Abstract: A photoacoustic gas analyzer comprising a measuring chamber, a modulated light source, and at least one microphone in connection with the measuring chamber and measuring the changes of pressure caused by the absorption of the light in the chamber. The measuring chamber comprises an inner surface with a reflecting coating. The measuring signal is thereby proportional to the gas concentration and is not provided as the difference between two almost equal values. As a result it is possible to measure small gas concentrations provided the light intensity within the measuring chamber suffices.

Abstract: Fat in a fat-containing sample, in particular a milk sample, is determined quantitatively by infrared absorption technique, using as sample waveband a band characteristic to carbon-hydrogen bonds, instead of the conventional triglyceride carbonyl band. This avoids the dependency of the measured result on the fat composition of the sample. Influences from other components in the sample are compensated for. A preferred method uses double wavelength determination, with sample wavelength in the interval from 3.475 to 3.51 .mu.m and reference wavelength in the range between 3.51 and 3.60 .mu.m.

Abstract: An apparatus for measuring components of liquid samples, such as milk samples, based on the ability of these components to absorb infrared radiation at certain frequencies. A single radiation beam is directed through a cuvette containing the sample, and the apparatus comprises a plurality of pairs of optical filters. Each of these pairs is associated with a respective one of the components to be measured and comprises a component filter for passing infrared radiation at a narrow frequency band at which the radiation absorbing ability of the said component is relatively high, and a reference filter for passing infrared radiation at a different narrow frequency band at which the radiation absorbing ability of the component is lower.