Chapter II: BLEACHING of =Linen=:--Linen may be bleached in a similar way to (14)

_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.

A charge of the clear liquor having been drawn into the oxidizer, and raised if necessary to the requisite temperature, the blowing in of air is begun, whilst at the same time the milk of lime is run into the oxidizer as rapidly as possible, the flow of milk of lime being only discontinued when a sample of the filtrate drawn off, by means of a tap placed near the bottom of the oxidizer, ceases to give the manganese reaction when mixed with a solution of bleaching powder. This reaction consists in the production of a purple colour caused by the formation of permanganate of calcium. More milk of lime is then added, when the contents of the oxidizer are found to consist of a thin white mud, composed of a solution of calcium chloride, holding in suspension a mixture of protoxide of manganese and lime. The injection of air being continued the white mud rapidly becomes darker in colour, and soon changes into a thin black mud composed of solution of calcium chloride, holding in suspension certain compounds of peroxide of manganese partly combined with protoxide of manganese, but chiefly with lime, which compounds Mr Weldon terms "_manganites_." Mr Weldon suggests that the manganites so formed may be regarded as salts in which the basic radical is calcium or manganese, and the acid radical MnO_{3}; and may be represented by the formulæ CaMnO_{3}, and MnMnO_{3}; and possibly also CaMnO_{2} (MnO_{2})_{2}. "The quantity of lime which has to be put into the oxidizer before the filtrate from a sample of its contents ceases to yield the manganese reaction varies very considerably. Recently precipitated protoxide of manganese dissolves very appreciably in neutral solution of chloride of calcium, its solution therein comporting itself with reagents exactly like solutions of manganese salts. It dissolves also in solution of oxychloride of calcium, that is to say, in solution of chloride of calcium containing dissolved lime; its solution in oxychloride of calcium not giving the ordinary manganese reactions."

"Hence even if all portions of the lime added to the chloride of manganese in the oxidizer were capable of acting on chloride of manganese equally readily, manganese could not cease to be so in solution as to be detectible by ordinary reagents, until more than an equivalent of lime had been added--that is to say, until enough had been added not only to decompose all the chloride of manganese, but also to form a certain quantity of oxychlorate of calcium. It is never the case, however, that all portions of the lime used are capable of acting on the chloride of manganese with equal readiness. The lime used always contains a larger or smaller proportion of particles coarser than the rest, which coarser portions cannot of course act so rapidly as the finer ones; and as the decomposition of the chloride of manganese requires to be completed as quickly as possible, those portions of the lime which will not act upon it instantly are scarcely allowed time to act upon it at all.

"These coarser portions of the lime thus contribute very little to the decomposition of the manganese, though they afterwards dissolve completely in the hot solution of chloride of calcium, and then play their full part in the reactions which take place during the subsequent blowing. The proportion of lime which thus does not act on the chloride of manganese varies with the source of the lime, and with the manner in which it is prepared, so that the quantity of lime which has to be added to a charge of chloride of manganese liquor in the oxidizer, before the filtrate from a sample of the resulting mixture ceases to become coloured on the addition of solution of bleaching powder, varies from about 1·1 to 1·45 equivalent.

"The further quantity of lime which is added after that point has been reached is now usually so much as to raise the total quantity to about 1·5 to 1·6 equivalents, being from one half to six tenths in excess of the quantity which actually takes part in the decomposition of the chloride of manganese."[239]

[Footnote 239: 'Chemistry, Theoretical, Practical, and Analytical, as applied to the Arts and Manufactures,'--Mackenzie & Co.]

As previously stated, Mr Weldon found that if only so much lime is employed as is necessary to precipitate the manganese, not more than half the protoxide of manganese will be converted into the peroxide, and that even this result will be accomplished very tardily. And, as has been already mentioned, a greater and more rapid yield of protoxide can only be obtained by using a larger proportion of lime. Any excess, however, of lime over that absolutely required for the peroxidation of the protoxide of manganese must be sedulously avoided, since a superabundance of lime leads to the formation of compounds that are not readily peroxidised. Should such compounds be formed, it is necessary to destroy them, and this may be done by the addition of a fresh quantity of chloride of manganese. The objectionable compounds in question are lime and protoxide of manganese, which are known in the process under the name of "bases;" and the reason why it is desirable to prevent as much as possible their formation will become evident when it is remembered that they cannot furnish chlorine when treated with hydrochloric acid, but that they merely dissolve in this latter.

