ture, luminescence will occur with an oxygen pressure of 583 mm. Hg.
A somewhat analogous case is presented by the oxidation of pyrogallol solution in contact with ozone, except that in this reaction too high a concentration of pyrogallol will hinder the oxidation. I have not studied the effect of varying concentrations of ozone. If oxygen, passed through an ozonizer (the silent electric discharge tube), is bubbled through m/100 pyrogallol, no luminescence occurs at 0°, a fair luminescence at 20°, a good luminescence at 50°, and a bright luminescence at the boiling point. If the pyrogallol is of m concentration, no luminescence occurs at 0° or 20°, a fair luminescence at 50°, and a bright luminescence at the boiling point. For a definite temperature, say 20°, no light appears if the pyrogallol is of m concentration, but if we raise the temperature, luminescence can occur. The similarity to phosphorus is obvious. Thus the "maximum luminescence pressure" of pyrogallol increases with increase of temperature.
We have already seen that pyrogallol can also be oxidized, if H2O2 is present, by a great variety of substances, such as peroxidases of potato or turnip juice, hæmoglobin, KMnO4, K4Fe(CN)6, CrO3, MnO2, hypochlorites and hypobromites, or colloidal Pt and Ag. For convenience we may collectively speak of these as oxidizers. They are recorded in [Table 13]. No light occurs if H2O2is absent. In the case of some of these oxidizers pyrogallol will luminesce in dilute concentrations but not in strong. Also, dilute pyrogallol will luminesce with a dilute solution of oxidizer but not with a concentrated solution of oxidizer. The effect of rise in temperature in these cases also is to increase the "maximum luminescence concen
tration" of pyrogallol and the "maximum luminescence concentration" of oxidizer. [Table 11] shows this effect of temperature with K4Fe(CN)6 and varying concentrations of pyrogallol, and [Table 12] shows the effect of temperature with pyrogallol and varying concentrations of K4Fe(CN)6. [Table 10] shows the relation between temperature and intensity of luminescence with pyrogallol and various oxidizers. The terms faint, fair, good, and bright are purely relative designations of brightness as estimated by the eye, for accurate measurements of weak intensities are very difficult to make.
From [Table 10] it should be noted that the intensity of luminescence of pyrogallol oxidized with most oxidizers is actually less at the boiling point, a fact which I have repeatedly verified. Let us now see how these facts are to be explained. If we assume that luminescence is dependent on reaction velocity, the intensity of luminescence should increase with increasing temperature. Up to a certain limit this is what we find, but at temperatures above this limit the intensity of luminescence actually decreases. The duration of luminescence also decreases. There is an optimum temperature for luminescence in many cases and we can only conclude that luminescence depends not on a very rapid reaction velocity but on a certain definite reaction velocity. Assuming that this is true, how can we account for the anomalous fact that in high concentrations of oxygen, phosphorus will not luminesce or that in high concentrations of pyrogallol, there is no luminescence in presence of ozone or of oxidizer and H2O2. Of course with high active mass of oxygen (in case of phosphorous luminescence) or of pyrogallol (in case of pyrogallol luminescence) the reaction velocity must be
greater than the optimum. If that is the case, then lowering the temperature should reduce the reaction velocity to the optimum and light should appear. However, as we have seen, not lowering but raising the temperature causes luminescence with high oxygen concentration or high pyrogallol concentration.
TABLE 11
Temperature, Concentration of Pyrogallol, and Light Production. An Equal Amount of m/20 K4Fe(CN)6 is Mixed with Pyrogallol + 3 per Cent H2O2
| Concentration of pyrogallol (after mixing) | Temperatures | ||||||
|---|---|---|---|---|---|---|---|
| 0-2° | 10° | 20° | 30° | 50° | 75° | 98-100° | |
| m/4 | Negative | Negative | Good | Very faint | Faint | Fair | Faint |
| m/40 | Negative | Faint | Faint | Faint | Good | Bright | Good |
| m/400 | Faint | Fair | Good | Good | Good | Bright | Bright flash |
| m/4,000 | Bright | Bright | Bright | Bright | Bright flash | Fair flash | Negative |
TABLE 12
Temperature, Concentration of Ferrocyanide and Light Production. An Equal Amount of K4Fe(CN)6 is Mixed with m/100 Pyrogallol + 3 Per Cent H2O2