XIII. A, 1 Heise and Behrman: Water Analysis in Field 7 



sodium carbonate for acidity; silver nitrate for chlorides; and 

 potassium palmitate for total hardness. 



KaoHn is used as the filter and binding material for the sodium 

 carbonate and silver nitrate pellets, while glucose is employed 

 for those of sodium acid sulphate and potassium palmitate. 

 Glucose is superior to kaolin, as it is completely soluble and 

 consequently does not obscure the end point. It cannot, how- 

 ever, be used in the first two cases, because unstable pellets 

 result. Water is used in all cases in making up the pill mass. 

 The reagent is dissolved in water and carefully stirred into the 

 binding material. The mass is kneaded in a mortar, more water 

 being added if necessary, until it is homogeneous and of the 

 desired consistency. 



The tablets are made in a tablet mold. We use a hard rubber 

 mold (No. 10, Whitall Tatum Company, for making 50 one- 

 grain tablets at a time). The molded pellets are dusted with 

 powdered talc, dried in the air and then in a desiccator over 

 calcium chloride, after which they are packed in glass tubes, 

 about 15 centimeters in length and holding about forty pellets 

 each. The tubes are sealed with paraffin, and those containing 

 pellets of silver nitrate are covered with heavy black paper. 

 Needless to say, the silver nitrate pellets are made in a dark room. 



The silver nitrate and sodium carbonate pellets retain their 

 strength almost indefinitely without change. Those of sodium 

 acid sulphate lose strength very slowly and should be restandard- 

 ized every month. The potassium palmitate pellets lose strength 

 rather rapidly and should be restandardized weekly. 



Alkalinity. — Pellets are molded from a pill mass containing 

 6.5 grams of crystallized sodium bisulphate and 150 grams of 

 glucose, the proportions that will yield a pill of very nearly the 

 desired strength (one pellet equivalent to 1 milligram calcium 

 carbonate, CaCOg). The pellets are standardized by crushing 

 five of them in a mortar with a little distilled water and adding 

 a drop of butter yellow indicator solution (0.2 gram butter yellow 

 in 100 cubic centimeters of alcohol). Tenth-normal sodium 

 hydroxide or sodium carbonate is added till the end point is 

 reached. From this titration the reacting value of the pellets 

 may be readily calculated. 



The field determination of alkalinity is analogous to the stand- 

 ardization of the pellets. The 100 cubic centimeter cylinder 

 is filled to the mark with the water under examination. Two 

 or three of the pellets are crushed in the mortar with a little 

 of the water, and a drop of the indicator is added, followed by 

 more water from the cylinder till the end point is reached. 



