70 
only toarsenic. This substance, so well known of old to the 
criminal poisoner as an agent that might be introduced into 
the system without fear of detection on account of the small 
quantities required to produce a deadly effect, is now not only 
detected by chemists in quantities that could not produce a 
poisonous effect, but by the microscope in such small pro- 
portions, that even a quantity accidentally introduced by 
medicine or other sources can be easily recognised. When 
chemical reagents fail clearly to indicate the presence of 
arsenic, the process of reduction may be employed, and the 
sublimate on the sides of an ordinary glass tube will by 
the aid of the miscroscope yield conclusive evidence under 
the powers of the microscope of the presence of arsenic. We 
give here from Dr. Taylor’s book the appearance of 
sublimated arsenious acid under a glass magnifying 30 
diameters (fig. 1). 
A solution of the same.substance will throw down cteaeds 
by evaporation, which present the same unmistakable forms 
as presented by the engraving, showing the same under a 
power of 20 diameters. 
Fig. 9. 
Crystals of arsenious acid by sublima- Crystals of arsenious acid, mag- 
tion, magnified 20 diameters. nified 124 diameters, p. 203. 
It is calculated that =,,,th of a grain of arsenic may be 
detected in solution by chemical tests, but the microscopical 
test is said to be applicable equally to ;,3,;th of a 
grain. 
What is true of arsenic is also true of other poisonous agents 
belonging to the mineral kingdom. Thus corrosive sublimate, 
the bichloride of mercury, and tartarised antimony, the 
potassio-tartrate of antimony, have both been too peculiarly 
brought before the public as agents by which the secret 
poisoner seeks to produce a destructive effect on the lives of 
