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468                                              MEDICAL JURISPRUDENCE

them in water. There i# yet a third method by which the organic mixture is
evaporated and extracted with alcohol acidified with a little hydrochloric
acid. The alcoholic solution is then evaporated to dryness, and the residue
is dissolved in water to apply the tests for oxalic acid.

Tests.—1. A solution of barium nitrate gives a white precipitate of
barium oxalate, soluble in hydrochloric acid or nitric acid without

2.    A solution of silver nitrate gives a copious white precipitate of silver
oxalate, soluble in ammonia and nitric acid.

3.    Calcium chloride or sulphate gives a white precipitate, insoluble in
acetic acid, but soluble in strong hydrochloric acid.

4.    Lead acetate gives a white precipitate, soluble in nitric acid, but
insoluble in acetic acid.

5.   Potassium permanganate in an acid solution is decolourised and is
reduced to the colourless manganese salt.

6.   About 5 cc. of oxalic acid are mixed with 1 cc. of sulphuric acid
(1 : 2)  and 2 drops of 10 per cent copper sulphate solution; about 1 g. of

granulated zinc is then put into the mixture so as to form a zinc-copper
couple. After three minutes 2 cc. of concentrated sulphuric acid and 0.1 cc.
of a 2 per cent aqueous solution of resorcinol are added to the mixture. A
pale blue colour develops, which deepens on warming.

Medico-Legal Points.—In the form of oxalate of ammonium, sodium,
potassium or calcium, oxalic acid exists as a natural constituent of several
plants and vegetables, such as sorrel, rhubarb, cabbages, lichens and guano.
Hence it may gain access to the body through food and drugs of vegetable
origin. It often occurs as a constituent of the human urine, 0.02 gramme
(0.3 grain) being excreted in 24 hours.

Oxalic acid is largely used in calico printing, in the manufacture of
straw hats, and in cleaning brass and copper articles, and wooden surfaces.
It is used for removing writing and signatures from paper and parchment
documents. It is a common household remedy for removing ink stains and
iron moulds from linen.

Cases of accidental poisoning by oxalic acid have sometimes occurred
from it having been swallowed in mistake for a saline purgative of magne-
sium sulphate.

A young woman took 2 drachms of oxalic acid by mistake for magnesium sulphate
at about 8 ajn. on the 29th October 1930. Immediately she complained of burning
sensation in the mouth, throat and abdomen, and induced vomiting by tickling her
fauces. She vomited many times and two hours later she brought up a good quantity
of blood. She was removed to the King George's Hospital, Lucknow, where she was
found restless with a rapid pulse (132 per minute) and hurried respirations (52 per
minute). She complained of very severe epigastric pain. She had no difficulty in
swallowing, but experienced burning pain in the abdomen after swallowing liquids.
Excoriations were present on the tongue and the post-pharyngeal wall, but not on the
lips and gums. She vomited occasionally, and brought up a few streaks of blood with
the detached pieces of the mucous membrane. She was given lime water and morphine
hypodermically. She was discharged cured on the third day.

A case25 occurred at Amritsar where 30 grains of oxalic acid were used instead of
40 grains of tartaric acid in the manufacture of " Darling Seidlitz powders ". Due to the
prompt action of the Police Department, all the tins containing these powders were
confiscated from different areas in the Punjab, and no accidents occurred.

During recent years cases of suicide by oxalic acid poisoning, although
very few, have occurred in India due to its increased use as a remover of
stains on clothes and the ease with which it can be obtained at a druggist's
shop. Owing to its taste, it is rarely used for homicidal purposes'. In his

25.   Punjab Chemical Examinees Annual Eeport, 1929, p. 10.