1IOMK-MADE LEAD ARSENATE. 21 



precipitate of lead (-Inornate will be formed. If to a filtered portion 

 of the solution a little of the lead acetate or lead nitrate solution is 

 added and a white precipitate produced, it shows that the arsenic 

 salt is still in excess and more lead should be added. The objection 

 to all of these tests is that the liquid must either be filtered or allowed 

 to settle before the test can be applied, either of which takes consid- 

 erable time and extra utensils for the purpose. The test described 

 in the following directions for making lead arsenate has proven reli- 

 able and can be made instantaneously. 



DIRECTIONS FOR PREPARING LEAD ARSENATE. 



This method will give a good product, without any material waste 

 of chemicals, and will require a minimum amount of time. For 

 every pound of lead arsenate it is desired to make, use 



Formula A: Ounces. 



Sodium arsenate (65 per cent) 8 



Lead acetate (sugar of lead) 22 



Formula P>: 



Sodium arsenal o (<;."> per cent) 8 



Lead nitrate 18 



If the sodium arsenate employed is 50 per cent strength, use 10 

 ounces instead of S. Of the pure crystallized salt, 14 ounces would be 

 required to furnish the same amount of arsenic oxid as would be fur- 

 nished by the given amounts of the 50 and 65 per cent grades if they 

 actually contained these per cents. In only one technical sample 

 examined, however, was the arsenic oxid content over 45 per cent. 

 The formulas are based on lead acetate containing 60 per cent of lead 

 oxid and lead nitrate containing 66 per cent of lead oxid. 



Dissolve each salt separately in from 1 to 2 gallons of water a (they 

 dissolve, more readily in hot water), using wooden vessels. After 

 solution has taken place, pour slowly about three-fourths of the lead 

 art-tali or nitrate into the sodium arsenate. Mix thoroughly and 

 test the mixture by dipping into it a strip of potassium iodid test 

 paper/' which will turn a bright yellow if lead is in excess. If the paper 

 does not turn yellow, add more of the lead salt slowly, stirring con- 

 stantly, and test from time to time. When the solution turns the 

 paper yellow sufficient lead salt is present, but if it should occur that 

 the paper does not turn yellow after all the lead salt has been added 

 dissolve a little more and add until an excess is indicated. The 



" The solution of lead acetate may have a milky appearance. This will be no objec- 

 tion, aii'l il need not be filtered. 



b If potassium iodid test paper can not be obtained it may be prepared by dissolving 

 a few crystals of potassium iodid in about, a tableBpOOnful of water and saturating 

 filter paper or blotting paper with this sol ut ion. After the paper has dried, cut into 

 strip* ami keep dry until needed. 



