Ionization efficiency curves near threshold have been measured with a mass spectrometer employing a monoenergetic eletron beam. The ion source, which is used for the experiment, is a modified Nier type. The electron gun assembly can be removed as the unit from the ionization chamber and easily cleaned. Ionization efficiency curves for xenon, n-butane and iso-butane are given.

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The mass spectra of six monocyclic γ-pyrones are recorded (Fig. 1-6), and their fragmentation reactions are described. The characteristic features of the fragmentation pattern are: i) the elimination of carbon monoxide from the molecular ion, and ii) the retro-Diels-Alder cleavage of the γ-pyrone ring.
As a pertinent example, the fragmentations of 2, 6-dimethyl-γ-pyrone (II) are discussed in detail, where the meta-stable ion peaks (m*) for most reaction steps were clearly observed (Scheme I and II) .
The primary process of the fragmentation of II is an expulsion of carbon monoxide from the molecular ion A (m/e 124) with generation of a corresponding furan ion B (m/e 96) (Reaction 1) . The subsequent loss of a hydrogen atom from B would give an oxonium ion C (m/e 95) (Reaction 2) . A skeletal rearrangement of the furan ion B may afford an equivalent ion B' (m/e 96) (Reaction 3), which leads to ions of D (m/e 43) and E (m/e 81) through plausible mechanisms (Reaction 4 and 5) . The loss of carbon monoxide from E yields methylcyclopropenyl cation F (m/e 53) (Reaction 6) . The intermediacy of the furan ion in the fragmentation is supported by the similarity of the spectrum of 2, 6-dimethyl-γ-pyrone(II)to that of 2, 5-dimethyl-furan.
Another important fragmentation pathway of II is the retro-Diels-Alder cleavage of the γ-pyrone ring with formation of an ion G (m/e 84) (Reaction 7) . A further loss of a methyl radical from G produces an ion H (m/e 69) (Reaction 8) .
Several minor modifications and some additional fragmentation processes are required to interprete the spectra of other γ-pyrones. For methoxyl derivatives (IV and V), the expulsion of carbon monoxide from the molecular ion is followed by the loss of a methyl radical from the methoxyl group to give an oxonium ion, from which carbon monoxide is further eliminated (Scheme III) . When 2 and 6 positions of γ-pyrones are not substituted as in I and III, the hydrogen migration takes place after the retro-Diels-Alder cleavage of the ring, and carbon monoxide expulsion from the resulting ion gives the corresponding ketene radical cation (Scheme IV) . In the case of bromo derivative VI, the fragmentation involves also the expulsion of bromine radical(Scheme V).
γ-Pyrones are isoelectronic with α-pyrones and tropones, and their mass spectral behaviors are expected to be similar in general. Comparisons of their spectra, however, indicate slight differences, which are well accounted for by the mechanistic scheme discussed above.

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The gaseous products from a power transformer under overloading were analyzed by means of a mass spectrometer. Substantial amounts of hydrogen, carbon dioxide and lower hydrocarbons were detected in the gas formed from the overloaded transformer, while no detectable amount of these compounds were found in the case of normal condition. These results suggest that the mass spectrometric analysis of the transformer gas is a convenient method for checking up the operating condition of the power transformer.

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The gaseous and volatile products formed by the pyrolyses of polyacrylonitril and polyvinylidene chloride in a vessel under existence of the calibrated amount of air at various temperatures were analysed quantatively by means of a mass spectrometer. As the result, the main components of the gaseous and volatile products formed from polyacrylonitril and polyvinylidene chloride were identified. Similar experiments were also carried out on the synthetic fablics, and the main components of the gaseous and volatile products formed by pyrolyses were identified.

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Mass spectrometric quantitative analysis on the gaseous and volatile products formed by yrolysis of polyvinyl alcohol and polyvinyl chloride in a vessel containing the calibrated amounts of air at various temperatures was studied. The pyrolytic products were hydrogen, carbon monoxide, carbon dioxide, lower hydrocarbons and others. Similar experiments were also carried out for the synthetic fibers, and the main components of the gaseous and volatile products formed by pyrolysis were identified. No marked difference in the composition and amounts of the gaseous and volatile products at each pyrolytic temperature between polyvinyl chloride and polyvinyl chloride fiber was observed.

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