Dusart’s Method, as Modified by Blondlot
Dusart’s process takes advantage of the facility with which hydrogen combines with phosphorus. The substances under examination are placed between two asbestus stoppers in a tube, one end of which tapers to a point, and a current of pure hydrogen conducted over them. In presence of phosphorus the evolved gas will burn with a green flame, and, upon bringing this in contact with a porcelain plate, red spots will be deposited upon the latter. Blondlot prefers to introduce the suspected materials into the flask in which the hydrogen is generated. He employs the apparatus represented in Fig. 10: a is a flask for evolving hydrogen; b is a U tube, filled with fragments of pumice stone which are saturated with a concentrated solution of potassa; c is a Mohr clamp; d a screw-clamp; e a platinum jet. This jet is necessary in order to avoid a yellow coloration of the flame by the soda contained in the glass. Pure hydrogen is at first evolved, in order to ascertain that the flame is colorless and red spots are not produced when it is intersected by a cold plate. The purity of the reagents used having thus been confirmed, the clamp d is closed until the acid is forced back into f; and the materials to be examined are then added to the fluid. Upon opening the clamp the liquid passes from f into a, and the evolution of gas recommences. The gas is then ignited: the flame possesses the characteristic properties mentioned above, if the suspected substances contain phosphorus.