1872.] Dr. A. W. Hofmann on the Phosphorus Bases. 231 



water, alcohol, and ether. These solutions have a decidedly acid reaction. 

 The crystals melt at 76° ; at a higher temperature they are volatilized 

 •without decomposition ; indeed the distilled product shows the same 

 melting-point as the undistilled acid. Dimethylphosphinic acid is less 

 suitable for analysis than the mono-compound. It appeared sufficient 

 to fix its composition by the examination of the silver- salt. This analysis 

 proved the acid to be represented by the formula 



C 2 H 7 P0 2 =(CH 3 ) 2 HP0 2 . 

 It is thus seen that dimethylphosphine, when treated with nitric acid, fixes 

 not three atoms of oxygen, like the monomethylated base, but only two. 

 Dimethylphosphinic acid forms only one series of salts, having the general 

 formula 



C 2 H 9 MP0 2 = (CH 3 ) 2 MP0 2 . 



Silver Dimethylphosphinate. — This salt is obtained by saturating the 

 crude acid still retaining hydrochloric acid with silver oxide, evaporating the 

 filtered solution, and precipitating the concentrated liquid with absolute 

 alcohol. The salt presents itself in the form of fine felted white needles 

 extremely soluble in water, but very slightly so in ether and absolute 

 alcohol. Its composition is represented by the formula 



C 2 H e AgP0 2 =(CH 3 ) 2 AgP0 2 . 



Barium Dimethylphosphinate. — By boiling the solution of the pure acid 

 with an excess of precipitated barium carbonate, a neutral liquid is obtained, 

 which, when evaporated on the water-bath, dries up to a transparent var- 

 nish. In contact with a hard body this clear varnish becomes opaque, and 

 shows inclination to crystallize. It is soluble also in alcohol. 



Lead Dimethylphosphinate.— The preparation is conducted in the same 

 manner as that of the barium salt, only that oxide instead of carbonate is 

 employed. In its properties it resembles the barium salt : the varnish 

 dissolves in a small quantity of water ; the solution becomes turbid, how- 

 ever, by the addition of a larger quantity. . Several lead determinations 

 showed excess of lead above that contained in the normal dimethylphos- 

 phinate, a result which cannot surprise if the tendency of lead to form 

 basic salts and the absence of all properties warranting the purity of the 

 compound be considered. 



It is of some interest to compare the behaviour of phosphoretted hydro- 

 gen under the influence of powerful oxidizing agents with that of its several 

 methylated substitution -products. Phosphoretted hydrogen, on treatment 

 with concentrated nitric acid, fixes four atoms of oxygen, becoming con- 

 verted into tribasic orthophosphoric acid ; methylphosphine similarly treated 

 combines with only three atoms of oxygen, forming dibasic methylphos- 

 phinic acid. Under the same conditions dimethylphosphine appropriates 

 not more than two atoms, giving rise to monobasic dimethylphosphinic acid. 

 Lastly, trimethylphosphine fixes but one atom of oxygen, the product of 

 the reaction being trimethylphosphine oxide, observed some years ago by 



s 2 



