Determination of Water in Bleaching Powder JEROllIE GOLDENSON AND CH4RLES E. D.iNNER, Chemical Corps Technical C o m m a n d , A r m y Chemical Center, Md. .i distillation method is described for the determination of water in bleaching
powder and high-test calcium hypochlorites, involving heating the sample with o-dichlorobenzene to drive all the water into the graduated separator tube of a specially constructed one-piece apparatus.
T
ethane as the distillation liquid. Some modifications were made of the apparatus, such as use of a 500- or 1000-ml. boiling flask in place of the 2-liter flask used for the'larger samples of other materials, addition of a spherical joint for ease of changing the flasks, and replacement of the plain separator tube with a graduated tube. Results which agreed with those obtained by the federal specification method (3) were obtained providing the distillation was not continued for longer than 30 to 40 minutes. For longer periods of time, high results mere obtained which were thought to be due to reaction of the calcium hydroxide of the bleaching powder with the s-tetrachloroethane or hydrochloric acid liberated by the s-tetrachloroethane. At the suggestion of W, L. Drahenstatt of the Diamond Magnesium Company, o-dichlorobenzene was used as the distillation liquid in place of s-tetrachloroethane and results n-ere obtained which reached a maximum value in about 30 minutes and did not increase over a period of several hours.
HE Tvater content of bleaching powder, which is used for bleaching, disinfection, and decontamination, is an important factor in it,sstability ( 7 , 8 ) . Of lesser importance is its contribution to corrosion in containers and to caking in cold weather. This applies to bleaching powder made by the chamber or rotary processes and t o the high-test calcium hypochlorites. For these reasons, knowledge of the water content is particularly desifable to users of bleaching powder for procurement and specification purposes. A variety of methods have been tried for the determination of water in bleaching powder, such as by heating the powder quickly in a tube a t 200" to 250" and absorbing the liberated chlorine in potassium iodide solution ( 9 ) , by difference between 1007, and the tot,al percentages of calcium hypochlorite, calcium chloride, sodium chloride (if present), calcium hydroxide, calcium carbonate, calcium sulfate, and insolubles in acid, and by passing dry air over the bleaching polvder, then over phosphorus pentoside, and obtaining miter by increase in weight of the phosphorus pent,oxide. In general, such methods are considered unsatisfactory because t,hey are either lengthy or inaccurate. Oven-drying methods cannot be used because the calcium hydroxide in the bleaching pon-der combines with carbon dioxide in the atmosphere and the calcium hypochlorite of the povider decomposes on heating. The method of direct deterniination of Ivater content bl- distillation (3, 4,1 1 ) has been most widely used. Somiya ( I I ) modified the apparatus devised by Dean and Stark ( 2 ) for water determination by distillation and used solvents heavier than water, such as carbon tetrachloride and t,etrachloroethylene. The federal specification method (3) for water in bleaching material involves distillation of the water from the bleaching powder with odichlorobenzene and collection of the distillate in a 100-ml. centrifuge t,ube graduated at t,he bottom for a t least 1ml. in 0.2-mi. divisions and containing petroleum et,her. The Pennsylvania Salt 1Ianufacturing Company uses a modification of the federal specification method, in which some minor changes are made in the distillation apparatus and a 100-ml. Goet,z cent,rifuge t.ube having a stem with rhe first milliliter graduated in 0.05-ml. divisions is used as a receiver. The excellent method of Suter (12) for determinat,ion of water in caustic soda and ot8heralkaline materials, involving disrillation follon-ed by a Fischer moisture titration of the distillates, cannot be applied as bleaching pori-der releases volatile oxidants on heating. In the distillation methods of Lundin (6) and Thielepape (IS), the vapor enters the top of the condenser and the separatgd water is continuouslr washed down into the trap by the condensing solvent. Lundin used a mixture of solvents containing tetrachloroethane, which was much higher in density and boiling point than TTater. A similar method developed by Greene (6) for the determination of moisture in tetrachloroethane, hexachloroethane, and chlorinated paraffin has been adapted to the determination of water in bleaching poJvder for Chemical Corps experimental xvork and procurement specifications. This method and apparatus as modified for bleaching p o d e r have some advantages over the methods previously mentioned in that the condenser and receiver of the apparatus ale in one unit, only one solvent is used, and inflammable solvents, such as petroleum ether, are not required, and after the distillation has been started no further attention of the operator is needed until the final reading is made. S o reference to this method as applied to bleaching powder is given in the literature, and it might be useful to analysts concerned with bleaching powder.
APPARATUS
The apparatus is constructed as shown in Figure 1. The dimensions given should be carefully duplicated to obtain satisfactory results.
n
6MM. TUBING
B A L L JOINT (CLAMPED)
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