ACCURACY OF NEUMANN’S METHOD. 85 
acid still further increases the amount of molybdenum 
found in this precipitate, the amount increasing with the 
quantity of sulphuric acid present until according to Hissink 
and van der Waerden, a maximum of 12°65 Mo for each P 
is reached. Richardson, and Artman state that the pre- 
cipitate formed in the presence of sulphuric acid or a sul- 
phate always contains sulphate, even after being washed 
till neutral. Richardson supposes that sulphuric acid may 
to a certain extent form a sulphomolybdate analogous to 
the phosphomolybdate, and which would react towards 
alkali like the latter. In the precipitate prepared as 
described above, however, I have not been able to detect 
more than traces of sulphate after complete washing. The 
precipitate was dissolved in sodium hydroxide and the 
ammonia boiled off. The solution was acidified with 
hydrochloric acid, and barium chloride was added. 
Richardson, and Artman simply dissolved the precipitate 
in nitric acid and then tested with barium chloride. 
The conditions under which the precipitate of ammonium 
phosphomolybdate is formed in Neumann’s method for the 
estimation of phosphorus thus seem to be particularly 
favourable to the appearance ofa precipitate containing 
excess of molybdenum. I have, therefore, determined 
the amount of molybdenum contained in the precipitate 
formed under these conditions in order to discover what 
part of the error observed may be due to excess of molyb- 
denum, as this would enable the precipitate to react with 
a larger amount of alkali than that assumed by the formula 
given above and therefore lead to high results in the 
estimations by Neumann’s method. 
Molybdenum-content of precipitate of Ammonium 
Phosphomolybdate. 
After trying several methods for the estimation of 
molybdenum, the method given by Brearley and Ibbotson 
