========================================================================= | Temperatures Oxidizer +----------+---------+---------+--------+---------- | 0-2° | 20° | 50° | 75° | 98-100° ----------------------+----------+---------+---------+--------+---------- Turnip juice | Faint | Good | Good | | Negative. 1 per cent. | | | | | blood extract | Faint | Fair | Good | | Fair. M/20 K_{4}Fe(CN)_{6} | Negative | Good | Bright | Bright | Good. M/100 KMnO_{4} | Fair | Good | Bright | Bright | Faint | | | | | flash. M/50 K_{2}Cr_{2}O_{7} | Negative | Fair | Faint | Fair | Negative. M/100 CrO_{3} | Negative | Good | Bright | Bright | Faint. M/10 KCr alum | Negative | Faint | Faint | Faint | Negative. M/10 NH_{4}Fe alum | Negative | Faint | Faint | Faint | Very | | | | | faint. MnO_{2} | Negative | Fair | Fair | Fair | Negative. NaClO | Bright | Bright | Bright | | Fair | flash | flash | flash | | flash. ----------------------+----------+---------+---------+--------+---------- Quite a number of instances are known in which increasing the mass of reacting substances leads not to an increase but to an actual cessation of luminescence. This fact does not confirm the theory that reaction velocity is a determining factor in luminescence. The conditions for the luminescence of white phosphorus are most interesting and unusual. (See van't Hoff, 1895; Ewan, 1895; Centnerszwer, 1895; Russell,1903; Scharff, 1908.) Phosphorus will only begin to luminesce at a certain small pressure of oxygen. This "minimum luminescence pressure" of oxygen is very low, so low that earlier observers, failing to remove traces of oxygen, thought that luminescence might occur in absence of oxygen. Curiously enough there is also a "maximum luminescence pressure" of oxygen above which no luminescence occurs. Phosphorus will not luminesce in pure oxygen. Between the minimum and maximum is an "optimum luminescence pressure" where luminescence of the phosphorus is brightest. The exact values of these pressures vary with degree of water vapor present and with temperature. According to Abegg's _Handbuch der anorganischen Chemie_, the maximum luminescence pressure with water vapor present, is 320 mm. Hg at 0° and increases 13.19 mm. Hg for each degree rise in temperature. This means that for a definite temperature, say, 20°, phosphorus will not luminesce with an oxygen pressure of 583 mm. Hg, but will luminesce with pressures under this. If, however, we