The injection of air into the oxidizer, which constitutes the blowing operation, varies from two to four hours.

The quantity required to be blown in is chiefly dependent upon the depth of the oxidizer, and upon the amount of protoxide of manganese contained in a given volume of the charge.

The greater the depth of this latter the more rapidly does the peroxidation take place; and the greater the number of molecules of protoxide in a given volume of the charge, the larger is the total surface presented to the action of injected air, and consequently the greater is the proportion of the oxygen absorbed.

"In one instance 175,000 cubic feet of air were blown in during five hours, and of the oxygen contained in this, 14·8 per cent. (equal to rather more than 4 cwt.) was absorbed in the production of 22 cwt. of peroxide of manganese."[240]

[Footnote 240: Weldon.]

The expenditure of mechanical power in forcing the air into the oxidizer averages between seven and eight horse-power for every 100 lbs. of peroxide of manganese obtained. In theory, to produce the quantity of chlorine contained in a ton of bleaching powder containing 37 per cent. of chlorine, 1020 lbs. of peroxide of manganese would be required; but it is found in practice that instead of this quantity of peroxide giving the above result, 1100 lbs. are needed.

"The consumption of lime averages 14 cwt. per ton of bleach. By this process 1 ton of bleach is made, using 2832 lbs. of hydrochloric acid, generated by the decomposition of 47·5 cwt. of salt, viz. a quantity which theoretically yields 3334 lbs. of hydrochloric acid. There is therefore a loss of acid of 15 per cent. The loss of manganese varies from 4 to 10 per cent. The whole of the lime is lost, and two thirds of the total chlorine (in combination with calcium) contained in the acid used.[241]

[Footnote 241: Kingzett.]

When sufficient air has been blown into the oxidizer, the contents which consist of a solution of chloride of calcium, holding in suspension peroxide and protoxide of manganese and lime, are run into one of a range of settling tanks placed below the level of the oxidizer. These tanks are known as _mud settlers_. In these the manganese mud is left to deposit until about half its volume has become clear. It generally requires 3 or 4 hours to deposit. The clear part, which consists of chloride of calcium, being then decanted by means of a swivel-pipe, is usually thrown away. The mud remaining in the settlers, which contains in a cubic foot from 4 lbs. to 5 lbs. of peroxide of manganese, is now in a fit condition to be placed in the still, where it is to be exposed to the action of the hydrochloric acid. The stills, which are made of slabs of hard siliceous sandstone or of Yorkshire flagstones, and are usually in the shape of an octagonal prism, are about 8 feet square, and 10 feet in depth. Mr Kingzett says "the new Weldon stills are polygonal in shape, about 12 feet across, and 7 feet to 8 feet deep." Contrary to the course formerly followed, when native manganese was used in the Weldon process, the still is charged with hydrochloric acid first, and the manganese mud is run in upon the acid in a small, steady stream, the flow of which can be regulated by a stopcock. Steam being carefully admitted into the still at the same time, the mud dissolves very rapidly in the acid, and the chlorine is evolved in an even current, the force and flow of which is dependent upon and can be very accurately regulated by the admission of the mud.

The time occupied before the reaction between the acid and the manganese is completed varies in different works from two to six hours. At the end of this time the contents of the still are run off into the well placed below it, and are afterwards submitted to the various operations already described, which we have seen to accomplish the regeneration of the residue and effect its reconversion into peroxide of manganese. The process is a continuous one, and theoretically the original quantity of manganese should be capable of being used over and over again for an unlimited number of operations. In practice, however, there is always found to be a loss of a small per-centage of manganese, arising from some of the chloride of manganese being carried down by the sulphate of lime and the ferric and aluminic oxides in the settlers, and not being thoroughly recovered when the deposit is washed; for, though an exhaustive washing of the precipitated matters could be easily managed, the bulk of the wash waters would render the recovery of the chloride of manganese from them a non-paying affair. This loss of chloride varies according to the statements of different manufacturers from 2 to 10 per cent.

