400 Intelligence and Miscellaneous Articles. 
properties of irou, but though this renders it probable, a priori, 
that the thermal conductivity might be changed, yet it does not 
necessitate such a change. The thermo-electric relation of iron is 
changed by magnetization; but the thermo-electric relation appears 
to be unconnected with thermal conductivity. — Proceedings of the 
American Academy of Arts and Sciences, May 29th, 1883. 
ON A NEW METHOD OF INSULATING METAL WIRES EMPLOYED 
IN TELEGRAPHY AND TELEPHONY. BY C. WIEDEMANN. 
Having had occasion during the past year to employ, for the 
decoration of jewellery and other objects of art, the processes 
described by Nobili and Becquerel for producing various colorations 
by means of baths of alkaline plumbates and ferrates, I observed 
that the objects thus coloured had become absolutely resistant of 
all galvanic action, that their surfaces once coated with the per- 
oxide of lead or iron were no longer capable of conducting the 
electric current. A copper or brass wire, or even one of iron, 
became thus covered with an insulating layer analogous to that 
of a coating of resin or of gutta percha. 
It appears to me that this process may prove of considerable use 
in the manufacture of cables or wires employed in telegraphy and 
telephony. It is easily effected and its cost is small. The coating, 
which resists in a very high degree all atmospheric influences, is a 
guarantee of its duration. The insulation is absolute. The mode 
of preparation is extremely simple : it suffices to prepare a bath of 
plumbate of potash by dissolving 10 grms. of litharge in a litre of 
water to which has been added 200 grams of caustic potash, and to 
boil for about half an hour ; it is allowed to subside and is then 
decanted, when the bath is ready for use. The metal wire to be 
coated with the peroxide of lead is attached to the positive wire, and 
a small platinum anode at the negative pole immersed in the bath ; 
finely divided metallic lead is precipitated at the negative pole, and 
the peroxide of lead is deposited on the metallic wire, which passes 
successively through all the colours of the spectrum. The insula- 
tion is only perfect when the wire has attained the final tint, which 
is a blackish brown. 
Thus coated the wire is perfectly insensible to all electric action ; 
perfectly cleansed objects may be attached to it and connected with 
the negative pole in a gold, silver, or nickel bath without the cur- 
rent, however powerful, having the slightest action on the objects 
to be coated with metal. A wire thus treated, placed in a current 
and brought in contact with another wire connected with a gal- 
vanometer, has not the slightest effect upon the latter; there is no 
diminution in the first current, which passes through the wire coated 
with the peroxide of lead. 
This perfect insulation may possibly be turned to account by 
electricians in the construction of various apparatus. — Comptes 
Bendus, Oct. 15, 1883. 
