QX^\NTITATIVE SEPARATION OF LITHIUM. 19 



very slight precipitate is formed at this point, the filtrate from it 

 is evaporated, the ammonium salts driven oft", the residue taken 

 up in vater, filtered, and tested again with ammonium carbonate 

 and oxalate. This is repeatetl as man}^ times as necessary until 

 no further precipitate is obtained. The filtrate is evaporated to 

 dryness in a jjlatinum dish suitable for weighing, taken up with a 

 little hydrochloric acid and water, and again evaporated. The dish 

 is gentl}' heated to drive off ammonium salts, and the mixed chlorids 

 are heated nearly to fusion. When cool, the dish and contents are 

 weighed and heated to constant weight with ignition barely to 

 redness, avoiding prolonged heating. 



While sodium chlorid will stand a high temperature for a long time, 

 the potassium chlorid is slightly volatile, and lithium chlorid is con- 

 siderably more so and in addition is liable to decomposition. Pure 

 lithium chlorid in quantity is difficult to weigh by ordinary methods. 

 On account of the heat necessary' to drive off the water, there is 

 danger of a slight loss from volatilization or decomposition of some 

 of the salt. As usually found in waters, however, the amount of 

 lithium is so small in proportion to the sodium that the chance of 

 loss is much lessened. After bringmg to constant weight, the mixed 

 chlorids are dissolved in a few cubic centimeters of water and fil- 

 tered through a small filter into a 100-cc Erlenmeyer flask. The 

 filter paper mth the small amount of insoluble matter is burned in 

 the dish and the weight of the dish and ash subtracted from the 

 previous weight gives the weight of sodium, potassium, and lithium 

 chlorids. 



The solution of mixed chlorids in the flask is boiled down (after 

 the addition of a piece of platinum foil to reduce bumping) until the 

 salts are about to crystallize out. Amyl alcohol is then added up 

 to a volume of about 40 cc, a cork with thermometer and delivery 

 tube inserted, the delivery tube joined to a condenser and receiver, 

 and the contents of the flask boiled until the thermometer registers 

 the boiling point of the amyl alcohol, 130° to 132° C. The flask is 

 cooled, one or two drops of dilute hydrochloric acid added, and the 

 distillation contmued until the temperature of the vapor again 

 reaches its highest point. The flask is then slightly cooled and 

 the contents filtered through a small Gooch crucible with asbestos 

 mat into a 50-cc graduated cylinder. The volume (usually from 10 

 to 25 cc, according to the amount of Utliium expected) is noted, 

 and the flask and crucible are washed two or three times with a 

 few cubic centimeters of anhydrous amyl alcohol from which the 

 water has been boiled out just before separating the lithium. The 

 amyl alcohol solution containing the lithium chlorid with some 

 sodium and potassium chlorids is evaporated to dryness in a plati- 

 num dish. To convert the chlorids into sulphates, the residue is 



