a ° =m 
86 H. S. H. WARDLAW. 
for the estimation of phosphorus was adopted. In this. 
method the precipitate of ammonium phosphomolybdate is. 
dissolved in ammonium hydroxide, the solution is nearly 
neutralised, and the phosphate and molybdate are precipi- 
tated together as a mixture of lead phosphate and lead 
molybdate by the addition of lead acetate. The phosphate 
is said not to be precipitated quite completely in this way,,. 
but as the lead phosphate formed amounts to only 10% of 
the whole precipitate the error introduced is not large. 
Knowing the amount of phosphate present we may calculate 
the weight of lead phosphate which should be formed, and 
by subtracting this from the total weight of the mixed 
precipitate we may obtain the weight of lead molybdate 
thrown down. The following are the details of an estimation. 
The precipitate of ammonium phosphomolybdate obtained 
as described above from 10 cc. of standard phosphate solu- 
tion was washed acid free with iced water and dissolved in 
ammonium hydroxide, the solution was made up to 200 cc. 
and divided into two equal parts, each part being then 
treated independently. The ammonia was nearly neutral- 
ised with hydrochloric acid, about 20 gm. of ammonium 
chloride were added, the solution was heated to boiling, 
and 200 cc. of a boiling solution of lead acetate and acetic 
acid (16 cc. 50%, saturated, lead acetate and 16 cc. of 
glacial acetic acid made up to 1000 cc.) were poured in. A 
dense white precipitate immediately formed, and the boil- 
ing was continued for ten minutes toensure that the precipi- 
tate became granular. The precipitate is finely divided and 
very heavy, but when prepared as described it filters easily. 
The precipitate was washed free from chlorides with hot 
water and ignited with the filter in a muffle, very bigh 
temperatures being avoided as the precipitate is fusible. 
