xozhang3: Very curious! I definitely missed that quotation!
I didn't have much success in separating out 'colloidal gold sulphide' from 'colloidal gold' in my searches.
If you believe Wikipedia [
], "Gold sulfide is the inorganic compound with the formula Au2S. It is the principal sulfides of gold. It decomposes to gold metal and elemental sulfur, illustrating the 'nobility' of gold."
This leads me to wonder why anyone would use gold sulphide as a colloid and not plain old gold, allowing for gold sulphide to decompose into its primary components!
Of course, I am getting lost in this whole issue as I am the farthest from a chemist to have the proper understanding!