46 METHODS OF ANALYSIS [Chap. 



hoi (130°C.) to remove the water. Cool slightly and add a drop of hydrochloric acid 

 to convert small amounts of lithium hydroxid to lithium chlorid. Connect with the 

 condenser and repeat the boiling until the temperature reaches the boiling point of 

 amyl alcohol to again drive off the water. The content of the flask at this time is 

 usually 15-20 cc. Filter through a small paper or a Gooch crucible into a graduated 

 cylinder and note the exact quantity of the filtrate, which determines the subsequent 

 correction. Wash the precipitate with small quantities of amyl alcohol. Evapo- 

 rate the filtrates and washings in a small platinum dish to dryness on the steam bath, 

 dissolve the residue in water, and add a few drops of sulphuric acid. Evaporate on 

 a steam bath and expel the excess of sulphuric acid by heating gently over a Bunsen 

 burner until the carbonaceous matter is completely burned off, repeating the addi- 

 tion of a few drops of sulphuric acid if necessary. Cool and weigh the dish and 

 contents, (x). Dissolve in a small quantity of hot water, filter through a small 

 filter, wash and return filter to dish; ignite and weigh, (y). The difference between 

 (x) and iy) is the weight of impure lithium sulphate. 



The purity of the lithium sulphate should be tested by adding small amounts of 

 ammonium phosphate solution and ammonium hydroxid, which will precipitate any 

 magnesium previously present in the lithium sulphate. Any precipitate appearing 

 after standing overnight should be collected on a small filter, ignited, weighed as 

 magnesium pyrophosphate, calculated to sulphate and subtracted from the weight 

 of the impure lithium sulphate. 



From this weight subtract 0.00113 gram of sodium and potassium sulphates for every 

 10 cc. of amyl alcohol filtrates, exclusive of the amyl alcohol used in washing the 

 residue, on account of the solubility of sodium and potassium chlorids in amyl alco- 

 hol. Calculate to lithium from the corrected weight of lithium sulphate. 



Dissolve the mixed chlorids from the flask and filter with hot water, evaporate 

 to dryness, ignite gently to remove amyl alcohol, filter, and thoroughly wash; con- 

 centrate the filtrates and washings to 25-50 cc. Transfer to a porcelain dish, add 

 sufficient platinic chlorid solution [I, 40 (b)] to convert sodium and potassium to 

 their respective double chlorids and evaporate to dryness. Treat the residue 

 with 80% alcohol, filter, and wash until the excess of platinic chlorid and sodium 

 platinic chlorid has been removed. Dry the filter and precipitate, dissolve the 

 residue in hot water, and transfer to a weighed platinum dish. Evaporate on the 

 steam bath, dry for 30 minutes in the oven at 100°C. and weigh as potassium platinic 

 chlorid; calculate to potassium chlorid. To the weight of potassium chlorid add 

 0.00051 gram for every 10 cc. of amyl alcohol used in the extraction of the lithium 

 chlorid, which corrects for the solubility of the potassium chlorid in amyl alcohol. 

 Calculate to potassium. 



The weight of sodium chlorid is found by subtracting the combined corrected 

 weights of lithium chlorid and potassium chlorid from the total weight of the 3 

 chlorids. Calculate the sodium chlorid to sodium. 



PHOSPHORIC ACID.— OFFICIAL. 



50 REAGENTS. 



The reagents used are described under I, 7. 



51 DETERMINATION. 



Treat 500 cc. of the water, or a larger amount if necessary, with about 10 cc. of 

 concentrated nitric acid and evaporate in a porcelain dish nearly to dryness to drive 

 off hydrochloric acid. Treat the residue with water and filter, if necessary. Add 

 ammonium hydroxid to alkalinity and then just enough nitric acid to restore acidity. 



