Part 103
=Chloral, Hydrate.= C_{2}HCl_{3}O. Aq. _Syn._ HYDRATE OF CHLORAL. _Prep._ "Pass dry chlorine gas, for several days, through absolute alcohol, sp. gr. 0·795, until it becomes a thick viscid liquid of sp. gr. 1·57. At the beginning of the operation the alcohol is well cooled to prevent inflammation and explosion, but towards the end of the operation the alcohol is heated nearly to the boiling point. The resulting liquid, which after a day or two solidifies to a mass of crude chloral hydrate, is agitated with four times its bulk of concentrated sulphuric acid, and the anhydrous chloral which floats on the surface is separated and purified by fractional distillation. The purified anhydrous chloral is placed in a still, mixed with 11 per cent. of water, and distilled over chalk to remove any hydrochloric acid that may be present; the resulting solid distillate is then fused and poured out into shallow vessels to cast into cakes." (Squire.) The purest chloral hydrate is said to be that which has been crystallised two or three times out of pure bisulphide of carbon.--_Prop._ White opaque solid, having a pungent odour resembling that of a ripe melon. Soluble in water, glycerin, and alcohol. Gradually volatilises in the air, and may be distilled without decomposition. From 100 gr. dissolved in 1/2 fl. oz. of water, well shaken with 1 fl. oz. of solution of potash (B. P.), and allowed to stand for several hours, at least 46 grain-measures of chloroform should separate.
Chloral hydrate may be obtained in crystals by mixing the cake with about half its bulk of chloroform, and putting aside in a cool place. When the crystallisation is complete (which is generally in about 8 or 10 days) the crystals are freed from the mother liquor by a centrifugal machine, and afterwards dried at a gentle heat. The mother liquor may be utilised for future crystallisations.
_Uses._ An excellent sedative, antispasmodic, hypnotic, anodyne. It has done good service in hypochondriacal and other nervous affections, as well as in the insomnia of the insane, and of dipsomaniacs; also in asthma, hooping-cough, and scarlet fever. It has also the reputation of being an efficient preventive of sea-sickness, especially on short voyages, such as crossing the channel, which can be accomplished during the sleep occasioned by the agent.--_Dose_, from 10 to 60 gr.
It was introduced into medical practice by Dr Liebreich, of Berlin. Immense quantities are imported into this country from Germany.
=CHLORALUM.= An impure aqueous solution of chloride of aluminum, sp. gr. 1·15, 1 fl. oz. of the liquid contains 75 grains of anhydrous chloride. Introduced by Professor Gamgee as an antiseptic and disinfectant, for which purposes it is recommended to dilute the article as sold with four times its bulk of water.
=CHLO''RATE.= _Syn._ HYPEROXYMU''RIATE[dagger], CHLO''RAS, L. A compound in which the hydrogen of chloric acid, HClO_{3}, is replaced by a metal or other basic radical, _e.g._ KClO_{3}, chlorate of potassium. Chlorates may be prepared by dissolving the hydrate or oxide in chloric acid, and crystallising. The alkaline chlorates, however, are made by passing chlorine into solutions of the hydrate or carbonate of potassium or sodium, boiling the resulting liquid, and separating the chlorate from the chloride, which is also formed by crystallisation. They are very similar to the nitrates, both in their general properties and composition. They are all decomposed at a red heat, metallic chlorides being formed and oxygen gas given off. Like the nitrates, they deflagrate with inflammable substances, but with greater facility and violence. A mixture of this kind will detonate with a slight blow or friction. All the chlorates are soluble in water.
_Char., Tests, &c._ The chlorates are known by their deflagrating when placed on red-hot charcoal. By evolving a yellow gas when treated with concentrated sulphuric acid, in the cold, which gas also communicates to the liquid a red or yellow tinge. By evolving oxygen gas when heated alone in a test-tube. This test is not characteristic, unless carried a stage further, by dissolving the residual chloride out of the tube, and adding to the filtered solution a few drops of nitrate of silver; then the formation of a white precipitate, insoluble in nitric acid, will show that the salt treated was a chlorate, and not a nitrate. Pure chlorates give no precipitate with nitrate of silver.
=CHLORHY'DRIC ACID.= See HYDROCHLORIC ACID.
