In a recent paper by Miss Chick on “The Laws of Disinfection”, it was pointed out that disinfection of bacteria is strictly analogous to a chemical reaction in which individual bacteria play the part of molecules. Thus, if n be the number of bacteria present at any time t during dis-infection, , where K is a constant. Also, if K1, K2 are these constants for two different temperatures is also constant, i.e. Arrhenius' formula for the temperature coefficient of chemical reactions holds good in the case of bacteria as well. In addition to this, it was found that the relation between the concentration of the disinfectant and the time of disinfection (that is, the time required to reduce the original number of bacteria by a given percentage) might abe approximately expressed by the empirical lawwhere C is the concentration at time t.

In recent years, values of the refractive index of liquids, and sometimes of gases, have been extensively used for determining dipole-moments. Measurements of dielectric coefficients give the sum of the orientation, electronic and atomic polarizations P 0 + P e +P a , while the electronic polarization P e can be calculated approximately from the refractive index. If the dispersion is known, P e should be given with some accuracy by calculating the refractive index at zero frequency. In order to obtain P 0 , it is necessary to know P a , a quantity which has only been determined for a few substances, the infra-red spectrum of which has been examined in detail. It is, however, often assumed that P a is negligible or, at least, small in comparison with P e . In some cases, an approximation on an empirical basis has been made by assuming that P a is proportional to P e , or that P a + P e is equal to the value of P e when calculated from the refractive index for the yellow sodium line. Such assumptions can hardly be regarded as satisfactory. In liquids, determination of the polarization is complicated by the necessity of employing a solvent, but, with gases, no such difficulty exists. P a can therefore be determined with some accuracy by measuring the refraction for different wave-lengths, and the dielectric coefficient at different temperatures. Numerous measurements of the refractive index of the commoner gases have been made, but the results of different observers are not always in agreement and frequently the dispersion has not been determined. The dielectric coefficient of the same sample of gas seems never to have been measured.

In Part I* measurements of the dielectric coefficients of hydrogen and the rare gases a t two temperatures were recorded. The investigation has now been extended to a number of other gases with a view to determining the electric moment of their molecules and comparing the values of the dielectric coefficient with those of the refractive index at long wave-lengths. The results now given are those of a series of measurements dating from 1928, and during their progress several papers comprising the same subject have been published. These will be discussed later and the results compared.When dealing with all but the simplest gases a knowledge of the compres sibility is essential in order to reduce the values of the dielectric coefficient at different temperatures to those for equal density; it is also desirable to employ gases which have been purified with the greatest care. The com pressibilities of the gases under reference have been determined approximately by measuring the dielectric coefficients a t different pressures as for ammoniaf and several values have been confirmed by direct determination or by refractometric measurements, an account of which will be given elsewhere.Determinations have been made by the " series " method previously employed and also by the " parallel ", method using a condenser specially constructed for measuring very small capacity changes. The results given by the two methods are in satisfactory agreement. The following gases have been examined : methane, ethane, propane, ethylene, propylene, acetylene, silicane, silicoethane, carbon monoxide and dioxide, oxygen, nitrogen, air, nitrous oxide, nitric oxide, silicon tetrafluoride and sulphur hexafluoride. Of these only propylene, carbon monoxide and the two oxides of nitrogen have a measurable electric moment.

No abstract

No abstract