214 METAL-ORGANIC COMPOUNDS.
original form — should have originated in the discovery of these very metal-
organic compounds. It was not until Frankland (1853) had recognized that
the saturation capacity of the metals in these compounds could be measured
by the number of univalent organic radicals which are joined directly to the
metal atom that this combining capacity began to be regarded as a funda-
mental property of the metals — as well as of all other elements — which
governs their behavior in all of their compounds.
- Zinc Ethyl. Zn(C 2 H 5 ) 2.
Zinc and ethyl iodide when heated together combine to form ethyl-zinc
iodide:
Zn + I.C 2 H 5 = C 2 H 6 .Zn.I,
and upon stronger heating the ethyl-zinc iodide is transformed into zinc
ethyl and zinc iodide:
2 C 2 H 6 .Zn.I = Zn(C 2 H 5 ) 2 + Znl 2.
The formation of ethyl-zinc iodide, which does not always prove success-
ful when zinc alone is used, can be accomplished with certainty if instead
of zinc an intimate mixture of zinc and copper (zinc-copper couple) is
employed.
Zinc ethyl takes fire spontaneously when it comes in contact with the air,
and it is, therefore, a dangerous substance. Above all, care should be taken to
prevent its coming in contact with the skin, for the burns produced heal
only with difficulty. With suitable precautions, however, it is possible to
work quite safely with zinc ethyl; it can, for example, be transferred from
one vessel to another without danger if a plentiful supply of carbon dioxide is
allowed to flow over the openings as well as to fill the interiors of the
vessels.Place an intimate mixture of 100 g. zinc dust and 12 g. of finely
powdered and sifted copper oxide in a glass tube of 2.5 cm. diam-
eter. Lay the tube in a shallow trough of asbestos paper over
a row burner and pass into it a stream of dry hydrogen. After
proving the purity of the hydrogen, heat the mixture gently,
allowing the flames to only just touch the asbestos. During the
reduct'on the mass becomes lighter in color and swells up to a
considerable extent; on this account the tube ought not to be
more than half filled with the mixture at the outset. At the end
of half an hour, if no more water vapor escapes from the tube,
extinguish the flame and allow the material to cool in an atmos-phere of hydrogen.
Place 100 g. of this zinc-copper mixture and 100 g. of ethyl
iodide in a 200 to 300 c.c. Erlenmeyer flask and attach a return