view of studying the mean free path of these ions and the amount of energy lost per collision similarly as has been determined for electrons and atoms.13 The results show a much larger, by some folds, mean free path than one would calculate.

Williams and HuxfordI4 also determined the elementary charge by means of K+ instead of on electrons and find an agreement within experimental error.

The effect of bombarding or exciting salts as lithium chloride by K+ ions has been studied by Badareu."

The foregoing discussion has clearly brought out the fact that ions such as those of the dkali metals Na, K, and Cs, are in general relatively less effective than electrons in bringing about chemical and physical changes. Further experiments should give more information on the r8le played by charged particles in excitation and chemical reaction.

Summary

1. Attention was called to the complicated electrical phenomena in the arc and the desirability of dissecting i t wherever possible so as to obtain definite results from the various parts. These results can then be applied to the study of the chemical reactions taking place in the arc.

2. The description of apparatus containing a new source of positive ions was described in comparison to the equivalent electron source.

3. Physical and chemical experiments were described in which similar results were sought with electrons and with positive ions and under the same conditions as:

(a) The activation of N2 + 3Hz mixture in the synthesis of ammonia. (b) Determination of q the work function for charged particles from hot

surfaces. (c) Bombardment of metal surfaces. (d) Scattering of charged particles from surfaces. ( e ) Excitation and ionization of gases and vapors. (f) Behavior of gases toward the passage of ions through them. (g) Determination of the unit electric charge of a positive ion.

IWDurbi Phvs. Rev.. 30, 844 (1927); Kenard, Ibid., 31, 423 (1928); Hamwell, Ihif . , 31, 634 (1928).

"Williams and Huxford, Ibid., 31, 1120 (1928) ' 5 Badareu, Phyn'k. Zeit., 27, 634 (1926).

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