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SELECTED ARTICLES. 
4. If the arsenic be diminished, and does not represent more 
than the one-eight or ten thousandth of the liquor, the whole 
of the flame is not colored, but only its point. The lower 
three-fourths resemble the flame of pure hydrogen, while 
the point is tinged greenish yellow, and is opaque. If the 
porcelain be held in the bright part of the flame, the cooled 
arsenic becomes attached to it. It is hardly necessary to say, 
that this combustion is altogether analogous to that of olefiant 
gas, in which the separated carbon burns immediately at the 
circumference, or may be obtained in the state of lamp 
black by the aid of a cold body. The arsenic burns in a like 
manner when not collected, and is changed into arsenious 
acid, which is likewise deposited at the edges of the arsenical 
film. 
The change of color is so marked, that, having once observ- 
ed it, we may recognise immediately, by the inspection of the 
flame, the presence of arsenic, and afterwards find a confirma- 
tion by the use of the porcelain tile. 
5. The arsenic acid is reduced in the same manner as the 
arsenious; and the same may naturally be said of the arse- 
mates. A very small particle of arseniate of soda, held in the 
flame of hydrogen obtained from perfectly pure materials, 
instantly produced a light blue flame and a black film. 
6. Pure zinc, boiled with an aqueous solution of arsenious 
acid, becomes covered with brown spots, and finally with a 
thin film of metallic arsenic, the color of which becomes 
deeper and deeper. These particles of zinc, washed with 
pure water and placed in hydrochloric acid, likewise pure, 
produce an arsenical flame. This experiment explains readily 
why we cannot employ the zinc a second time in similar ex- 
aminations. 
7. Arsenic acid and zinc disengage immediately arsenuretted 
hydrogen, and the zinc becomes covered with a black pulve- 
rulent film, which is easily scraped off and which contains 
arsenic. 
8. I have made different experiments for the purpose of 
graduating the degree of sensibility of this reaction. Ten 
