228 



Dr. A. W. Hofmann on the Phosphorus Bases. [Mar. 21, 



fectly concentrated and at moderate temperatures, that the liquid taken from 

 the tube and treated in an appropriate manner with magnesian salts gave 

 no precipitate whatever. If, on the other hand, strongest fuming nitric 

 acid be employed at high temperatures, phosphoric acid is certainly formed ; 

 but only when the reaction takes place at the verj' extreme temperatures 

 recommended by Carius* in his more recent paper, is the whole quantity 

 of phosphorus made precipitable by magnesian salts. 



It appeared of interest to submit to a closer examination the products of 

 oxidation that are formed by the action of nitric acid on the primary and 

 secondary phosphines at moderate temperatures, more especially since some 

 of these bodies have probably passed already through the hands of M. 

 Paul Thenardwhen engaged in his remarkable but, unfortunately, unfinished 

 researches on this subject. Experiment showed that nitric acid gives rise to 

 new acids of great stability and comparatively little volatility, and thus avery 

 simple method of estimating phosphorus in this whole group of compounds 

 at once suggested itself. It was only necessary to dissolve the substance 

 under examination, according to circumstances, either in strong hydrochloric 

 or in nitric acid, to mix the liquid slowly with fuming nitric acid, to treat the 

 .solution after evaporation with excess of sodium carbonate, and finally to 

 dry and fuse the mass in a porcelain crucible ; in this way the oxidation 

 of the phosphorus is easily and perfectly accomplished. All the phosphorus 

 estimations necessary in these researches have been performed in this 

 manner. 



Experiments in the Methyl Series. 



Monomethylphosphinic acid. — In order to obtain the product of oxida- 

 tion of methyl phosphine in appropriate quantity, a slow stream of the gas 

 was directed into fuming nitric acid. It would have been unnecessary in 

 this case to employ the phosphine gas in a state of purity ; it was suffi- 

 cient to make use of the methylphosphine as it is delivered from the crude 

 product of the action of methyl iodide on phosphonium iodide and zinc oxide 

 by treatment with water. This gas always contains small quantities of 

 phosphoretted hydrogen, which ignite in contact with the fuming acid, 

 and easily give rise to small explosions. As the methylphosphine becomes 

 purer, these become more seldom and at last quite cease. Invariably, 

 however, in consequence of these detonations, more or less phosphoric acid 

 is found amongst the products of oxidation. 



To get rid of the nitric acid, the solution is several times evaporated to 

 dryness on a water- bath, the residue dissolved in water, and the liquid 

 boiled with lead oxide for the purpose of separating the phosphoric acid ; 

 a lead-salt is thus formed which is insoluble in water but dissolves in acetic 

 acid, leaving an appreciable residue of lead phosphate. This solution is 

 freed from lead by means of sulphuretted hydrogen, and from acetic acid by 

 repeatedly evaporating, when the new body remains as an oily liquid which, 

 on cooling, solidifies to a crystalline mass resembling spermaceti. The 

 * D. Chem. Ges. Ber. 1870, p. 697. 



