Tyndall spectra

A brief treatment of scattering by large, absorbing particles and the concept of absorption and scattering cross sections are presented in Section 5.7 along with two examples of applications of the Mie theory (to absorbing, but small, particles) and a discussion of Tyndall spectra. 

Vonnegut and Neubauer (24E), using liquids of low conductivity, have produced two types of droplet distributions by means of high voltage 5000 volts direct current produces a uniform stream of droplets of 100 micron diameter at the rate of about 100 per second. A cloud of fine particles which are so uniform in size that Tyndall spectra are apparent, is also produced. 

The ability of diffraction techniques to determine size is in most cases a direct function of the degree of monodispersity of the suspension being tested. Several alternative techniques are available, dependent on the size of the particles. Some suspensions exhibit higher order Tyndall spectra for incident white light. Size determination is then easily made. 

For Rayleigh scattering / = 0 at 90°. As R increases, theory shows that X is a periodic function of diameter for monosize particles, and this has been used to measure particle size [78] specifically the size of aerosols in the size range 0.1 to 0.4 pm [79]. It has also been used to determine the sizes of sulfur solutions [80] In this work, transmission and polarization methods yielded results in accord with high order Tyndall spectra (HOTS) for sizes in the range 0.365 to 0.62 pm. In the limited region where (0.45[Pg.537]

Pierce, PE. and Maron, S.H., Prediction of minima and maxima in intensities of scattered light and of higher order tyndall spectra, J. Colloid Set, 19, 658-672, 1964. 

To obtain a monodispersed sol it is necessary to add the water to the organic sulfur solution and not the other way round. The observed particle size, derived from higher order Tyndall spectra, ranges from 0.20 to 0.45 jum if the initial sulfur concentration in ethanol is between 0.25 and 2.9 mg 1 [8]. 

Od n has shown that Raffo sols can be separated into fractions of differing particle size by fractional precipitation with increasing concentrations of NaCl. As larger the particles as less NaCl is needed for precipitation [38]. Under special conditions monodispersed Raffo sols of particle size between 0.1 and 1.0 can be prepared directly from very dilute aqueous thiosulfate and sulfuric acid or hydrochloric acid without fractionation. These sols are characterized by higher order Tyndall spectra [39]. 

Autoxidation of aqueous H2S solutions results in elemental sulfur, sulfite, thiosulfate, and eventually sulfate. However, under certain conditions monodispersed sulfur sols with particle diameters of between 0.2 and 1.2 /um are obtained [48]. For example, a solution of H2S of concentration 46 mmol 1 in pure H2O exposed to air at 25 °C became turbid after an induction period of ca. 8 h and then showed briUiant higher-order Tyndall spectra. A solution saturated in H2S exhibited a pH value of 4.1 and was rapidly oxidized in an atmosphere of pure O2. At pH values >8 no elemental sulfur was formed (clear colorless solution), in the range pH=7-8 yellow solutions were obtained (polysulfide anions), while at pH<7 turbid solutions were produced but the induction period was as longer as lower the pH value [48] ... 

Lamer VK (1948) Monodisperse colloids and higher-order Tyndall spectra. J Phys Colloid Chem 52 65-76... 

---