857 



CHLORIMETRY. 



CHLORINE. 



necessary to convert a given weight of protosalt of iron into persalt of 

 iron, it is only necessary to add our solution of bleaching powder of 

 unknown strength to that given weight of protosalt of iron, till it 

 ceases to yield a blue precipitate with red prussiate of potash, when 

 the amount of chlorine in the quantity of bleaching solution we have 

 used is at once indicated ; and if we have made that solution with a 

 weighed quantity of bleaching-powder, the strength, and therefore the 

 commercial value of that powder is, by a very simple calculation, 

 readily ascertained. The following are the details of this process : 



78'1 grains of pure, dry, recently-prepared protosulphate of iron 

 (green vitriol) are dissolved in about two ounces of water, and a little 

 sulphuric or hydrochloric acid added ; to convert this into persulphate 

 of iron, ten grains of chlorine are necessary. Fifty grains of the 

 sample of bleaching-powder are rubbed in a mortar with a little water, 

 and the mixture introduced into such a burette as under the article 

 ALKALIMETRY is designated an alkalimeter ; the mortar is washed with 

 a little more water, and the liquid added to that already in the burette, 

 which is then filled up to o, and the orifices being closed by the finger 

 and thumb, thorough mixture is promoted by agitation ; each division 

 marked on the burette will now contain half a grain of bleaching- 

 powder. To the solution of protosulphate of iron, placed for conve- 

 nience, and to ensure accuracy, in a stoppered bottle of about six 

 ounces capacity, is added the bleaching solution from the burette, till, 

 after agitation, a drop placed on a white plate gives no blue precipitate, 

 but only a alight green colouration, when a drop of solution of red 

 prussiate of potash is added to it. The number of burette divisions of 

 bleaching solution used will obviously contain ten grains of chlorine ; 

 and, as each division contains half a grain of bleaching-powder, the 

 whole number used in the experiment, divided by two, indicates the 

 number of grains of chloride of lime that contain ten grains of chlorine. 

 A short calculation gives the amount of available chlorine in 100 grains 

 of the sample of chloride of lime subjected to analysis. Let m repre- 

 sent the number of measures used, then 



: 10 : : 100 : x 

 2 



x will be the percentage of available chlorine. 



The reaction that takes place will at once be seen by a glance at the 

 following equation : 



2(FeO,SO 3 ) + 2(110,80.,) + CaO, Cl = Fe,O 3 , 3SO 3 + HC1 + CaO, SO 3 + HO 



rrotosulphate Sulphuric Chloride Persulphate Hydro- Sulphate Water. 

 of iron. acid. of lime. of iron. chloric of lime. 



acid. 



Two other chlorimetrical processes have been proposed, both similar 

 in principle, but not generally superior, to the one just described. In 

 one, arsenious acid (AsO,) is used in the place of the protosulphate of 

 iron ; the chlorine converts it into arsenic acid (As0 5 ). In the other, 

 yellow prussiate of potash (ferrocyanide of potassium) is the agent 

 employed to absorb the chlorine ; from every two equivalents of it 

 (2K.,Cfy = K,Cfy 2 ), one equivalent of chlorine abstracts one equivalent 

 of potassium, forming chloride of potassium, leaving an equivalent of 

 the red prussiate of potash (ferrocyanide of potassium = K 3 Cfy 2 ). The 

 arsenious acid process is known to be complete when a few drops of 

 indigo solution, with which the mixture is tinted, are decolorised ; the 

 prussiate'process is known to be complete when the mixture no longer 

 gives a blue precipitate with a persalt of iron. 



Chlorimetry is almost an hourly operation with the calico bleachers, in- 

 asmuch as the dilute solution of chloride of lime contained in their steep- 

 ing vessels is, of course, much weakened by the immersion of a large 

 quantity of unbleached goods ; and the strength of the weakened solution 

 requires to be known, in order that the proper quantity of the strong stock 

 solution of chloride of lime may be added to restore the bath to its original 

 strength. This is the more important on account of the limited range 

 of strength of the steeping liquor, within which the cotton is properly 

 bleached : if too strong, the goods are injured; if too weak, the fabric 

 still remains brown. It is, therefore, very necessary that the calico- 

 bleachers should possess a chlorimetric process that can be quickly, as 

 well as accurately performed ; and for this reason they usually adopt 

 the method known as , 



Ontrn's proctu. This test is based on the same principles as Daltou s 

 test namely, that chlorine converts a protosalt of iron into a persalt, and 

 that a (riven quantity of the protosalt always requires the same amount 

 of chlorine for its conversion ; but the colour of a constant volume of 

 the bleaching solution containing excess of protosalt of iron is made 

 use of to determine the amount of persalt of iron in it ; the intensity 

 of thia colour is obviously in direct proportion to the quantity of avail- 

 able chlorine in the volume of bleaching solution used. The following 

 are the details of this operation : 



The protoualt of iron used is the protochlonde, and is made by 

 diverting excess of cart-iron turnings in hydrochloric acid, diluted with 

 about half its bulk of water, at the temperature of boiling water, till all 

 action has ceased. When cold, this solution is diluted till it has a 

 Hnccific gravity of 1-200, equal to 40 degrees on the scale of Twaddell's 

 hydrometer, the instrument usually adopted by manufacturers for 

 t iking specific gravities. This liquid, mixed with acetic acid of sp. gr. 

