What type of reaction occurs in the formation of Arsenic Sulphide colloidal solution?

Dear Student

​​​​​​Double decomposition reaction occurs.
An Arsenic sulphide Sol is prepared by passing a slow stream of hydrogen sulphide gas through a cold solution of arsenious oxide. This is continued till the yellow colour of sol attains maximum intensity.
As₂​O₃​ + 3 H₂​S → As_2​S₃​​ + 3 H₂​O
Excess hydrogen sulphide is removed by passing in a stream of hydrogen.

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