1. Diffusion dispensers can be used in producing testing instruments for obtaining given vapor concentrations in air. It is advantageous to use a dispenser with a porous membrane, thus making it possible to cover the entire range of concentrations required for testing working instruments. In order to produce an instrument with a very wide range of concentrations it is sufficient to have two elements with a porous membrane mounted in parallel and connected separately as required. 2. All the dispensers possess a range of carrier-gas filtering speeds for which they have a well defined linear characteristic with the vapor concentrations in the mixture being inversely proportional to the carrier gas filtering speed. 3. For dispensing purposes only pure liquids should be used which do not change their composition in evaporating, i.e., which have a constant saturated vapor pressure at a constant temperature. 4. In order to obtain the required concentrations of complex liquids (benzene, kerosene, etc.), individual carbohydrates should be used with properties correspnding to the mean properties of the above complex compounds. 5. It is not advantageous to use a pure computation method for determining the composition of test mixtures. It is advisable to determine experimentally the constant of instruments during their certification. However, in developing an instrument it is desirable to establish its reliability according to theoretical computations.