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the, calcium were not precipitated tiis way. s,. ale - wo%d be formed. By adding sodic, exametai-;l )s- phate to a boiler feed. orthophosphate is obtained in thg boiler but deposition does not usually occur in the feed lines. Sequestering Power The property on which much of the commercial importance of sodium hexametaphosphate depends is that known as sQquesterinq power. This is the ability to_lake metal ions into a soluble complex In vvnrrh ingy no Inri snow (herr cn.aracteris _(, rcaclions. thus. calcium ano magnesium in naro witei can be so complexed by SHMP that they are not precipitated by soap, and the water is effectively softened. The sequestering of copper, iron and zinc by sodium hexametaphosphate has also found industrial appli- cations. This property is of greatest importance In de'clgent operations because hardness in water can greatly reduce the effectiveness of soap. synthetic detergents and alkalis. There are further advantages in textile and laundry processing. in that deposits formed during earlier treatments may be removed. in processesusing soap, each ppm hardness requires about 6 ppm sodium hexametaphosphate (6g per, ml. 0-1 oz per 100 gallons). These figures are approximately true for low titre soaps in cold and high titre soaps in hot liquors. About 1w0 -thirds of the above concen- tration of SHMP Suffices with synthetic detergents which are also adversely affected by hard water. Threshold Effect The presence of very small amounts of sodium hexa- metaphosphate, of the order of a fe-N parts per million, will delay considerably the precipitation of calcite, the form in which calcium carbonate is usually deposited when vvater containing temporary hardness is rendered unstable. This phenomenon Is believed to be due to the disturbance of the crystal growth by adsorption of the complex phosphate on the calcium layers in the surface of the calcite nuclei. Deflocculation Sodium hexametaphosphate. In common with other soluble compiex phosphates. such as sodium tripc,ly- ph.osphate. car) deflocculate some Insoluble inorganic solids and Is therefore used to disperse substances such as clays ;Ind mineral pigments in water. Fir example. the adclojon of very small quantities of SHMP to stiff pastes of Ilthopune will reduce them to mobile slurries. The concem ration which is most effective for this purpose normally lies III the range 01% to 0 5% SHMP on the eveight of the solid, but the optimum amount required in any particular system must be deter- mined experimentally. Applications of this property Include deflocculation of clay in slip -casting, and dispersion of pigments in paper coaling an; emulsion paints. Coagulation of Proteins One of the properties of complex phosphates known for a long time is the reaction with albumen to give a precipitate in weakly acidic solutions. It has been used in qualitative analysis as a means of distinguishing cornpiex phosphate from the other- phosphates. The reaction is not limited to albumen but occurs with other proteins. The addition compounds which are formed are soluble in neutral salt solutions. The main ust of this reaction is in the tanning or pre- ', : tanning of leather, but sodium hexametaphosphate has' also been used in analysis for the deproteinization of ei-turions in the determination of vitamin C. Apptic .%.-� is Boiler Water Treatme.. For many years, phosphates have been accepted as the most effective reagents for the prevention of calcium scale in high-pressure boilers, and phosphate con- ditioning is now used in all types of boilers over the whole range of working pressures. Sodium hexameta- phosphate has proved a convenient source of phos. , phate, and it has two important advantages over the orthophosphates: {1) It gives a lower boiler alkalinity than either di- or =` trisodium orthophosphate. (2) By intermittent feeding, it is possible in most' > plants to add SHMP through the fce.d tines without the formation of deposits. This Is generally impossible with an orlhophosph, le. Threshold Treatment In this process. water is treated with low (Ihroshold) concentrations of sodium hexarnetcphosphate, the amount used being normally less tl,5n five ppls pot million (50 per m3, or 5 Ib per 100,000 gallons) of wzler, There aro four dlffc-tnt types of ppplrcatron of $HMD in these minute concentrations: ` (1) The prevontion of scale formntlon In but v*clQr Supply systems, condenters and ofhv plant In which waters with a high ttn)porpry hardness We raised In temperature Usually 2-b ppm sodlurn hcz5r,:El:pr10:tpttG'tQ it for Ihig purpose. (2) The stabilization of herd wwrt to ptevGnt the formalion Of calcium carbonilo . scale when alkalis are added. This is useful in the porlial softening of water supplies by the nddltion of lime where after-precipilalion is a problom,' and in the treatment of waters with ammonia which is often added before chlorination. This applica- tion is satisfactory with very low concentrations of sodium hexametaphosphate, sometimes as little as0.25 ppm. to deal with after -precipitation. (3) The prevention of corrosion of iron and steel water -mains by soft waters of the moorland type. This can be used to control tuberculation both in supply mains and in hot water systems. The amount of sodium hexametaphosphate necessary varies with the rate of flow of the water and the temperature. but -should always be such as to maintain a reserve of 2-3 ppm of SHMP in the water. (4) The prevention of the separation of iron com- pounds from well waters containing ferrous bicarbonate in solution. The concentration of sodium hexametaphosphate should be about twice the total iron concentration in the water and not less than 2 ppm. Detergent Operations The ability to sequester calcium ions enables sodium hexarnetaphosphate to dissolve or prevent the formation of insoluble soaps and to prevent the interference of hardness in water with the efficiency of synthetic detergents. SHMP has. therefore. very wide application in detergent operations. some examples of which are as follows: Texti✓es. Sodium hexametaphosphate is widely used in the scouring of woollen and worsted piece goods: it is normally added to a special bath during washing off. Similar uses are in the keir-boiling of cotton. the de - gumming of silk and in some dyeing processes. Laundries. The greying of laundry .work is often due to the deposition of insoluble soaps during the rinse. This can be prevented by adding sodium hexametaphosphate in the first hot rinse of any of the normal washing