 1-0*8 forms the proof solution. Diluted with water, it is colourless, 



but the addition of chlorine gives rise to the formation of peracetate of 

 iron, which has a peculiarly intense red colour. A quantity of this 

 proof solution, measuring about a quarter of an ounce, is put into a 

 clear white glass moulded phial of two ounces capacity, which is then 

 filled up with a solution of chloride of lime that has a specific gravity 

 indicated by one-twelfth of a degree on Twaddell's hydrometric scale. 

 This operation is repeated with eleven other phials of exactly equal 

 diameter, the bleaching solution with which they are filled up being 

 each time carefully made one-twelfth of a degree stronger, so that the 

 last phial will be filled up with bleaching-solution of one degree in 

 strength (= sp. gr. 1'OOS). They should all be well corked and placed 

 side by side in a frame, leaving a little space between every other one. 

 The steeping solution used by calico-bleachers usually ranges from 

 one-half to one degree Twaddell, and when weakened by the immer- 

 sion of a parcel of goods, its strength is at once ascertained by filling 

 up with it a phial containing proof solution similar to those just 

 described, and placing it by the side of the standard phial nearest to 

 it in colour ; the strength of the solution in that phial being known, 

 the strength of the bleaching-liquid tested is at once indicated. If 

 now the quantity of steeping solution used in one operation is known, 

 and if a concentrated solution of chloride of lime is kept in stock, 

 made always of the same strength, a table may be constructed which 

 shall show at a glance the amount of stock solution required to be 

 added to the weakened steeping-liquor, to make it stand at the desired 

 strength. These conditions always exist in bleaching-works. The 

 steeping vessels described in Mr. Crum's paper required 1440 gallons 

 of liquid to fill them up to a mark indicating the proper height for 

 receiving goods, a quantity more conveniently expressed by 288 

 measures a measure containing five gallons, the quantity most easily 

 carried at a time. The stock solution of bleaching-powder was always 

 made of a density indicated by six degrees on the scale of Twaddell's 

 hydrometer. The following table was then constructed : 



To stand -i". 

 requires 32 measures. 



28 

 24 

 20 

 16 

 12 



To stand -f.,\ 



requires 1G measures. 



1 12 



2 8 



3 4 



To stand T \'. 



requires 24 measures. 



1 20 



2 16 



3 12 



4 8 



5 4 



To stand ~^. 

 requires 12 measures. 



This table shows, for example, that if the steeping liquor is required 

 to be of a strength indicated by J, of a degree Twaddell, the 288 

 measures must contain 32 measures of the stock-bleaching solution ; 

 if that steeping liquor is then weakened, and an experiment shows it 

 to be of a strength equal to three degrees Twaddell, then to 268 

 measures of it, 20 measures of stock-bleaching solution will be required 

 to be added to form 288 measures of steeping liquor of the original 

 strength, ^. In fact, every twelfth of a degree requires four measures 

 of stock solution in the 288 measures of steeping liquid. 



CHLORINDOPTIC ACID, Trichlwophenylic Acid, Chlorophcnisic 

 Acid (C, 2 H 3 Clj0 2 ),one of the chlorine substitution products of carbolic 

 acid. [CARBOLIC ACID.] 



CHLORINE (Cl), an elementary gaseous body discovered by Scheele 

 in 1774 [SCHEELE, Bioa. Div.], while examining an ore of manganese. 

 He'gave it the name of depldoyislicatcd marine acid. By the French 

 chemists, in accordance with the views of Berthollet, it was called 

 oxygenised muriatic acid, which was shortened by the English chemists 

 to oxymuriatic acid ; these latter terms meant that it was a compound 

 of muriatic acid, a supposed elementary or at any rate an undeeomposed 

 body, and oxygen. Gay-Lussac and Thenard in 1809 published some 

 experiments from which they inferred that oxymuriatic acid might be 

 a simple substance, but they notwithstanding adhered for a consider- 

 able period to the opinion of its being a compound. About the same 

 time Sir H. Davy commenced his examination of thS same body, and 

 from his numerous researches he concluded that it ought to be regarded 

 as an undeeomposed body ; and on account of its colour, he gave this 

 gas the name of chlorine, from xAwpifs, green. Chlorine was first 

 obtained by Scheele, by treating the binoxide of manganese with 

 hydrochloric acid. During the mutual operation of these compound 

 bodies, the oxygen of the binoxide combines with the hydrogen of the 

 acid, and water is formed ; the metal of the oxide remains combined 

 with a portion of the chlorine, while the excess which the metal does 

 not unite with is given out in the gaseous state, thus : 



MnOj + 2HC1 = MnCl + 2HO + Cl 



Binoxide Hydrochloric Chloride of Water. Chloiine. 

 of magnnese. acid. manganese. 



At the present day the above process is largely adopted, on account of 

 the cheapness of hydrochloric acid, which is obtained as a bye-product 



