A NEW METHOD FOR ANALYZING GAS MIXTURES

The analysis of gas mixtures is of great importance both for various branches of production and from the standpoint of labor protection and safety engineering. Existing methods are distinguished by excessive slowness. Their slowness and difficulty increase rapidly as the number of components in the mixture grows.

The listed shortcomings are absent from a new method of analysis developed by M. L. Veingerov at the State Optical Institute. Veingerov’s method is based on a phenomenon discovered simultaneously in the middle of the last century by Bell, Tyndall, and Röntgen. These authors found that in certain gases, under the action of very intense irradiation by the interrupted radiation of an incandescent body, sound oscillations arise with a frequency equal to the interruption frequency. The cause of this effect is absorption within the gas volume of quanta corresponding to the molecules’ own infrared frequencies. This absorption under interrupted irradiation leads to interrupted heating of the gas, creating pressure pulses. Until now this phenomenon had found no practical application.

M. L. Veingerov used this effect in a very simple and ingenious instrument, whose construction and operation are explained by Fig. 1, where \(L\) is the light source (a small incandescent lamp), \(D\) is a perforated disk for producing an interrupted light flux, \(K\) is a sealed chamber containing the mixture being studied, \(M\) is a microphone of one or another device that receives the oscillations that arise and transmits them to amplifier \(A\), which sends the amplified and detected pulses to an ordinary pointer galvanometer \(G\). A very substantial innovation in this instrument, compared with the installations of Bell and others, is that the frequency of interruption of the light by disk \(D\) is made equal to the natural frequency of chamber \(K\). This tuning to resonance increases the sensitivity of the instrument by approximately 1000 times, which is exceptionally important in practice.

Since gases having molecules of the type \(H_2\) cannot absorb in the infrared region1, in the case when, for example, air free of impurities is enclosed in the chamber \(K\), the galvanometer \(G\), despite the presence of intermittent illumination, gives no deflection. But if a gas (vapor) with molecules absorbing in the infrared region—such as, for example, vapors of water, benzine, CO, etc.—is admixed with the air, the galvanometer immediately detects a current.

Fig. 1. Diagram of Veingerov’s instrument

In this form, Veingerov’s instrument obviously still cannot serve for the purposes of mixture analysis—it is merely an indicator of the presence of a more or less significant quantity of one or another impurity, or of several impurities simultaneously. But since each of the impurities has absorption frequencies characteristic of it alone, by adding to the described device test cuvettes containing, in pure form, each of the possible impurities at a sufficiently high concentration, it becomes easy to carry out the analysis of mixtures as well. A test cuvette (shown in Fig. 1 by a dotted line) is placed in the path of the beam between \(D\) and \(K\) and absorbs the frequencies characteristic of the corresponding substance. As a result, the galvanometer reading decreases (if other absorbing impurities are also present in the air) or else the current falls to zero (if there is no impurity and the given frequency is completely absorbed in the test cuvette). The same method is used to detect other impurities, and the degree of decrease in the galvanometer reading makes it possible to judge their concentration.

Thus this instrument makes it possible to carry out express analysis of gas mixtures. In addition, it has another advantage: it permits continuous observations of changes in impurity concentrations. For this it is sufficient to pass a continuous stream of the gas under investigation through the chamber \(K\) via the tubes \(T_1\) and \(T_2\). All this suggests that this new and entirely original Soviet instrument will find broad applications. In addition to the fields mentioned above, it can be used successfully at meteorological stations, for example, for continuous observations of air humidity.

N. Khlebnikov, Moscow

Literature

1. K. Schaefer and F. Matossi, Infrared Spectra, ONTI, 1935, p. 138.

1. Reference as indicated in the source text. ↩