Preparation of Dusts for Animal Experiments

It is clear that the surface properties of substances, which in the form of particulate matter cause lung injuries play an exceedingly important role in the development of the lesions. Thus the preparation of the material to be tested must not alter the physicochemical properties at the interface of the material with its environment before getting in contact with cells and tissues. 

It is important to distinguish between true dissolution of quartz involving the production of molec-ularly dispersed silicic acid and the production of mosaic silica (Richardson and Waddams 1955). The latter is not a case of true dissolution but a separation of fragments of crystalline siUca which forms a separate phase. 

The effect of potassium permanganate on dissolution gave inconclusive results (Waddams 1958). 

This was thought to result from interaction between hydrated manganese dioxide formed when the anionic vacancies were oxidised and either the centres at which dissolution occurs or the silicic acid formed. Using HjOj as oxidant considerably enhanced 48 h solubility values. When the volume of air in the tubes used for solubility tests was varied from 0 to 50 times the volume of extractant, the effects of 48 h solubility values increased noticeable over the range covered. Welch (1955) has commented on the ability of oxidising and reducing atmospheres to modify the reactivity of solids by changing the concentrations of lattice defects. Thusfar, however, no such simple room-temperature effects as those described here have been reported. 

There is thus reason to believe that vacancies in the quartz lattice play an important role in the following processes  

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