It is stated that not only is the chlorine yielded by Mr Weldon's process of very pure quality, and the bleaching powder manufactured from it very high of strength and excellence; but that over from 20 to 25 per cent. more bleach is obtained from a given quantity of hydrochloric acid, when artificial peroxide of manganese is used instead of the native. This advantage is chiefly owing to the artificial manganese (of the manganese mud) from its physical condition being much more accessible than the native form of manganese to the action of the hydrochloric acid, and from its dissolving in the acid so much more readily and thoroughly, and neutralising as much as from 95 to 99 per cent. of it, a much larger amount than the native ores are capable of neutralising.

Again, the bleaching powder produced by the above process stands not only very high in point of strength, but varies very little in the amount of chlorine it contains, as may be gathered from the following table, which shows the average strength for thirteen consecutive weeks of the bleaching powder made at six large and different manufactories:--

-------------------------------------------------
| FACTORY.
WEEK. |-----------------------------------------
| I. | II. | III. | IV. | V. | VI.
-------|------|------|------|------|------|------
1st | 36·9 | 37·8 | 36·7 | 36·3 | 36·6 | 36·6
2nd | 36·1 | 36·8 | 36·7 | 36·2 | 35·1 | 37·4
3rd | 36·5 | 38·0 | 36·6 | 36·1 | 37·2 | 37·9
4th | 35·9 | 37·1 | 35·9 | 36·2 | 36·8 | 37·1
5th | 35·8 | 36·9 | 36·0 | 36·3 | 36·5 | 37·8
6th | 36·0 | 37·0 | 36·2 | 35·9 | 36·5 | 37·2
7th | 36·5 | 36·0 | 36·3 | 36·6 | 35·8 | 36·8
8th | 36·3 | 36·8 | 36·3 | 36·3 | 35·0 | 37·1
9th | 36·4 | 36·3 | 36·8 | 35·7 | 35·2 | 37·0
10th | 36·5 | 36·7 | 36·3 | 36·0 | 36·2 | 37·6
11th | 36·8 | 36·8 | 36·2 | 35·9 | 36·0 | 37·2
12th | 36·8 | 35·9 | 35·6 | 35·6 | 36·1 | 37·2
13th | 36·7 | 35·2 | 35·9 | 36·1 | 36·9 | 37·5
-------------------------------------------------

Spite of the expensive plant required to work Mr Weldon's process, it is said to possess very decided advantages over the old methods as far as regards cost of production.

In connection with Mr Weldon's process may be mentioned Mr Valentin's modification of it, for which a provisional patent was taken out by this latter gentleman. Instead of adding more lime, after the neutralised still liquors have been precipitated by an equivalent of lime, as is done in the above process, Mr Valentin adds a solution of potassium ferricyanide, and air being blown in, the peroxidation of the manganese is effected much more quickly than in Mr Weldon's process. It was also calculated that, by Mr Valentin's method, bleaching powder could be produced at a cost of about ten shillings per ton less than when made by Mr Weldon's.

For the successful working of Mr Valentin's process it is necessary that the ferricyanide should be recovered, not only because of its cost, but also because its presence gives rise to the production of cyanogen compounds, which would enter the chamber with the chlorine. Hitherto no economical plan for the recovery of the salt has been devised, and consequently Mr Valentin's proposed modification of Mr Weldon's process has failed to be adopted.

_b._ A second process for obtaining chlorine, called "_the magnesia process_," has been devised by Mr Weldon. In the previous method, or "_lime process_," two thirds of the chlorine contained in the hydrochloric acid, as we have seen, is lost, passing away in the form of waste chloride of calcium.

In the "magnesia process" all the chlorine is utilised, the acid employed being made to yield the whole of its gas in the free state. The regeneration of the manganese peroxide being likewise accomplished, and the process being a continuous one, theoretically no loss of material should take place.

Beyond the employment of liquor pumps, no machinery is requisite for carrying out the operation, which, being very simple in its details, requires the employment of little skilled and, consequently, expensive labour. Further, the inventor claims for it the production of bleaching powder at a less cost per ton than by any other process. The "magnesia method" is worked as follows:--

The spent liquors of the still, consisting of chloride of manganese and free hydrochloric acid, are neutralised with magnesite, or, as it is sometimes called, Greek stone--a very pure native form of carbonate of magnesia. Sometimes the magnesite is calcined, and the magnesia thus obtained used instead.

