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257
The Board also suggested the expediency of an alteration in
the standard of light prescribed by the statutes. The statutory
standard is obtained by burning a sperm candle of six to the
pound, at the rate of 120 grains an hour ; and the gas is
required to be of such lighting power as to produce,
when consumed at the rate of five cubic feet an hour, a
light equal to that produced by sixteen such candles. A
Committee, appointed by the Board of Trade, has reported
adversely to the continuance of the use of the sperm candle as a
standard, it having been proved that, in spite of precautions
taken to secure uniformity in the manufacture of the candles,
there remained considerable variation in their lighting power.
In the Reports of the Metropolitan Board for 1885 & 1886
no reference was made to the important matters dealt with in the
above paragraph, but in the Report for 1887, the subject is again
dealt with, and we are informed that in the interval a long series
of careful and complete experiments have been made by the
Officers of the Board, under the Board's authority, with the
result that the Pentane air-gas standard, as devised by Mr. A.
Vernon Harcourt, one of the gas referees, has appeared to
possess in a higher degree than any other, the merits of
simplicity, accuracy, and reliability. It is added that "the
Board has not yet formally expressed any opinion on the subject,
but the recorded results of the experiments made by the Board's
Officers will be of value, when the question of adopting a better
standard is taken up by the Board of Trade."
2. As regards purity. The gas was free from sulphuretted
hydrogen throughout the year; and the quarterly average
quantity of other sulphur compounds present in the gas was
considerably less than the quantity permitted, the maximum
not having been attained on any occasion.
Grains of sulphur per 100 cubic feet of gas; the Parliamentary
limit being 17 grains in 100 cubic feet during the months
from April to October, and 22 grains from October to April,