Calcium anhydrous

E2 Iodine products calcium anhydrous calcium iodate hexahy-... 

Drying of crystals. Whenever possible crystals should be dried in a smdl vacuum desiccator containing a suitable desiccant. The latter depends upon the nature of the solvent used c/. p. 19). However for most purposes anhydrous calcium chloride is satisfactory. If a hydrocarbon has been used in the recrystallisation, a few thin fresh shavings of paraffin wax are efficacious. 

Lead formate separates from aqueous solution without water of crystallisation. It can therefore be used for the preparation of anhydrous formic acid. For this purpose, the powdered lead formate is placed in the inner tube of an ordinary jacketed cond ser, and there held loosely in position by plugs of glass-wool. The condenser is then clamped in an oblique position and the lower end fitted into a receiver closed with a calcium chloride tube. A current of dry hydrogen sulphide is passed down the inner tube of the condenser, whilst steam is passed through the jacket. The formic acid which is liberated... 

Both forms sublime very readily, even at room temperature a small sample on exposure to the air will completely volatilise in a short time, particularly on a warm day or if the sample is exposed to a gentle current of air. Hence the above method for rapid drying. A sample confined in an atmospheric desiccator over calcium chloride rapidly disappears as the vapour is adsorbed by the calcium chloride. A sample of the hexahydrate similarly confined over sodium hydroxide undergoes steady dehydration with initial liquefaction, for the m.p. of the hydrated-anhydrous mixture is below room temperature as the dehydration proceeds to completion, complete resolidification occurs. 

Calcium Chloride. Dissolve 100 g. of CaCl2,6H20 (or 50 g. of anhydrous CaClj) in water and make up to i litre. 

Another valuable drying agent of general application is anhydrous calcium sulphate, marketed under the name of Drierite. It is rapid in its action, but has only a limited drying capacity because it forms the hydrate 2CaS04,H20 and thus combines with only 6-6 per cent, of its weight of water. The vapour pressure of the system ... 

Two forms of the so called calcium chloride tubes (also termed drying tubes, straight form) are shown in (c) and (d) these are fiUed with anhydrous calcium chloride or with cotton wool (previously dried at 100°), and are attached by means of a stopper to a flask or apparatus containing substances from which moisture is to be excluded. 

Fig. 77,13, 1 illustrates a distillation unit when it is desired to protect the distillate from moisture in the atmosphere. The drying tube may be filled with anhydrous calcium chloride held in position by loose plugs of glass wool or with a loose plug of cotton wool. Fig. 77,13, 2 depicts the use of an air condenser for liquids of boiling point above 140-150°. 

The beat method of drying, if time permits, is to place the crystals in a desiccator containing an appropriate substance (usually anhydrous calcium chloride, silica gel, or concentrated sulphuric acid) to absorb the solvent. More eflicient and more rapid drying is obtained with the aid of a vacuum desiccator (see Section 11,38 and Fig. 77, 38, 1). 

Anhydrous magnesium sulphate. This is an excellent, neutral desiccating agent and is inexpensive. It is rapid in its action, chemically inert and fairly efficient, and can be employed for most compounds including those (esters, aldehydes, ketones, nitriles, amides, etc.) to which calcium chloride is not applicable. 

Metallic sodium. This metal is employed for the drying of ethers and of saturated and aromatic hydrocarbons. The bulk of the water should first be removed from the liquid or solution by a preliminary drying with anhydrous calcium chloride or magnesium sulphate. Sodium is most effective in the form of fine wire, which is forced directly into the liquid by means of a sodium press (see under Ether, Section II,47,i) a large surface is thus presented to the liquid. It cannot be used for any compound with which it reacts or which is affected by alkalis or is easily subject to reduction (due to the hydrogen evolved during the dehydration), viz., alcohols, acids, esters, organic halides, ketones, aldehydes, and some amines. 

Alcohols Anhydrous potassium carbonate anhydrous magnesium or calcium sulphate quicklime. 

Alkyl halides Aryl halides Anhydrous calcium chloride anhydrous sodium, magnesium or calcium sulphate phosphorus pentoxide. 

Saturated and aromatic hydrocarbons Ethers Anhydrous calcium chloride anhydrous calcium sulphate metallic sodium phosphorus pentoxide. 

Aldehydes Anhydrous sodium, magnesium or calcium sulphate. 

In practice, it is best to purify a quantity, say one Winchester quart bottle, of technical 0 720 ether to cover the requirements of a group of students. The Winchester quart of ether is divided into two approximately equal volumes, and each is shaken vigorously in a large separatory funnel with 10-20 ml. of the above ferrous solution diluted with 100 ml. of water. The latter is removed, the ether transferred to the Winchester bottle, and 150-200 g. of anhydrous calcium chloride is added. The mixture is allowed to stand for at least 24 hours with occasional shaking. Both the water and the alcohol present are thus largely removed. The ether is then filtered through a large fluted filter paper into another clean dry Winchester bottle (CAUTION all flames in the vicinity must be... 

Di-teo-propyl ether. The commercial product usually contains appreciable quantities of peroxides these should be removed by treatment with an acidified solution of a ferrous salt or with a solution of sodium sulphite (see under Diethyl ether). The ether is then dried with anhydrous calcium chloride and distilled. Pure di-iao-propyl ether has b.p. 68-5°/760 mm. 

Higher alcohols. These may be purified by drying with anhydrous potassium carbonate or with anhydrous calcium sulphate, and fractionated after filtration from the desiccant. Bark corks (or ground glass joints) should be used rubber stoppers are slightly attacked. The boiUng points of the fractions to be collected are as follows —... 

Mono-alkyl ethers of ethylene glycol, ROCHjCHjOH. The mono methyl, ethyl and n-butyl ethers are inexpensive and are known as methyl cellosolve, cellosolve, and butyl cellosolve respectively. They are completely miscible with water, and are excellent solvents. The commercial products are purified by drying over anhydrous potassium carbonate or anhydrous calcium sulphate, followed by fractionation after... 

The acetone is refluxed with successive small quantities of potassium permanganate until the violet colour persists. It is then dried with anhydrous potassium carbonate or anhydrous calcium sulphate, filtered from the desiccant, and fractionated precautions are taken to exclude moisture. 

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