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30
intensity to twenty such sperm candles, and each such gas
shall, with respect to its purity, be so far free from ammonia
and sulphurretted hydrogen that it shall not discolour either
turmeric paper or paper imbued with acetate or carbonate of
lead when these tests are exposed to a current of gas issuing
for one minute under a pressure of five-tenths of an inch of
water, and shall not contain more than twenty grains of
sulphur in any form, in one hundred cubic feet of gas; provided
that any Gas Company and the Local Authorities of
the district supplied by such Company shall be at liberty to
agree upon any other different test by which to ascertain the
purity of the gas, or to vary the amounts of ammonia or
sulphur in any form hereinbefore allowed, and thereupon the
Company shall be thenceforth liable to have the purity of
their gas tested in the manner so prescribed.