On the Production of Light by Chemical Action. 161 
the prism must of course be set vertically. The former mode 
possesses great advantages, as will be presently pointed out. + It 
is to be understood, in all cases, that the eye-piece of the tele- 
scope is adjusted to give a sharp image of the shit, and the prism 
is at its angle of minimum deviation. 
By this arrangement I have examined a great number of dif- 
ferent flames, as those of oil, alcohol, solutions of boracie acid 
and nitrate of strontian in alcohol, phosphorus, sulphur, earbonie 
oxyd, hydrogen, cyanogen, arseniuretted hydrogen, &c. Among 
these it will be noticed different colors oceur; oil gives a yellow 
flame, alcohol a pale blue, boracic acid green, strontian red, phos- 
phorus yellowish white, sulphur and carbonic oxyd blue, hydro- 
gen pale yellow, cyanogen lilac, arseniuretted hydrogen white, &c. 
Notwithstanding this diversity of color, all these flames, as 
well as many others I have tried, yielded the same result. E’very 
prismatic color is found in them. Even in those cases where 
_ the flame is very faint, as in alcohol and hydrogen gas, not only 