The neutralisation may be effected either in the still itself, or in a well made of cast iron. The liquid is next pumped into the settlers, in which it deposits its ferric and aluminic oxides and sulphate of lime. The clear liquor containing the chlorides of manganese and magnesia is then run into an iron evaporating pan, where it is concentrated by boiling until it reaches a temperature of between 300° and 320° F. At this point the magnesium chloride begins to be decomposed by the water, and hydrochloric acid is given off. When it has reached the above degree of concentration, it is conveyed into a muffle furnace. This furnace is divided into two compartments, separated by an iron door, which can be opened or shut by means of a pulley placed outside. The desiccation of the mass which is accompanied with the evolution of a little chlorine and a large amount of hydrochloric acid, having been completed in one of the divisions of the furnace, it is broken up by constant stirring into thin cakes and raked into the second division, where it is gently heated with access of air; when the operation is complete the residue which left the first compartment as a mixture of manganese and magnesium chloride becomes converted into manganate of magnesia (MgMnO_{3}), its chlorine having been driven off partly in the free state and partly as hydrochloric acid. "As long as water is present in the furnace hydrochloric acid is evolved, and as the main evaporation takes place in the first division of the furnace, it is chiefly hydrochloric acid that is there generated. In the second division it is chiefly chlorine which is evolved, but it is, of course, mixed with some hydrochloric acid. It is, indeed, doubtful whether much manganese chloride is decomposed by the water so long as there remains any chloride of magnesium, as this body is far more readily decomposable."[242]

[Footnote 242: Kingzett.]

It is stated that all the manganese is not converted into peroxide in the furnace, but that a certain portion of it is left as protoxide; which, with the magnesia, constitutes the useless "bases." The completion of the process is known when portions of the cake drawn from time to time from the furnace cease to indicate any increase in the quantity of peroxide of manganese.

The finely-divided black powder--manganate of magnesium--thus obtained, after leaving the furnace and when sufficiently cold, is ready for the stills--where, in contact with hydrochloric acid, it is again employed in the generation of chlorine.

The chlorine leaves the furnace mixed with much hydrochloric acid, nitrogen, and air. The gaseous mixture is drawn by a chimney draught through the coke towers, as in the making of salt-cake. By this contrivance the hydrochloric acid is recovered, yielding a solution strong enough to react upon fresh manganese in the still. The diluted chlorine may be made to ascend leaden towers, where it comes in contact with a shower of milk of lime, which absorbs the gas and forms ordinary bleaching liquid, whilst sometimes it is employed in the production of potassium chlorate.

We have seen that the chlorine yielded by the "magnesia process" is partly in the concentrated, and partly in the dilute condition. The ratio of strong chlorine generated in the still to that of weak chlorine produced in the furnace may be anything between one to one, and one to about four, at pleasure.

"When working so as to obtain strong chlorine and weak chlorine in about equal proportions, the quantity of the liquor to be boiled down per ton of total bleaching powder made was about 105 cubic feet. As the proportion of the weak chlorine increased, the quantity of liquor to be boiled down diminished until, when the proportion of the weak chlorine to that of the strong became as four to one, the quantity of liquor to be boiled down per ton of total bleaching powder made was only about 40 cubic feet."[243]

[Footnote 243: 'Chemistry, Theoretical, Practical, and Analytical,'--Mackenzie & Co.]

11. (Deacon.) As we have already seen, Vogel proposed to obtain chlorine by the decomposition by heat of cupric chloride, and to reconvert the resulting cuprous chloride into the cupric salt by treatment with hydrochloric acid.

Chlorine may be produced by passing a mixture of gaseous hydrochloric acid and air over heated bricks or other porous substances, a reaction which Oxland unsuccessfully attempted to turn to account for the production of chlorine for manufacturing purposes. The cause of failure appears to have been the great heat necessary to effect the decomposition of the acid atmospheric oxygen.

