On whitening Copper Plates with Vapour. 445 
bustion of yarious bodies; in colour it is gray or white, yellow 
or reddish. 
10. Flowers. A very fine pulverulent deposit, produced by 
the volatilization of certain substances, and which are attached 
to the stud, or to some cold body placed above. This deposited 
matter is sometimes a soot, as in coal, sometimes sulphur, and 
sometimes a metallic oxide: this last is of various colours: that 
of antimony and arsenic is white, and that of lead is yellow. 
The colour is permanent, as in the flowers of antimony ; or va- 
tiable according to the temperature of the oxide, as we see in 
the oxide of bismuth, which is yellow so long as it is exposed 
to the flame of the blowpipe, and white as soon as it cools. 
Lastly, we ought to observe the changes which the products 
of the experiments undergo some time after they are terminated, 
as in the enamel produced by the fusion of barytes, which spreads 
into small fragments a few hours after fusion. 
XCIIL. On the Phenomenon of Arsenic and other Bodies whiten- 
ing Copper Plates with their Vapour. By L.V. Braugna- 
TELLI™. 
Warn concrete arsenic is thrown upon burning charcoal it 
emits a white vapour, which may be condensed in a white crust 
on a plate of copper held over it. This has been considered as 
an exclusive characteristic of arsenic, and the most convenient 
practical mode of discovering its presence. An occasion offered _ 
of submitting this generally received opinion to the test of ex- 
perience, by examining the matter contained in the stomach of 
a young child which was subject to worms and accustomed to 
take calomel (mercurius dulcis). The concrete matter existing in 
the fluids of the stomach, being carefully separated, was found 
insoluble in water, and, when placed on burning charcoal, rose 
in a white vapour which whitened the surface of a plate held 
over it. Here there was no suspicion of arsenic, particularly as 
it was insoluble in water, and instantly recognised by other ex- 
periments tobe calomel. This mercurial preparation, therefore, 
whitens a plate of metal precisely like arsenic. Experimenting 
on several other bodies which produce this effect, I found that 
the vapour of phosphorus during combustion, that of oxymuriate 
of ammonia placed over burning charcoal, and the vapours from 
corrosive sublimate treated in the same manner, all whitened 
plates of copper ; the white spots appear to the eye almost iden- 
tical; at the moment they cannot be distinguished one from 
another, and may lead the most experienced observer into error. 
It is necessary, however, to observe, that the white spots made 
* Trom Furmacopea Generale, Pavia 18144. 
on 
