On the Igniting Point of Petroleum. 343 
four seconds. It will be noticed that differences of igniting- 
point in any one specimen are obtained varying trom ten to 
thirty degrees. The other causes of variation already 
alluded to were excluded by the experiments being all per- 
formed by one operator of experience, each set of experi- 
ments being made under equal conditions, and each 
experiment occupying the same amount of time,—about 
three minutes. The table will also serve to show that the 
Lancet showed (March 29, 1862) in regard to mineral oils 
sold in London, and what the observations of O’Neill 
showed at Manchester in June, 1862 (Chemical News vol. v., 
p- 312), and of Tate at Liverpool, in September 13862, 
(Pharmaceutical Fournal, vol. iv., New Series, p. 150),namely, 
that much of the petroleum supplied to the public is dan- 
gerous. In addition it shows that, as much of it (in the 
words of the Act) “gives off an inflammable vapour at a tem- 
perature of less than one hundred degrees of Fahrenheit’s 
thermometer,’ the law has not yet had the effect anticipated 
namely, the exclusion from retail trade of that quality of 
petroleum which is so badly refined asto have dangerous, 
because unsuspected, properties. 
And now, with regard to a method of taking the ignit- 
ing-point of petroleum-vapour, which shall be reliable and 
constant in the results of its application. 
As petroleum is not a definite chemical compound, ‘but 
a varying mixture of several hydrocarbons ; as, in short, it 
has no constant chemical or physical property of which 
adyantage might be taken in devising a ready method of 
taking igniting-points, it follows that the method selected 
must be more or less arbitrary, empirical, conventional. It 
is true, that their volatility is a constant physical property, 
and MM. Salleron and Urbain in France, have, it is said, 
contrived an apparatus for taking the tension of the vapour 
of mineral oils, which is obviously proportional to their 
volatility ; adopting 64 millimetres of water at, apparently, 
35° C. as the limit of safety; but only an abstract of their 
paper was published, in the Comptes Rendus of January 
2, 1866; their full paper does not seem to have been 
printed, so that I am unable to judge of the merits of the 
method. It has not the recommendation of being a direct 
process. The only feasible plan would seem to be, select a 
direct method, simple in principle, easy of execution, occu- 
pying little time in performance, and inexpensive; and 
when this is found, to take steps for accomplishing a far 
more difficult task, namely, securing its universal adoption. 
NEW SERIES.—VOL. I. FF 
