620 FROF. LETTS AND MR R. F. BLAKE ON 



caustic potash or caustic baryta solution. This is then decanted off and acidulated with 

 hydrochloric acid, when dibenzyl phosphinic acid is precipitated, but in a very impure 

 condition, and only a small quantity is obtained. The reaction occurring between 

 benzyl alcohol and a mixture of phosphorus and its iodide yields it in large quantities, 

 and with ease. We have on p. 612 described this reaction, and have explained how the 

 crude dibenzyl phosphinic acid is separated. 



In order to purify it, the crude product is thoroughly washed with water and 

 recrystallised from boiling alcohol. 



Properties. — Dibenzyl-phosphinic acid is a colourless substance, almost insoluble in 

 water, but fairly soluble in hot alcohol. It crystallises from the latter solvent in very 

 thin iridescent plates, which, when dry, have a mother-of-pearl lustre. Its melting point, 

 determined with an Anschutz thermometer, was found to be 192° C. Heated above its 

 melting point, it decomposes, but also partly volatilises unchanged. Heated with 

 pentachloride of phosphorus, it appears to decompose, and to give among other products 

 chloride of benzyl. It forms a number of very characteristic salts, many of which are 

 beautifully crystalline. 



Analysis* 



r 1-4058 C0 2 = 0-3834 C = 67-99 per cent. 

 •5639 gave \ 03315 H 2 6 = 0-036833 H= 6-53 

 1 0-2639 Mg 2 P 2 7 = 0073701 P = 13-06 



Obtained. Calculated for (C 7 H 7 ) 2 HP0 2 



Carbon, 67'99 68-29 



Hydrogen, 6'53 6-09 



Phosphorus, .... 13-06 12-60 



Salts. — 



Barium Dibenzyl Phos%)hinate, {(C 7 H 7 ) 2 P0 2 } 2 Ba,8H 2 0. — This salt was obtained by 

 neutralising a hot and concentrated solution of caustic baryta with the acid, filtering 

 from a few insoluble flakes,t and allowing the solution to cool, when very thin plates 

 separated with the lustre of mother-of-pearl. The mother-liquors, on spontaneous 

 evaporation, gave large and very beautiful thin plates, radiating from a common centre. 



Analysis. 



(1) 0-4637 grms. lost at 110° C, 0-0855 = 18-43 per cent. 



(2) 1-1392 „ „ „ 0-2112 =18-53 

 11392 grms. gave 0-3439 BaS0 4 = 02022 Ba. = 1774 



Obtained. 



Calculated for 

 {(C 7 H 7 ) 2 P0 2 } 2 Ba,8H 2 



I. 



ii. 



1853 



18-43 



17-74 





Water, . . . 18-53 18-43 ' 18'67 



Barium, . . . 1774 ... 17-76 



The salt effloresces in dry air. It is soluble in alcohol. 



* The combustion was made with pure oxide of copper, and the phosphorus determined as described at p. 556. 

 t We do not know to what these are due. 



