MEDICO LEGAL COXTillEUTiOXS OX ARSEXIC. 
439 
III. Method for determining the Weight of Arsenic^ and 
making the Characteristic Tests. 
1. Determination of the weight of Arsenic. —The solution 
obtained as just directed is to be diluted with water, placed 
in a beaker, together wdth the washings of the porcelain 
dish, and a stream of washed sulphydric acid passed into it. 
If any arsenic is present, it will be precipitated in the form 
of tersulphide of arsenic. 
This is to be collected on a small filter (previously dried 
at %\9T F. and weighed), then thoroughly washed, and dried 
at the same temperature as before, and again weighed. The 
increase in the weight of the filter represents the amount of 
tersulphide of arsenic present. 
Or the precipitate may be collected on a small filter 
thoroughly washed, then dilute ammonia added drop by 
drop, until it is all dissolved; the filtrate and the washings 
are to be collected in a weighed dish, and evaporated to dry¬ 
ness and w’eighed as above. 
Each part of persulphide of arsenic is equal to 0*8049 of 
arsenious acid, or to 0*6098 of metallic arsenic. 
Thus, supposing the weight of the sulphide of arsenic 
was 0*345 grains, this is equal to (0*345 x 0*8049) = 0*277 
grains arsenious acid, or to (0*305 x 6098) = 0*210 grains 
metallic arsenic. 
2. Conversion of the Sulphide of Arsenic into compounds suit- 
able for testing. —It is now desirable to make the most cha¬ 
racteristic tests for arsenic; some of them are popularly 
known, and it is expected by courts of justice that they 
shall be made when arsenic is found in the examination of a 
case of suspected poisoning; there are others less known, 
but at least equally distinctive. Now, although it is not 
necessary to make them all to satisfy a chemist of the 
presence of arsenic, yet, as in the majority of cases, there is 
a sufficient quantity present to make all those tests which 
are deemed satisfactory by medical jurists, and as it con¬ 
sumes but little time, is it not as well to make all, or at least 
the greater part of them? Any common test ou)itted is 
often seized by the defendant’s counsel, and is made to 
appear as the most characteristic, if not the only reliable 
test. Why not avoid even this slight perplexity? Besides, 
otherwise the jury may be misled. Again, an accumulation 
of tests perfectly corresponding with and corroborating each 
other, is more satisfactory to them. 
In fact, the production of a metallic mirror, easily "vola- 
