478 
DE. A. w. hof:maaes’ ox the phosphoeus-bases. 
The crystals are long needles ; the faces T 1 0 are often but little developed (Fig. 43) ; 
the crystals have then a monoclinic aspect ; but the measurement of the angles 110. 101 
and T 1 0, 101 has furnished nearly the same result ; and moreover, on examining the 
crystals with the polarizing microscope, the line [0 1 0] is found to be nearly one of the 
axes of elasticity. 
The angle 101, 1 0 1 is so near to 90°, that there might appear some reason for regard- 
ing the crystals as dimetric hemihedrals. I am not, however, of this opinion, for I have 
observed only two cleavages, 110, 110, instead of the four corresponding to the dimetric 
system ; moreover the angle 101, 101 ahmysheen found a little greater than 90°. 
The needles, when small, are transparent ; the larger ones are rather milky, and hollow 
inside. 
The lustre of the faces 1 0 1 is slightly nacreous ; that of the faces 1 1 0 is -vitreous.” 
The di-iodide, as already observed, is very much more soluble in boiling water than 
in cold water. 100 parts of boiling water dissolve 458-3 parts of the salt, of which only 
3-08 parts remain in solution at 12°. A remarkable character of the salt is its insolu- 
bility in moderately concentrated solution of potassa; the dilute solution mixed with 
potassa immediately yields a crystalline precipitate ; the same property is exhibited, as 
is well known, by the iodides of tetrethylammonium and of the other ammonium- and 
phosphonium-metals. The solution of the di-iodide, like those of the diphosphonium- 
salts in general, is perfectly neutral ; it is colourless when first prepared, but on expo- 
sure to light, soon acquires a tint of yellow, and finally turns brown ; at the same time 
depositing a reddish compound, doubtless analogous to the periodides, which, as I 
observed some time ago, are formed under similar circumstances from the iodides of 
tetramethyl- and tetrethyl-ammonium, and which have since been so successfully studied 
by Weltzien. This red compound is immediately precipitated on adding a solution of 
iodine to the colourless solution. The di-iodide, like most diphosphonium-compounds, 
exhibits great stability. It melts, without the slightest decomposition, at 231°, and 
solidifies, with crystalline structure, a few degrees lower. 'NYhen more strongly heated 
over an open flame, it is decomposed, uith formation of a red-broum substance, which 
I have not examined. On distilling the di-iodide with excess of caustic baryta in an 
atmosphere of hydrogen, triethylphosphine passes over ; no gaseous product is formed 
in this reaction. Together with iodide of barium which remains behind, and triethyl- 
phosphine which distils over, oxide of ethylene is probably formed in this reaction. 
-f Ba, O = 2 Ba I + 2 [(C, B.,), P] -f (C, BJ O. 
(C2H5)3PJ 
I should, however, state that I have not succeeded in tracing experimentally the 
formation of oxide of ethylene. 
An attempt to decompose the solution of the di-iodide with sodium-amalgam was 
unsuccessful ; the salt, which is likewise but sparingly soluble in solution of soda, imme- 
diately separated out, and no appearances were observed which might have indicated 
the formation of the ammonium-amalgam. It is worthy of remark that no substituted 
ammonium-amalgam has yet been produced. 
