SEPARATION OF ARSENIC. 
61 
grains of pure arsenious acid were dissolved in carbonate of 
potassa, and diluted with water, until the mixture made ten 
drachms, so that each drachm contained one grain of arsenious 
acid. 
a. One drachm of this solution, and consequently one grain 
of arsenious acid, diluted with six ounces of water, (constitu- 
ting 2tVo P arts ?) g ave a flame altogether blue, and a very 
strong film of metal. 
b. One half of a grain of arsenious acid, in eight ounces of 
weak acid, ( T - 6 \^ parts,) gave a flame slightly blue, but never- 
theless a strong film upon the porcelain. 
c. One drachm of the preceding liquor was diluted with 
water until the mixture weighed two ounces. To one drachm 
of this (consequently ^ of a grain of arsenic,) four ounces of 
weak acid were added, ( T ^.i~ parts,) and it still gave a flame 
visibly blue, and a film of arsenic sufficiently well marked. 
d. One-half of a drachm of the preceding liquor (8.), which 
contained consequently one-half of a grain of arsenious acid, was 
diluted with two pounds of water, and one ounce of hydro- 
chloric acid, added to this liquor (thus constituting no more 
than ^q-^qo parts;) from this I obtained an evident grayish 
black film, and in as many spots as I wished. 
e. One drachm of this weakened liquor, (d.), increased by 
sufficient weak acid to form two ounces, (thus forming but 
___i T __ part,) exhibited on a brilliant white enamel, a yellow 
spot although not recognisable in the gas. By directing for 
a long time the flame upon the same place, the bright yellow 
became a little deeper, and then changed immediately to a deep 
gray. 
A dilution of 500.000 times appears to be the limit of cer- 
tainty in the reaction by this method, and, in fact, this 
sensibility is so enormous that we ought to use great care lest 
we be misled by any residue from a former experiment; 
new portions of zinc should be used for every trial; the 
vessels should be washed with the greatest possible care; 
and the experiments should be made with materials perfectly 
pure, to assure the exactness of the results. The sulphuric 