In the late Mr Deacon's process both Vogel's and Oxland's methods are combined. He discovered that to be able to generate chlorine and water from gaseous hydrochloric acid and air, a very much lower temperature than that employed by Oxland was necessary, and he found that this diminished temperature could be attained, if the gas and air to be decomposed were passed over porous bricks saturated with a solution of sulphate of copper, and heated to a temperature of 700° to 750° F.

Beyond this point he found the heat ought not to be carried; for at 800° the cupric chloride formed begins to volatilise, and to condense in the cooler parts of the apparatus (presently to be described), thereby interfering with the draught through it, and delaying the working, since its removal becomes necessary. It was found that below 400° the reaction does not take place. Experience has demonstrated that the best temperature to effect this decomposition is 625° F.

The hydrochloric acid obtained either from a soda furnace or evolved from an aqueous solution is immediately mixed with a quantity of air containing an excess of oxygen over that required for liberating all the chlorine from the evolved hydrochloric acid, and passed through heated U-shaped tubes of cast-iron, from which the gaseous mixtures obtain the necessary temperature. The original plant was so contrived that the heated gases were conveyed from the U-shaped tubes into a series of nine towers made of iron or other suitable material. Entering by a pipe at the bottom of the first tower, and passing on to the second, the gases came into contact with a series of ordinary agricultural drain pipes of small bore arranged with vertical spaces, these pipes being saturated with a solution of sulphate of copper and sulphate of soda, it being subsequently found that this latter addition increased the efficacy of the copper sulphate, as well as its power to resist decomposition. From the first two towers of the series the mixed gases traversed the remaining ones, where they encountered small pieces of common brick, fire brick, or burnt clay also impregnated with the copper and soda sulphates, after reacting upon which they passed out of the apparatus, called the '_decomposer_,'

In the more recently made decomposers we believe the nine towers were abolished, and one chamber substituted for them, the drain-pipes being at the same time abandoned for pieces of brick and clay marbles.

A decomposer upon this latter principle is said to have been in use for several months at a factory in Berlin, and to have worked perfectly satisfactorily. After leaving the decomposer, the gaseous mixture, which now consists of chlorine, water, nitrogen, unconsumed oxygen, and undecomposed hydrochloric acid, after being cooled, is passed through water, by which means it is deprived of its hydrochloric acid.

It is next made to ascend a tower, where, meeting with a stream of sulphuric acid running over coke, it is deprived of its water. The chlorine (diluted with nitrogen and oxygen) is now ready for the lime chamber.

One great objection urged against the adoption of the above process, viz., that in consequence of the large volume of the evolved gases enormously large chambers for the preparation of the bleaching would be necessitated, seems to have been met by passing the gas through a series of chambers, in which the first contains nearly finished bleaching powder; the second, lime in a less saturated condition; and so on, until the last chamber contains merely slaked lime.

The following table, exhibiting the amount of chlorine contained in different batches of bleaching powder made by Deacon's process, is extracted from 'Chemistry, Theoretical, Practical, and Analytical,' published by Mackenzie:--

----------+-----------+----------+-----------
| Strength. | | Strength.
----------+-----------+----------+-----------
July 14 | 36·0 | July 22 | 34·3
" 15 | 34·8 | " " | 36·5
" " | 36·1 | " 24 | 36·8
" 17 | 36·4 | " " | 37·5
" " | 36·0 | " 25 | 36·1
" 18 | 37·2 | " " | 36·7
" " | 37·9 | " " | 36·8
" 19 | 37·2 | " 26 | 36·2
" " | 37·0 | " " | 36·9
" 20 | 37·9 | " 27 | 36·9
" " | 36·7 | " " | 35·5
" 21 | 36·0 | " 28 | 37·2
" " | 35·3 | " " | 37·0
" " | 37·7 | " " | 36·75
----------+-----------+----------+-----------

Writing on this process in his late work, 'The Alkali Trade,' Mr Kingzett says:--"The process bearing Mr Deacon's name was first brought before the public at the British Association Meeting in 1870.

"It excited at that time much attention, and indeed for some period it was doubtful whether it would not rival or even displace the Weldon process. Further experience, however, discovered difficulties in the practical working of this beautiful method, which exercise a deteriorating influence on its value, and lessen its applicability. Although several plants have been erected in connection with this mode of manufacturing chlorine, most of them have been since abandoned, and at the present time most of the chlorine is manufactured according to the process of Mr Weldon."

