s is Reinsch's, which
is performed as follows: The suspected liquid is put in a little glass
test-tube with some hydrochloric acid. Then a small bit of bright copper
is dropped in, and the test-tube is held over a flame.

Now, arsenic has the wildest love for copper, and every trace of it in
the tube flies to the slip of copper and covers it with a grey coat.
Another metal does the same, certainly, but they can be distinguished
subsequently.

Presently the copper is removed, washed, dried, and placed in a tough
glass tube, very narrow at one end. This is held over a flame and
carefully heated, and then a phenomenon, not unknown, either, in the
loves of mortals, occurs. The arsenic abandons the copper, and clings in
crystals to the sides of the glass tube, where it can be recognised by
the aid of a magnifying-glass or microscope; and if the crystals are
heated with a bit of acetate of potash the odour drives the chemist from
the room.

To this curious fact, that arsenic loves copper when it is wet with warm
hydrochloric acid, and hates it when it is hot and dry, is due the
discovery of many a crime.

It is already plain to the reader that the analyst's task is not an easy
one. Sometimes the analytical examination is of vast extent; sometimes
it is greatly narrowed by hints from the family doctor. These hints are
interesting, and show that the doctor is, when he knows his business, a
real and a very skilful detective.

The doctor's eye is a wonderful one. When he enters a room, he not only
measures the patient from head to toe, notes the colour of his face, the
posture of his body, the signs of pain, stupor, or perhaps sham; but
observes the manner of the other people present, and sees every bottle,
glass, and cup in the place.

Now, although sudden death is usually from natural causes, when it
occurs soon after food there is always suspicion, as we have said. So,
if the doctor perceives great pain and nausea, he thinks of arsenic,
antimony, tinned meats, mushrooms, toadstools, and other things; if the
pupil of the eye is as small as a pin-head, and the sick man is drowsy,
he thinks of opium; if something seems to have caught hold of the
patient's heart, and to be squeezing it like a sponge, he thinks of
digitalis; if the poor victim is being worked like a puppet, and his
pupils are large with fear, he thinks of strychnine; if there is great
thirst, colic, and cramps in the legs, he thinks of lead.

[Illustration