=CHLO''RIC ACID.= HClO_{3}. _Syn._ HYPEROXYMURIAT'IC ACID; ACIDUM CHLO''RICUM, L. An acid discovered by Chenevix, but first obtained in a separate form by Gay-Lussac.
=CHLO''RIDE= (-[)i]d). _Syn._ CHLO''RURET[dagger]; CHLORI'DUM, L. A chemical compound of chlorine with a metal or other basic radical, _e.g._ NaCl, chloride of sodium; C_{2}H_{5}Cl, chloride of ethyl.
_Prep._ The majority of the metallic chlorides may be made by simply dissolving the metal or its carbonate, oxide, or hydrate, in hydrochloric acid (previously diluted with about twice its weight of water), and evaporating and crystallising the solution in the usual manner. Zinc, cadmium, iron, nickel, cobalt, and tin, dissolve readily in hydrochloric acid; copper only in strong boiling acid; silver, mercury, and gold, not at all. The insoluble chlorides, as those of silver and mercury, may be readily prepared by precipitating any of their corresponding soluble salts with hydrochloric acid, or a soluble chloride, such as common salt. Anhydrous chlorides are generally prepared by the direct action of chlorine on the bases.
_Char., Tests, &c._ Most of the metallic chlorides are soluble in water. Many fuse when heated, and volatilise unchanged, but others are completely or partially decomposed at a red heat. All, with the exception of those of the alkali and earth metals, are decomposed at a red heat in a current of hydrogen. They are recognised by the following reactions:--1. Heated with a little peroxide of manganese and sulphuric acid, chlorine is evolved, and easily detected by its colour, smell, and bleaching properties:--2. The soluble chlorides may be readily detected by their solutions, slightly acidulated with nitric acid, giving with a solution of nitrate of silver a white, curdy precipitate (chloride of silver), insoluble in nitric acid, freely soluble in liquor of ammonia, and blackened by the light:--3. The insoluble chlorides may be tested by digesting them in a little liquor of potassa, when a solution of chloride of potassium will be formed, which may be treated as just directed (2); or the chloride may be dissolved in nitric acid, and tested with nitrate of silver as before.
=CHLORIM'ETRY.= See CHLOROMETRY.
=CHLORINA'TED LIME.= See LIME.
=CHLORINA'TED SO'DA.= See SODIUM.
=CHLO''RINE.= _Syn._ CHLORIN'IUM, L.; CHLORE, Fr.; CHLOR, Ger. An elementary substance discovered by Scheele in 1774, and at first supposed to be a compound body. In 1809 MM. Gay-Lussac and Thénard suggested the probability of it being a simple substance; but it was reserved for Sir H. Davy, shortly afterwards, to demonstrate the truth of the suggestion of these foreign chemists.
_Nat. Hist._ It exists in nature chiefly in the form of chloride of sodium, which constitutes rock salt when deposited in inland beds, sea salt when dissolved in masses of water. The sea also contains chlorides of potassium, calcium, and magnesium. It is a constituent of several well-known minerals. It has been met with in the air of volcanic districts, combined with hydrogen, as hydrochloric acid.
_Prep._ Strong hydrochloric acid is poured on half of its weight of finely-powdered peroxide of manganese, previously placed in a glass flask or retort; chlorine gas is immediately evolved, even in the cold, but much more rapidly on the application of a gentle heat, and is collected in clean, dry bottles by displacement. The tube conducting the gas is so arranged as to reach to the bottom of the bottle, and the chlorine, being heavier than the air, displaces the latter without mixing with it. The bottle is known to be full by the gas, easily perceived by its green colour, overflowing the top of the vessel. The bottle is then closed up with an accurately fitting stopper, previously greased, and an empty one put in its place, which is subsequently treated in like manner. To free the gas entirely from hydrochloric acid it is passed through a wash bottle containing a small quantity of water; and to render it quite dry it is passed over fused chloride of calcium. When the presence of moisture is no object chlorine may be collected over warm water, or, what is better, a saturated solution of common salt, in the pneumatic trough. The mercurial trough cannot be employed, as the chlorine rapidly acts upon the metal, and becomes absorbed.
