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A mass-spectrograph analysis has been made of the ions formed by electron impact in Na, K, Rb, Cs vapors and in Kr and Xe. The electron energy varied from zero to 700 electron-volts. Multiply charged ions were formed in all cases when the electron energy was sufficiently high. The ionization potentials for the various ions are given in the table. In general the curves showing likelihood of formation of these ions as a function of electron energy are of the usual shape. In the cases of ${\mathrm{K}}^{+}$, ${\mathrm{Rb}}^{+}$, ${\mathrm{Cs}}^{+}$ and ${\mathrm{Cs}}^{2+}$ there are evidences of additional mechanisms of formation which appear at the following potentials: for ${\mathrm{K}}^{+}$ at 15.5 and 150 volts; for ${\mathrm{Rb}}^{+}$ at 12.5 volts; for ${\mathrm{Cs}}^{+}$ at 10; 17.5, and 60 volts; for ${\mathrm{Cs}}^{2+}$ at 80 volts.

Four models of the organization of feature-testing units in the perception of phonemes are developed and tested against data drawn from a number of published studies. The independence model, which asserts that features are tested independently of each other, is conclusively rejected. The response-conditional and stimulus-conditional models require individual feature-testing units to be dependent, respectively, on the responses of other feature-testing units and on the other features present in the stimulus. Both these models handle perceptual confusions very well among stop and nasal consonants, but are less satisfactory for fricatives. Finally, the correct-conditional model requires individual feature-testing units to be dependent on the correctness of the decisions made by other feature-testing units; this model is very poor for perceptual confusions but quite good for mnemonic confusions. In addition, some of the distinctive features currently favoured by linguists are shown to provide unsatisfactory descriptions. The implications of this study are that perceptual and mnemonic processes are different in certain basic respects, and that many current scaling models are ignoring important types of structure in the data they analyse.