46 ON THE ALLOYS OF COPPER AND ZINC. 
of hydrogen before weighing it. That this operation is of the first importance 
is, however, well known to the analysts of this vicinity, who have long been 
accustomed to apply it in practice.* It is necessitated less, as it appears to me, 
by the oxide of copper formed during drying, — for the bright surfaces of the 
copper precipitated by this method remain untarnished when rapidly dried at 
temperatures even as high as 110° to 115°,—than by an impurity consisting of 
organic matter derived from the iron; either carbon, or perhaps some one of the 
offensive hydro-carbons which are generated during the action of acids upon iron, 
which may adhere to the spongy copper. At all events, if a portion of the pre- 
cipitated copper which has been dried at 100^— or at any temperature lower than 
that at which oxidation occurs — be placed, as was suggested to me by Mr. Dick- 
inson, in a bulb tube with narrow outlet, such as is used in testing for arsenic, 
and heated in the flame of a spiritlamp, it will be found that a quantity of 
water collects in the narrow part of the tube, while the copper becomes lustrous 
and assumes the bright red color proper to it. At first sight it would appear 
as if this behavior was produced by the reaction of a portion of the spongy copper 
upon the oxide of copper with which it might be soiled, in which event a small 
quantity of suboxide of copper would be formed, the color of which could hardly 
mask, to any extent, that of the pure copper. But on examining the reaction 
more attentively I have found that carbonic acid as well as water can readily 
be detected in the atmosphere expelled from the tube in which the copper is 
heated ; a distinct empyreumatic odor is at the same time perceptible. I have 
also several times observed traces of ammonia. This gas is always evolved in 
considerable quantity when the dirty copper is heated in an atmosphere of hydro- 
gen; the aqueous vapor driven off in this case being strongly alkaline from its 
presence. Organic matter must therefore have been attached to the spongy copper, 
and the lustre which the latter acquired when heated may have been occasioned 
by the simple expulsion of the impurity, or in part by the reduction of oxide 
of copper by it. | i 
That the phenomenon does not depend upon the presence of free carbon seems to be 
proved by the fact that portions from the exterior of a mass of spongy copper, which 
had been protected from contact with the iron by a layer of copper nearly an inch in 
thickness, were found to exhibit reactions similar to those just described, water and 
empyreuma being evolved when the dry copper was heated in a closed tube. Indeed, 
* In lieu of this, some assayers convert the precipitated copper into oxide, and weigh the latter. 
