Stannic chloride $\mathrm{(SnCl4)}$ is hygroscopic and forms crystalline hydrates containing $3,5,6$, and $8$ molecules of water of crystallization. The pentahydrate $\mathrm{SnCl} 4.5 \mathrm{H} 2 \mathrm{O}$, is known as "butter of tin" or "oxymuriate of tin." It is used as a mordant for dyes.
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