48 THE PREPARATION OF ALKYL-SULPHINE, SELENINE, AND PHOSPHONIUM SALTS. 
first experiment we added silver oxide cautiously till the acid reaction disappeared, 
and then attempted to obtain the sulphine iodide by evaporation of the filtered neutral 
solution. Very little of the salt was obtained, although the residue of silver iodide was 
washed with hot water till the washings no longer gave an iodide reaction. On mixing 
this residue, however, with more silver oxide and water, we obtained a solution rich 
in the sulphine iodide; and it was found that the whole of the salt could be recovered 
in this way. This points to the fact that the iodides of such bases as triethyl-sulphine 
form insoluble double salts with silver iodide; and we were able to confirm this by 
separate experiments. These double salts differ in appearance from silver iodide 
itself, inasmuch as they are white in colour instead of yellow. An explanation is thus 
afforded of the change of colour from white to yellow, which the precipitate undergoes 
when silver nitrate solution is gradually added to a solution of any of these iodides of 
organic bases. 
Quantitative experiments have been made which verify the above equations. 
The yield obtained in one experiment, after finally converting the base into iodide and 
crystallising the salt out, was more that five-sixths of that indicated by theory. The 
identity of the salt was established by its general properties, and by an iodine 
estimation (found, 51.60 per cent. of iodine; calculated, 51.62 per cent.) The 
method has been tried and found to work when selenium is substituted for sulphur. 
In the case of phosphorus, the change which takes place during the heating is 
not quite so simple, though in appearance it is closely similar. Hither yellow or 
(preferably) red phosphorus may be used, and the ethyl iodide must be taken in 
somewhat large excess of the proportion of 7 C,H;I to 2 P. The tubes are heated, 
as in the case of sulphur, to 180°C for about 24 hours. All the phosphorus 
disappears, and a liquid or semi-solid mass of black polyiodide remains. That this 
cannot consist wholly of P (C,H;), I, is evident if one try to construct an equation, 
and our experiments proved that only half of the phosphorus employed is converted 
into this substance and recoverable as P (C,H;), I by the method already described, 
while the other half goes to form a compound that is converted into triethyl phosphine | 
oxide by the action of the hydrogen sulphide and water. The theory of the reaction 
which is represented by the following equations is in accordance with the quantitative 
results of our experiments :— 
(1) ON lene Opal = le (C,H;)4 I, + P (C,H;)s I, 
(2) F (C,H,).!1, + HS = P (C.H;),1 + 2HE+5 
P (C,H;); lL, + 9S + H,0 = P(C,.H,),0 + 4HI1+S8 
According to this theory, 3.1 grams of phosphorus should yield 13.7 grams of 
P (C,H;), 1, and the weight of the precipitated sulphur should be 3.2 grams. We 
obtained 13.45 grams of the iodide and 3.4 grams of precipitated sulphur. The salt 
