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542                                                MEDICAL JURISPRUDENCE

nated in the urine of Hindus and Mahomedans and about five times th
amount excreted in the urine of Anglo-Indians.   The difference in the lead
content of the excreta appears to be due to the difference in the lead content
of the common food stuffs taken by different communities.

The   quantitative  method  of   determining  lead  in  urine  devised b
Francis, Harvey and Buchan4 and modified by Roche Lynch, Slater and
Osier 5 is as follows : —

Five hundred cubic centimetres of urine are measured out of a 24-hour samt>lo     A
evaporated to about 25 cc. and transferred to a silica flask, all the residue being \
out  from  the   evaporating  basin  with  about   20   cc.   of   concentrated   nitric  acic
dissolved by gentle heating.   After cooling, about 6 cc. of concentrated sulphuric

are added and heated with further addition of nitric acid, drop by drop, until corrml 1
oxidation takes place which is indicated by the absence of charring on further heat'
The free nitric acid present in the solution is given off by boiling strongly after diirrH
with about 40 cc. of water and adding about 25 cc. of saturated solution of amrnnn'

.                                                                                                   rnnn

exalate.   The heating is continued for some time more till it is reduced to a small K S
by the decomposition of excess of sulphuric acid and indicated by white fumes of sulWh
trioxide.                                                                                                                      puur

To the oxidation product 5 cc. of 10 per cent ammonium acetate and ammo '
citrate solutions are added and the mixture is rendered alkaline with ammonia.   It iq+k"*1
treated with 2 cc. of 5 per cent sodium cyanide solution and transferred to a i^n i
separating funnel and extracted with these portions of 0.1 per cent solution of
thiocarbazone in chloroform (about 20 cc. in all)  and three or four times
pure chloroform  (about 35 cc. in all)  until the last traces of the dye are     mn
removed from the aqueous mixture.   The combined extracts are washed with w-vta       ^
distilled to drive off chloroform.   The residue is oxidized by heating with 1 Cc C of   &
centrated nitric acid and a small crystal of potassium sulphate in a boiling water
for about thirty minutes after which 0.5 cc. of .concentrated sulphuric acid is add rl
the heating is continued over a low flame adding nitric acid, drop by drop, as r^ c
When oxidation is complete, the free nitric acid is driven off by boiling stronelv
water.   After cooling, it is diluted with 20 cc. of water and transferred to a 50 cc M    i
cylinder.   An exactly similar cylinder is selected for the standard lead solution a k       r
amount of which (0.01 mg. of lead per cc. of the solution) is carefully measured f   own
burette and run in the cylinder.   Five cubic centimetres of acetate solution are t        m
in both the cylinders.  To each cylinder are then added 2 cc. of 5 per cent sodiurn
5 cc. of 6N (approx.) ammonia, water to the 50 cc. mark and finally 2 drops of 4

sodium sulphide with constant stirring.   The brown colour developed in the first     r °5
is matched against the standard with the known amount of lead in the second     v n?er
By repeating the process of final matching with different amounts of standard git-'
an accurate comparison can be made to a limit of 0.005 mg. of lead,                    solutions

In these experiments the glassware,' reagents, and distilled water must be fr
lead or contain such small amounts of lead that they may be neglected.   Bla-nkx

.        a-n

minations should always be made to see if lead is taken up from the apparatm
other source during the course of the experiments.                                                or any

Chemical Tests.—!.   Hydrochloric acid produces  a white  preom"*
soluble in boiling water, and crystallizing on cooling.                          <-ipxtate,

2.   Hydrogen sulphide produces  a  dark brown  or  black
insoluble in ammonium sulphide but soluble in dilute nitric acid.

3.    Potassium iodide solution gives a bright yellow precipitate   c-nl w
in boiling water, and crystallizing on cooling into golden yellow span i

4.    Potassium chromate gives a yellow precipitate of  lead chr
which is insoluble in dilute but soluble in concentrated nitric acid,       mate»

5.    A drop each of a 1 per cent solution of pyridine in water a-M    *
mixture of 0.1 per cent gallocyanine and sodium bicarbonate added trT   A    *
of lead solution on a filter paper produces a deep violet colour.          a       P

Medico-Legal Points.—!.   Lead in the metallic form is not nm
but it is probably acted upon by the secretion of the intestine and         °US)
as a poison after it is absorbed into the system as a salt,   L^      .y .?ct
------------------------—-----------____________________________ -^aci missiles

4.   Analyst, Dec. 1929, p. 725.

5.   Analyst, Dec. 1934, p. 787.