ACCURACY OF NEUMANN’S METHOD. TD 
traceable to an indistinct end-point. Neumann’s method 
was especially developed for the analysis of organic sub- 
stances and in connection with a process for the combustion 
of the organic matter and the conversion of the phosphorus. 
into phosphates by means of oxidising acids. The organic 
substance is oxidised by heating with a mixture of equal 
volumes of concentrated nitric and sulphuric acids, renewed 
as required. The oxidation is complete when the acid 
mixture remains clear and almost colourless after the boil- 
ing off of all the nitric acid. Neumann calls the product 
obtained an ‘‘acid-ash.’’ By this process the well known 
danger of loss of the phosphorus of organic compounds by 
volatilisation during ignition is entirely obviated. The 
phosphate in this acid-ash, which must not contain more 
than a certain maximal amount of Sulphuric acid, is pre- 
cipitated as ammonium phosphomolybdate in the presence 
of ammonium nitrate (107%) by the addition of an aqueous 
solution of ammonium molybdate. The precipitate is washed 
acid-free by decantation with ice-cold water, dissolved in 
excess of seminormal sodium hydroxide, the ammonia is 
boiled off, and the excess of alkali is determined by titration 
with seminormal sulphuric acid. Neumann takes the equa- 
tion given above as correctly representing the reaction 
which occurs with the alkali, and according to this each 
cubic centimetre of seminormal alkali interacting with 
the ammonium phosphomolybdate corresponds to 1°268 
milligrams of P,O;. 
Plimmer and Bayliss have modified Neumann’s acid-ash- 
ing process by adding a definite volume of concentrated 
sulphuric acid at the beginning of the oxidation process, 
and putting in nitric acid from time to time as required 
until the oxidation is complete. This avoids the difficulty 
of limitation of the amount of acid mixture, which, in the 
case of substances containing much fat and carbohydrate, 
such as milk, is rather a serious disadvantage. Plimmer 
