In the phosphines and their derivatives, which we have investigated from, time to time, considerable uncertainty has always attended the determinations of phosphorus by the ordinary methods recommended for the purpose. In fact, we never felt any confidence in the result, for no matter how carefully the determinations were made, duplicate analyses led to different numbers.

The uncertainty depends partly upon the difficulty of oxidising the phosphorus in such compounds to phosphoric acid. For, as a rule, in any dry combustion process which may be employed, volatile oxidation products, containing phosphorus, are formed of great stability, which frequently pass over the red-hot oxidising mixture almost unchanged. Moreover, the glass of the tube is attacked by the oxidising mixture, and this undoubtedly leads to inaccuracies, probably of considerable magnitude.