LEVELING STOPCOCK 



DELIVERS _STOP 



SILVER CHLORIDE 

 WASTE BOTTLE 



Figure 13-2. Knudspn burette assembly. 



The background behind the burette should 

 be painted flat white to aid in reading the 

 burette without glare and give proper light for 

 color interpretation of the titration end point. 

 A fluorescent titration lamp should be rigged 

 behind the magnetic stirrer at a height to 

 provide proper light to the sample. 



It is advantageous to have on hand a simple 

 glass stirring rod about 6 inches long, blunted 

 at one end and bent at the other at about a 40° 

 angle for the last half inch. The ends of the rod 

 should be fire-polished. The stirring rod is 

 used for transferring half drops of solution 

 from the delivery tip of the burette to the 

 sample in the beaker during the final stages of 

 the titration run. 



If the silver nitrate solution bottle can be 

 placed in a sea rack on a shelf that is high 

 enough to permit gravity flow to fill the burette, 

 then the pressure bulb shown in figure 13-2 

 will not be needed. Due to low overhead on 

 most ships, this usually is not possible and use 

 of the pressure bulb will speed the refilling 

 of the burette. 



Silver nitrate is sensitive to light, and the 

 solution will decompose if exposed to light for 

 long periods. A satisfactory container for the 

 solution is a 5-gallon, wide-mouth bottle or 

 carboy. The bottle must be painted with 

 several coats of black paint to make it light- 



proof, except for a small (half-inch) vertical 

 slit through which the solution may be seen. 

 The edge of the slit may be graduated by 

 liters with white paint to show the amount of 

 solution remaining in the bottle. Clean the 

 inside thoroughly with soap and water. Rinse 

 with tap water. Give a final rinsing with 

 distilled water and dry before using. 



A waste receptacle for the titrated samples is 

 necessary. The best type is a wide-mouth, 

 5-gallon bottle or carboy. This bottle should 

 be secured on the deck beside the titration 

 table. The precipitate of silver chloride which 

 is collected in the bottle is removed and dried 

 after the bottle gets about two-thirds full. 

 The method for drying is given in section 13-34. 

 From time to time, the excess water can be de- 

 canted from the bottle. If the water becomes 

 red in the bottle add a little sea water to it. 

 It is recommended that when running titra- 

 tions keep a funnel in the mouth of the bottle. 

 This will make it easier to pour waste into the 

 bottle and will prevent the magnet used in 

 stirring from being dumped accidentally into 

 the bottle. 



13-25 Preparing the Indicator Solution. — 

 Potassium chromate (K2Cr04) is used as the 

 indicator in determining the end point of the 

 titration. This solution is made by dissolving 

 8 grams of chemically pure potassium chromate 

 in 100 ml. of distilled water. This solution is 

 kept in a 125-ml. dropping bottle that has 

 been cleaned with acid-dichromate cleaning 

 solution, rinsed with distilled water, and dried. 



13-26 Preparing the Silver Nitrate Solu- 

 tion. — The silver nitrate solution is made by 

 dissolving 37.11 grams of silver nitrate in 1 

 liter of distilled water. It has been fotmd that 

 the best results are obtained by making up 

 larger batches of solution than 1-liter amounts. 

 It is easier to make a correct solution when 

 making a 10-liter batch than a 1-liter batch 

 because the smaller the amount the greater the 

 chance of error. One drop spilled would make 

 a difference to 1 liter but only one-tenth as 

 much difi'erence to 10 liters. 



As a triple beam balance can be used only 

 ashore or when the ship is in port, it is recom- 

 mended that the silver nitrate needed for a 

 cruise be weighed out ashore and sealed in small 

 clean glass jars. For 10-liter batches of solu- 

 tion, weigh out 371.1 grams per jar. 



To mix a 10-liter batch, first open a silver 

 nitrate jar and carefully pour all the crystals 

 into a clean 800- or 1,000-ml. beaker. Add dis- 

 tilled water to the beaker by pouring it first 

 into the jar and then into the beaker. Repeat 

 this until the beaker is about three-fourths 



122 



H. O. 607 



