8 LEAD AKSENATE. 



using the same relative proportions 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 a 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 

 platinum 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, or sodium arsenate. 



These methods were not followed exactly in all cases, owing to 

 peculiarities of some of the samples. Those which were moist and 

 in the form of a paste were heated at about 85 C. till dry enough to 

 powder, and the loss noted. The analysis was then carried out on 

 this dried sample and the results calculated to the material in its 

 original condition. The moisture on the dried sample was calculated 

 to the original material and added to the loss obtained on the first 

 drying for " total moisture." 



Insoluble matter was that remaining from the treatment with nitric 

 acid and was removed by filtration, washed, ignited, and weighed. 



In case calcium is present in the sample, it may be separated from 

 the lead by treating the precipitated sulphates with water (acidified 

 with sulphuric acid) to which no alcohol has been added and filtering, 

 or by the following method, which is the one used in this work: 



Precipitate the lead from a solution slightly acidified with nitric acid, with hydrogen 

 sulphid in the cold; filter off the precipitate containing the lead sulphid, wash, 

 dissolve in moderately strong hot nitric acid, treat this solution with 4 or 5 cc of 

 concentrated sulphuric acid, carry down in a porcelain dish to expel nitric acid, treat 

 with water and alcohol mixture, and proceed as before. Calcium is determined in the 

 filtrate from the lead sulphid (after removing any arsenic remaining therein by hydro- 

 gen sulphid) by precipitating with ammonia and ammonium oxalate in the regular 

 way. 



In case the material was lead arsenite or contained this substance, it 

 was determined as follows: 



Boil 2 grams of the sample with 50 cc of dilute (1 to 5) sulphuric acid for about 

 one hour, cool, make up to mark, filter through dry filter, and to 50 cc of the filtrate 

 add sodium bicarbonate in considerable excess and titrate with standard iodin solu- 

 tion, using starch as indicator. The arsenic equivalent of the iodin solution used is 

 calculated as arsenious oxid 



Tests were made on the water soluble impurities for acetates and 

 nitrates. This would indicate which lead salt had been used in the 

 manufacture of the sample. 



