240 METHODS OF ANALYSIS. 



(c) WATER-SOLUBLE LEAD OXID. 



Place 2 grams of the lead arsenate in a flask with 2,000 cc of carbon dioxid free 

 water and let stand ten days, shaking eight times a day. Filter through a dry filter 

 and use aliquots of this for determining soluble lead and arsenic oxids and soluble 

 solids; determine lead as described above for total lead, using the same relative pro- 

 portions of sulphuric acid, water, and alcohol, but keeping the volume as small as 

 possible. 



(/) WATER-SOLUBLE ARSENIC OXID. 



For this determination use 200 to 400 cc of the water extract obtained under the 

 determination of soluble lead oxid. Add 0.5 cc of sulphuric acid and evaporate it 

 to a sirupy consistency, then heat on hot plate to appearance of white fumes. Add 

 a very small amount of water and filter off lead through the very smallest filter paper, 

 using as little wash water as possible. Place this filtrate in an Erlenmeyer flask, and 

 determine arsenic as described under total arsenic oxid, using the same amount of 

 reagents and the same dilutions. 



(</) SOLUBLE SOLIDS OR IMPURITIES. 



Evaporate 200 cc of the water extract obtained above to dryness in a weighed plati- 

 num dish, dry to constant weight at the temperature of the boiling water bath, and 

 weigh. The soluble solids so obtained represent principally any sodium acetate or 

 sodium nitrate present, with a very small quantity, perhaps, of lead acetate or nitrate 

 and some soluble arsenic, probably in the form of lead arsenate. 



(h) FORM OP STATING RESULTS. 



Per cent. 

 Moisture 



Total arsenic oxid 



Total lead oxid 



Soluble impurities (exclusive of soluble lead oxid and arsenic oxid) 



Total 



Soluble arsenic oxid 



Soluble lead oxid.. 