_Commercial._--From oil of vitriol and water, of each 7 parts, cautiously mixed, and allowed to cool; chloride of sodium (common salt), 4 parts, mixed intimately with peroxide of manganese, 3 parts. The dilute acid is placed in a retort or other generating vessel, and the powder added. The gas comes off slowly at first, but the application of a gentle heat causes it to rush forth in large quantities. Of late years, owing to the general demand for bleaching agents, numerous new methods and suggestions for obtaining chlorine have been patented, of which the following are the most important.
1. Elliott. By this method the reconversion of the chloride of manganese to peroxide was attempted as follows:--The manganese residues left in the still are first heated to dryness. They are then roasted in a current of steam, the result being the formation of hydrochloric acid (which is condensed), and a residue consisting of a mixture of protoxide and peroxide of manganese.
2. Gatty. In this process the manganese residues, after evaporation to a suitable consistence, are mixed with nitrate of soda, and the nitrate of manganese and chloride of sodium formed, when dried, are strongly heated in an iron retort, the fumes of nitric acid which come off being employed in the manufacture of sulphuric acid. The residue in the retort, consisting of peroxide of manganese, being lixiviated, yields the peroxide in a pure state:
Mn(NO_{3})_{2} + 2(NaCl) + O_{2} = MnO_{2} + 2NaCl + 2(NO_{3}).
3. Hoffman. This process consisted in the regeneration of the manganese by means of soda waste. In this process the chloride of manganese is, by the addition of the yellow ley obtained from the lixiviation of soda waste, converted into sulphide of manganese. The precipitate so obtained consists of
Sulphide of manganese 55·00 Sulphur 40·00 Protoxide of manganese 5 ------ 100·00
This is dried and then calcined, the sulphurous acid evolved being conducted into the sulphuric acid chamber.
The residue, which has the following composition--
Sulphate of manganese 44·50 Peroxide of manganese 18·90 Protoxide of manganese 36·60 ------ 100·00
--is next mixed with nitrate of soda and heated to 300° C., yielding sulphate of soda and nitrate of manganese, the latter, however, being at once decomposed into peroxide of manganese, and nitrogen peroxide, thus:--
_a._ MnSO_{4} + 2NaNO_{3} = Mn(NO_{3})_{2} + Na_{2}SO_{4}.
_b._ Mn(NO_{3})_{2} = MnO_{2} + 2NO_{2}.
After the mass has cooled, the sulphate of soda is washed out, the residue yielding, according to the inventor, a material equal to native peroxide of manganese.
4. Schlösing. Manganese is acted upon with a mixture of hydrochloric and nitric acids, the degree of concentration of the acids being so regulated by the addition of water that the mixture yields only chlorine, whilst protonitrate of manganese is formed; this salt being calcined yields peroxide of manganese and nitric acid. The nitric acid aids the oxygen of the air in decomposing the hydrochloric acid.
The following equation will explain the successive stages of the reaction:--
_a._ 2HCl + 2HNO_{3} + MnO_{2} = Cl_{2} + Mn(NO_{3}) + 2H_{2}O.
_b._ Mn(NO_{3})_{2} = MnO_{2} + 2NO_{2}.
_c._ 2NO_{2} + H_{2}O + O = 2HNO_{3}.
5. Vogel. By decomposing chloride of copper by heat. The chloride in the crystalline state is mixed with half its weight of sand and heated in earthenware retorts to 200° to 300° C., yielding chlorine gas, while the remaining protochloride of copper is reconverted into perchloride by the action of hydrochloric acid.
According to Laurens the reaction is as follows:--
_a._ 2CuCl_{2} = Cl_{2} + 2Cu_{2}2Cl_{2}. _b._ Cu_{2}Cl_{2} + 2HCl + O = H_{2}O + 2CuCl_{2}.
6. MacDougal, Rawson, and Shanks. This is effected by decomposing chromate of lime by means of hydrochloric acid, the result being the formation of chloride of chromium, chloride of calcium, and the evolution of free chlorine; thus
2CaCrO_{4} + 16 HCl = Cr_{2}Cl_{6} + 2CaCl_{2} + 8H_{2}O + Cl_{6}
158 parts of chromic acid yield 106 parts of chlorine. The chloride of chromium is again precipitated with carbonate of lime, and by ignition converted into chromate of lime. Only three eighths of the chlorine contained in the hydrochloric acid is given up, whilst manganese yields one half.
