Electron diffraction and proton magnetic resonance techniques were used to study the dehydration of tin( IT-) hydroxide to cassiterite. Therniogravi~netric curves exhibited points of inflection which are attributed to definite crystalline compounds because the corresponding polvders produced sharp electron diffraction lines. Formulas based on chemical analysis are proposed for the dehydration stages, as is a possible, over-all dehydration mechanism. The various dehydration stages were studied by observing the temperature dependence from 80 to 300'K of their broad proton magnetic resonance line shapes. Analysis of the line shape for the first dehydration stage Sn03H2, at 80"K, indicates that the protons occur in OH groups arranged such that three or more protons are clustered together. The analysis is complicated by some motional narrowing of the absorption line, which persists at 80'K. The temperature range over which the line shape broadens is large, suggesting that more than one type of motion is involved. Motional narrowing does not appear to be present a t 80'K in the second dehydration stage, Sn20jH2, but the absorption line is much narrower and indicates that the protons occur in isolated OH groups. The proton magnetic resonance was too weak in the third and fourth dehydration stages to provide useful data.

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