lime tube. 

Sodium and potassium hydroxides. The use of these efficient reagents is generally confined to the drying of amines (soda lime, barium oxide and quicklime may also be employed) potassium hydroxide is somewhat superior to the sodium compound. Much of the water may be first removed by shaking with a concentrated solution of the alkali hydroxide. They react with many organic compounds (e.g., acids, phenols, esters and amides) in the presence of water, and are also soluble in certain organic liquids so that their use as desiccants is very limited... 

Ammonia. Small quantities of ammonia may be prepared with the aid of the apparatus depicted in Fig. II, 48,4. Concentrated ammonia solution (sp. gr. 0-88) is gently heated in the flask surmounted by an efficient reflux condenser. The gas is dried by passage through the tower which is loosely packed with soda lime or quicklime, and is then passed... 

An additional useful test is to distil the acid or its sodium salt with soda lime. Heat 0.5 g. of the acid or its sodium salt with 0 2 g. of soda lime in an ignition tube to make certain that there is no explosion. Then grind together 0-5 g. of the acid with 3 g. of soda hme, place the mixture in a Pyrex test-tube and cover it with an equal bulk of soda hme. Fit a wide dehvery tube dipping into an empty test-tube. Clamp the tube near the mouth. Heat the soda lime first and then the mixture gradually to a dull-red heat. Examine the product this may consist of aromatic hydrocarbons or derivatives, e.g., phenol from sahcyUc acid, anisole from anisic acid, toluene from toluic acid, etc. 

Upon warming with 10-20 per cent, sodium or potassium hydroxide solution, no ammonia is evolved (distinction from primary amides). The base, however, is usually liberated upon fusion with soda lime (see experimental details in Section IV,175) and at the same time the acyl group yields a hydrocarbon. Thus benz-p-toluidide affords p-tolu-idine and benzene. 

When distilled with soda lime (Section IV,175), nitriles yield some ammonia, but pass over, in part, unchanged. They are identified by the b.p. and by hydrolysis to, and characterisation of, the corresponding acid. 

Mercury. Upon heating a mixture of the compound with soda lime in a long test-tube, a bright metallic mirror and, finally, drops of mercury will form in the upper part of the tube if mercury is present. 

Preliminary indication of the presence of a phenol ester may be obtained by heating the compound with soda-lime esters of phenols and also aromatic hydroxy-acids usually give the phenol. (Likewise amides, Imides, nitriles, substituted hydrazines, uretheines, etc. eifiord ammonia.)... 

Platinum is a beautiful silvery-white metal, when pure, and is malleable and ductile. It has a coefficient of expansion almost equal to that of soda-lime-silica glass, and is therefore used to make sealed electrodes in glass systems. The metal does not oxidize in air at any temperature, but is corroded by halogens, cyanides, sulfur, and caustic alkalis. 

To prepare the standard pH buffer solutions recommended by the National Bureau of Standards (U.S.), the indicated weights of the pure materials in Table 8.15 should be dissolved in water of specific conductivity not greater than 5 micromhos. The tartrate, phthalate, and phosphates can be dried for 2 h at 100°C before use. Potassium tetroxalate and calcium hydroxide need not be dried. Fresh-looking crystals of borax should be used. Before use, excess solid potassium hydrogen tartrate and calcium hydroxide must be removed. Buffer solutions pH 6 or above should be stored in plastic containers and should be protected from carbon doxide with soda-lime traps. The solutions should be replaced within 2 to 3 weeks, or sooner if formation of mold is noticed. A crystal of thymol may be added as a preservative. 

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