Dr Jurisch, in a communication to 'Dingler's Polytechnic Journal,' 1876, remarks that when Deacon's process was first taken up within a short time by more than twelve English and two German establishments, the view was generally entertained that the balls of clay steeped in solution of copper would ensure an uninterrupted production of chlorine gas for a year or two, if not longer. Before many months had elapsed complaints were heard of the action of the balls. He, therefore, undertook to determine what can be the cause of these balls declining so rapidly in their efficacy. His conclusion is, that the true cause of this speedy decrease in the decomposition is due to sulphuric acid, which passes through the interstices of the clay-balls mixed with the other gases. This injurious action, according to Hasenclever and Sartori, is probably to be explained by the following reaction:--The vapour of sulphuric acid in contact with sulphate of alumina at a dull red-heat, as is found in the balls, is resolved into sulphurous acid, watery vapour, and oxygen; the sulphurous acid thus formed is reoxidised at the expense of the free chlorine, is again decomposed, and thus keeps up a destructive circulation in the apparatus, which reduces or totally checks the chlorine.[244]

[Footnote 244: Extracted from the 'Chemical News.']

_Prices of Bleaching Powder_ (CLAPHAM).

In 1805 £120 0 0 per ton.
" 1810 84 0 0 "
" 1815 80 0 0 "
" 1820 47 0 0 "
" 1825 27 0 0 "
" 1830 23 0 0 "
" 1832 21 0 0 "
" 1835 23 0 0 "
" 1840 21 0 0 "
" 1846 18 0 0 "
" 1850 13 15 0 "
" 1855 10 15 0 "
" 1857 13 10 0 "
" 1860 11 0 0 "
" 1868 10 12 0 "

_Prop., Uses, &c._ Chlorine is a gas possessing a yellowish-green colour, and a pungent, suffocating odour. It is one of the heaviest substances that are gaseous at ordinary temperatures, being nearly 2-1/2 heavier than atmospheric air; sp. gr. 1·47. It is soluble to a considerable extent in water, that liquid at 60° Fahr. absorbing about twice its volume. It is non-inflammable, but its union with some of the elements is attended with the phenomena of combustion; thus, phosphorus, copper leaf, powdered antimony and arsenic, and several other substances thrown into chlorine immediately inflame. Under a pressure of 4 atmospheres it is condensed into a yellow, limpid liquid. Moist chlorine gas cooled to 32° Fahr. condenses into yellow crystals, containing 35-1/2 parts of chlorine and 90 parts of water. The most remarkable property of chlorine is its power of destroying almost all vegetable and animal colours, and the putrid odour of decomposing organic matter; hence its value as a bleaching agent, and as a disinfectant and fumigator. When first proposed as a bleaching agent by Berthollet, it was used much the same way as sulphur is now in bleaching woollen goods; afterwards a solution of the gas in water was employed, but the final improvement was Tennant's patent of combining the gas with lime to form "chloride of lime." With the bases chlorine forms an important series of compounds called chlorides.

_Tests._ Free chlorine is readily distinguished from other gases by its colour, suffocating odour, and bleaching properties. The aqueous solution dissolves gold leaf, and with nitrate of silver gives a white, curdy precipitate.

=CHLORINE STILLS.= The accompanying figure represents a section of one of the earlier forms of still used in the preparation of chlorine.

These stills were sometimes made of strong sheet lead, the lower part of which was enclosed in a jacket of cast iron, into which steam was forced, by which means the contents of the still were heated. The steam was injected from an ordinary boiler through the pipe H, and the materials, after the decomposition had been completed, were drawn off by the pipe G. The four openings, C, D, E, F, were secured by water lutes, capable of bearing a pressure greater than that required in the chamber where the saturation took place. In some cases the lower half of the still was made of cast iron, and fitted into a groove made in the upper part, the two sections being united by means of a strong cement. In the latter case the heating of the still was effected by a naked fire applied to the bottom. Into the orifice C the said materials employed were introduced, whilst the acid was poured through the opening F. The gas evolved passed off through the pipe E to the purifier and chamber, where it was absorbed by the lime, and converted into bleaching powder, and the shaft of the agitator passed up through D.

