Standard Bleaching Powder

The advantage of calcium hypochlorite, compared to standard bleaching powder, is a higher content of active chlorine. Moreover, it forms clear solutions in water and is much more stable particularly at higher temperatures. After 5 years storage in tropical countries, chlorine content will not drop below 55 per cent. Another advantage of the calcium hypochlorite is that it is less hygroscopic due to a lower content of calcium chloride. 

Procedure (iodometric method). Weigh out accurately about 5.0 g of the bleaching powder into a clean glass mortar. Add a little water, and rub the mixture to a smooth paste. Add a little more water, triturate with the pestle, allow the mixture to settle, and pour off the milky liquid into a 500 mL graduated flask. Grind the residue with a little more water, and repeat the operation until the whole of the sample has been transferred to the flask either in solution or in a state of very fine suspension, and the mortar washed quite clean. The flask is then filled to the mark with distilled water, well shaken, and 50.0 mL of the turbid liquid immediately withdrawn with a pipette. This is transferred to a 250 mL conical flask, 25 mL of water added, followed by 2 g of iodate-free potassium iodide (or 20 mL of a 10 per cent solution) and 10 mL of glacial acetic acid. Titrate the liberated iodine with standard 0.1M sodium thiosulphate. 

Iodometry is an indirect procedure based on the aforesaid reversible reaction whereby the assay of oxidizing agents, for instance available chlorine in bleaching powder, cupric and ferric salts may be carried out by reducing them with an excess potassium iodide thereby liberating an equivalent quantity of iodine which can be estimated using a standard solution of thiosulphate. 

Example. —20 grms. of bleaching powder were made up with water to a litre, and 25 c.e. were titrated with fV-standard sodium arsenite soln., i.e,. a soln. of such a concentration that 1 c.c. corresponded with 0 "00355 grm. of chlorine. After the addition of 46 c.c. of tbe standard soln., a drop of the liquid being titrated gives no coloration with starch and potassium iodide. Here 46 x0"00355=0"163 grm. of available chlorine was contained in 25 c.c. of the given soln. or 6"5 grms. per litre of the soln., i.e. in 20 grms. of the sample. Hence the sample contained 32 "5 per cent, of available chlorine. 

The commercial solution of sodium hypochlorite contains 14-15% available chlorine, compared to 35-36% in bleaching powder. The concentration of hypochlorite in the bleaching bath generally varies from 1 to 3 g/1 available chlorine. The optimum bleaching conditions, however, depend on the degree of discolouration of the cloth and thus the temperature and time of reaction should be adjusted according to the requirement. The concentration of hypochlorite solution is normally estimated by means of standard thiosulphate or arsenite titration. 

Available chlorine in a sample of bleaching powder is estimated volumetrically. A known mass of bleaching powder as a suspension in water is treated with excess of potassium iodide solution. The solution is then acidified with a strong solution of acetic acid. Iodine is liberated which is titrated against standard sodium thiosulphate solution. 

Most of the CA produced commercially is chlorinated to produce SDCC, SDCC-H, PDCC, TCCA, and the double salt TCCA4PDCC. These have become standard ingredients in formulations for scouring powders, household bleaches, institutional and industrial cleansers, automatic dishwasher compounds, and general sanitizers, and most importantly, in swimming pool and spa/hot tub disinfection. The choice of chloroisocyanurate for any particular... 

Commercial lecithin is produced by water degumming (precipitation from oil with ion-exchange treated water), separation by stacked disk centrifuge, and vacuum drying to less than 1 percent moisture content. Crude lecithins contain 70-72 percent acetone insolubles (AI) and are standardized to 62-64 percent and an acid value of 30 by addition of oil and fatty acids before sale. Crude lecithins may be treated with acetone to obtain free-flowing powders with 95-98 percent AI. Lecithin can be additionally purified, bleached, fractionated, hydrogenated, hydrox-ylated, acetylated, sulfonated, and halo-genated.104 One domestic company makes 13 kinds of lecithin for food uses alone. 

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