7. Hargreaves proposes to evaporate a solution of protochloride of iron to dryness, and then to heat the dried substance in a current of air, at a temperature of about the melting point of zinc, by which means perchloride of iron and free chlorine would be obtained. Thielbierge's suggestion consists in passing air over protochloride of iron, and so giving rise to peroxide of iron and chlorine. This, like Hargreaves' proposition, possesses the disadvantage of furnishing the chlorine very largely diluted with air and nitrogen.
8. Jessie de Mothney. This chemist has proposed a continuous process which is as follows:--Peroxide of manganese either alone or mixed with lime is put into a retort, which, when heated to redness, has a current of hydrochloric acid gas passed into it. A disengagement of chlorine and steam takes place, and there remains in the retort a mixture of undecomposed peroxide of manganese with chlorides of manganese and calcium. The retort containing the undecomposed peroxide and chlorides being still kept at a red-heat, air or oxygen is passed over them, the result being that the manganic chloride is decomposed at once.
The chlorine liberated by this last operation is conveyed into vats containing a mixture of lime and manganous oxide, which substances have been previously formed by the decomposition of the manganous chloride by lime, the soluble chloride of calcium having been run off. Sesquioxide of manganese and hypochlorite of calcium are formed in the vats, and these two, reacting on each other, give rise to peroxide of manganese and chloride of calcium. With fresh hydrochloric acid this latter product yields more chlorine for use in the chambers. Magnesia may be substituted for lime.
9. Dunlop. This process, which may be regarded as the first practical method for utilising the whole of the exhausted manganese residues, and rendering them capable of reapplication in the production of chlorine, was devised by Mr Dunlop in 1855, since which time it has been in use in the alkali works of the Messrs Tennant, at St. Rollox, Glasgow. The operation consists in precipitating the chloride of manganese in the still liquor by carbonate of calcium; the resulting manganese carbonate being decomposed by heat. The liquors are previously mixed with a little milk of lime, which frees them from ferric oxide, alumina, and silica.
Being allowed to stand until these and all other insoluble matters are precipitated, the clear solution containing the chloride of manganese is mixed with finely divided chalk, when the following reaction ensues:--
MnCl_{2} + CaCO_{3} = MnCO_{3} + CaCl_{2}.
The resulting milky liquid is then run into large iron boilers, through each of which passes horizontally an iron shaft furnished with a number of projecting arms. This shaft having been put into revolution so as to keep the contents of the boilers agitated, steam is admitted into them under a pressure of from two to four atmospheres, and by the combined effects of heat and pressure the decomposition of the manganese chloride by the calcium carbonate is accomplished in about four hours. The manganese carbonate is then allowed to subside, the calcium chloride solution is drawn off, the precipitate carefully washed, and thrown up in heaps on an inclined surface to drain. When partially dried the carbonate of manganese is placed in small low wagons, made of sheet-iron, supported on rollers, and slowly drawn through a furnace by means of a chain. The furnace holds forty-eight of these little wagons. The furnace is 50 feet long, 12 feet wide, and 10 feet high. "A fire-brick flue runs down the centre of the bottom of the furnace, and is connected at the far end with two return metal pipes, which lie on each side of the flue. A uniform heat at about 660° F. is maintained in the furnace, in which four lines of rails are laid for the small wagons to run along. The half-dried substance loses all its moisture and part of its carbonic acid as the wagons pass along the first line of rails, and as they return down the second line a further escape of carbonic acid ensues, and eventually the expulsion of all the acid, and the peroxidation of the manganese is completed during the passage of the wagons on the third and fourth lines." The operation lasts about forty-eight hours, the substance gradually changing in colour from white to brown, and lastly to black.
The ends of the furnace are closed by loose hanging doors, so as to ensure the entrance of a sufficient supply of air. The fire-place is situated below the floor of the furnace, and requires very careful watching. The resulting product is a mixture of oxides of manganese, and contains about 72 per cent. of peroxide of manganese.
9_a._ A. Dunlop. Another process designed by Mr Dunlop, and also in use at Messrs Tennant's, is as follows:--Nitrate of sodium (Chilian nitre) and chloride of sodium are decomposed by being heated in cast-iron cylinders with sulphuric acid. The gaseous products are made to pass through leaden Woulff's bottles containing sulphuric acid, which absorbs the nitric peroxide formed, and allows the passage of the chlorine into the chambers. The reaction may be represented by the following equation:--
NaCl + NaNO_{3} + H_{2}SO_{4} = Cl + NO_{2} + Na_{2}SO_{4} + H_{2}O.