The use of the leaden stills survived for a longer time in France than in this country. In some parts of Germany large glass globes with long necks were employed, in which the chlorine was generated from a mixture of hydrochloric acid and manganese. But these were only applicable in cases where comparatively small quantities of bleaching powder were to be manufactured. When the chlorine is obtained from a mixture of manganese, common salt, and sulphuric acid, the apparatus, being required to withstand a greater heat, is made entirely of metal.

In fig. 2. _a a_ represents a shallow iron pan, fitted with the tube _b_, for the purpose of emptying the contents of the leaden cylinder _d d_. This iron vessel serves as the lower part of the cylinder _d d_, the top of which is provided with an opening for a funnel syphon tube, for the introduction of the acid, and another opening, _f_, for the manganese. The entire apparatus stands on a flue leading from the furnace.

The foregoing drawing represents a vessel for the manufacture of chlorine on a large scale, and is extensively used in Germany.

It consists of a cylindrical vessel of sandstone, the lower half of which, A, is carved out of a single block; the upper half, B, also of one piece, fits into the lower by means of a grooved joint, the two parts being united by means of a cement made of clay and boiled linseed oil. About six inches from the bottom the cylinder widens by 2 inches, and the rim thus formed carries a perforated bottom, C, upon which the manganese is deposited in large lumps. The tube D, likewise of stone, passes beneath the perforated bottom, and is at the other end joined to the steam-tube E. The steam must therefore, when introduced, enter the cylinder through the perforations of the false bottom. The top of the cylinder is closed by a lead cover, K, which is fastened down by means of iron clamps; this lid has an aperture, G, and the tubes E, F, H, pass through it; tube E serves, as already stated, for the introduction of the steam; tube F is for the delivery of chlorine; the bent tube, H, which ends in a funnel, for the introduction of the hydrochloric acid; and the opening G for throwing the lumps of manganese into the cylinder. The solution of manganese chloride, resulting from the action of the hydrochloric acid upon the manganese, is removed through I, which is kept closed by a wooden stopper whilst the reaction proceeds.

See also, under CHLORINE, the description of WELDON'S stills, and of DEACON'S apparatus.

=CHLORITE.= A salt in which the hydrogen of chlorous acid, HClO_{2}, is replaced by a metal or other basic radical. See CHLOROUS ACID.

=CHLOROCHROMIC ACID.= CrOCl. _Syn._ CHLOROCHROMIC ANHYDRIDE. _Prep._ Bichromate of potassium, 3 parts; common salt, 3-1/2 parts; are intimately mixed together, put into a glass retort, and oil of vitriol, 9 parts, added; heat is next applied and maintained as long as dense, red vapours are given off. The product in the receiver is a heavy, deep-red liquor, greatly resembling bromine in appearance. Water resolves it into hydrochloric and chromic anhydride.

=CHLORODYNE.= See PATENT MEDICINES.

=Chlorodyne= (Dr Browne's). Acid muriat. conc., 5 parts; ether, chloroform, tinct. cannab. Ind., tinct. capsici, of each 10 parts; morphia, prussic acid, of each 2 parts; oil of peppermint, 1 part; syrup, 50 parts; tinct. hyoscyami, tinct. aconiti, of each 3 parts.

=Chlorodyne, English.= A filtered mixture of 5 grammes tinct. aromat., 4 grammes tinct. opii simp., 1 gramme morph. mur., 10 grammes aq. amygd. amar., 80 grammes syrup of liquorice, 1 gramme extract of liquorice, 40 grammes 90 per cent. spirit of wine, 5 drops oil of peppermint, 10 drops ether, 30 drops chloroform.

=CHLOROFORM.= CHCl_{3}. _Syn._ TERCHLORIDE OF FORMYLE, FORMYL-CHLORIDE; CHLOROFORMYL, TRICHLOROMETHANE, CHLOROFORMUM, L. A remarkable fluid discovered by Liebig in 1830, and independently by Soubeiran in 1832, and carefully examined in 1834 by Dumas. In 1842 its action upon animals was investigated by Dr M. Glover, and in 1847 it was introduced to the medical profession as an anæsthetic agent by Dr Simpson of Edinburgh.