126 CONTRIBUTIONS TO CHEMISTRY AND MINERALOGY. [bull. 167. 
(PNCl 2 )n, and a small amount of a chloronitride, P G N 7 01 9 , not belonging 
to the above series. The absence of the lower members, PNC1 2 and 
(PNC1 2 )2, is remarkable, and theoretically significant. Indications of 
a trace of a substance more volatile than the compound (PN01») :! ami 
of similar but stronger odor, were observed, but there is no evidence 
that it consists of one of the missing bodies. 
One of the most remarkable properties of the phosphonitrilic chlo- 
rides is that each member of the series is converted by heat into the 
rubber like polyphosphonitrilic chloride, a body, or mixture of bodies, 
of very high molecular weight, which is highly elastic and insoluble in 
all neutral solvents, but which swells enormously in benzene, and 
which, on distilling at a higher temperature, breaks down into a mix- 
ture of all the lower members mentioned above, which can then be 
separated by appropriate means. In this way it is possible to convert 
any phosphonitrilic chloride quantitatively into any other by heat and. 
distillation alone. In preparing any desired member, therefore, we are 
not limited to the quantity obtained from the first reaction product, 
but may work the residues over and over again until completely con- 
verted into the body sought after. With the exception of a few cases, 
in which the number of members is limited, as the aldehydes and 
cyanic acids, this series is therefore unique; I know of no other series 
of inorganic compounds in which this is possible. Polymerization 
takes place slowly, but perceptibly, at 250°, and is almost instan- 
taneous at 350°, while depolymerization begins at about 350°, and is 
rapid at a temperature close to incipient red heat. Triphosphonitrilic 
chloride, P 3 N 3 C1 G , is the ouly member which can be distilled in consid- 
erable amount at atmospheric pressure without considerable polymer- 
ization, and even this polymerizes almost completely on long boiling; at 
760 millimeters pressure the tetra-compound, P 4 N 4 01», boils at 328.5°, a 
temperature at which polymerization occurs quite rapidly, but this, as 
well as the penta compound, P 5 N 5 Cl 1(b and the hexa-compound,P 6 N b Cli 2 , 
can readily be distilled at 13 millimeters; the hepta-compound, P 7 N 7 C1 14 , 
suffers marked polymerization on distilling even at this pressure, and 
its isolation is therefore attended with much loss. Owing to the rapid 
change at higher temperatures, 1 have been unable to isolate any of 
the higher members, which remain as a considerable oily residuum, 
and there seems to be but little probability of this being effected by 
any known method, unless by distilling in a nearly absolute vacuum. 
The greatest difficulty in the separation of the members is caused by 
polymerization. It requires but a small amount of polyphosphonitrilic 
chloride to cause the liquid to thicken or gelatinize, and therefore to be 
incapable of further distillation, and some of this body is always 
formed in the course of a prolonged fractioning of the higher members. 
It was found, however, that this polymer is much more easily attacked 
by water than the lower members; when signs of polymerization are 
observed, it is only necessary to interrupt the distillation, and heat the 