The sulphuric acid charged with nitric peroxide is used in the manufacture of chamber acid.
10. Weldon. _a._ The process by which the greater part of the chlorine employed in the manufacture of bleaching compounds is now obtained and which has hitherto proved the most practical is that of Mr Walter Weldon. We have the authority of Mr Kingzett, in his work on 'The Alkali Trade,' for the statement, that out of 90,000 tons of bleaching powder made in Great Britain in 1874, 50,000 were procured by Weldon's method; and turning to the Continent we find the process largely adopted in Germany, France, and Belgium. The utilisation and regeneration of the residual product left in the still after the evolution of the chlorine which it will be presently seen is accomplished by the above process, is not the only advantage accruing from it, since it has also been the means of removing an extensive source of contamination of many of our streams and rivers, into which the then useless chloride of manganese was thrown previous to Mr Weldon's invention. It is true that the only waste product formed in the course of the operations, viz., chloride of calcium, is got rid of by being run into the nearest waters, but it is stated by the Rivers Pollution Commission, beyond making these harder, no other objectionable effect is caused by it.
Mr Weldon's process is based upon the fact, that if protoxide of manganese be suspended in a solution of chloride of calcium, and an excess of lime be added, the protoxide will become readily converted into peroxide if air be forced into the liquor. It had long been known that it was possible to convert into a peroxide the protoxide of manganese obtained by treating the residual still liquors with an equivalent of lime, but all attempts to reduce this knowledge to practical account had proved unsuccessful until Mr Weldon attempted it.
Mr Weldon made the important discovery, that whilst protoxide of manganese is by itself, when treated in the wet way with air, only capable of being converted into peroxide, at the greatest, to the extent of one half; the addition to the protoxide so treated of a certain quantity of lime converted the whole of it into peroxide in less than a twentieth the time required to peroxidise half the protoxide if lime were absent. It will be seen that it is the employment of an _excess_ of lime which constitutes the success of Mr Weldon's process, which is as follows:--
The residual liquors remaining in the still after the chlorine has been evolved by the action of hydrochloric acid on peroxide of manganese, and in which chloride of manganese is by far the predominating constituent, are run into a receptacle termed the _neutralising well_, which is usually six feet in depth by twenty in diameter. In this well the free hydrochloric acid of the still-liquor is neutralised by the addition of limestone or chalk, which at the same time serves to decompose the soluble ferric and aluminic chlorides present in the liquid, and to precipitate them as insoluble oxides. During this process the contents of the well are kept in a state of brisk agitation by means of a suitable stirrer. After this treatment the now neutral liquor consists of chlorides of manganese and calcium in solution, of a small quantity of suspended ferric and aluminic oxides and chalk. It additionally contains also in suspension a by no means small quantity of sulphate of lime, derived from the sulphuric acid always present in varying amount in the commercial hydrochloric acid used.
From the neutralising well the liquor is pumped to a height of some forty feet into tanks, called the _chloride of manganese settlers_, in which after from two to four hours it deposits the solid matters suspended in it, the supernatant clear liquor assuming a pale rose-coloured appearance.
The next operation is to draw off by means of syphons, which can be lowered or raised in the settlers to any desired level, this clear liquid, containing the chlorides of manganese and calcium, into a vessel called the _oxidizer_; this latter being an iron cylinder, of from eight to twelve feet in diameter, and from twenty-two to thirty-five feet deep. Two pipes go down nearly to the bottom of the oxidizer; the larger one being used for conveying a blast of air from a blowing engine, and the smaller for the injection of steam. The introduction of steam is only had recourse to in case the liquor when drawn into the oxidizer should not have the requisite temperature, viz. 130° or 140° Fahr. Immediately above the oxidizer a reservoir containing milk of lime is placed. A great deal depends upon the careful preparation of the milk of lime, since on the degree of fineness in which the lime is added to the manganese chloride in solution depends the rapidity with which it acts in the oxidizer. The milk of lime is kept constantly agitated, to ensure its being of uniform consistency, and should contain from 15 lbs. to 20 lbs. of hydrate of lime in every cubic foot of the mixture.