I'm not a chemist but I'm about to order some ferric chloride so your question made me curious. A quick google search shows that it may be Ammonium persulfate (APS) which is used as an alternative to ferric chloride. I've pasted in some info I took directly from Wikipedia:

Ammonium persulfate (APS) is the inorganic compound with the formula (NH4)2S2O8. It is a colourless (white) salt that is highly soluble in water, much more so than the related potassium salt. It is a strong oxidizing agent that is used in polymer chemistry, as an etchant, and as a cleaning and bleaching agent. Illustrative of its powerful oxidizing properties, it is used to etch copper on printed circuit boards as an alternative to ferric chloride solution.[4] This property was discovered many years ago. In 1908, John William Turrentine used a dilute ammonium persulfate solution to etch copper. Turrentine weighed copper spirals before placing the copper spirals into the ammonium persulfate solution for an hour. After an hour, the spirals were weighed again and the amount of copper dissolved by ammonium persulfate was recorded. This experiment was extended to other metals such as nickel, cadmium, and iron, all of which yielded similar results.

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I'm not a chemist but I'm about to order some ferric chloride so your question made me curious. A quick google search shows that it may be Ammonium persulfate (APS) which is used as an alternative to ferric chloride. I've pasted in some info I took directly from Wikipedia:

Ammonium persulfate (APS) is the inorganic compound with the formula (NH4)2S2O8. It is a colourless (white) salt that is highly soluble in water, much more so than the related potassium salt. It is a strong oxidizing agent that is used in polymer chemistry, as an etchant, and as a cleaning and bleaching agent. Illustrative of its powerful oxidizing properties, it is used to etch copper on printed circuit boards as an alternative to ferric chloride solution.[4] This property was discovered many years ago. In 1908, John William Turrentine used a dilute ammonium persulfate solution to etch copper. Turrentine weighed copper spirals before placing the copper spirals into the ammonium persulfate solution for an hour. After an hour, the spirals were weighed again and the amount of copper dissolved by ammonium persulfate was recorded. This experiment was extended to other metals such as nickel, cadmium, and iron, all of which yielded similar results.

Thanks, Matt. I appreciate you taking the time to reply. I'm not sure what I will use it for yet, possibly for removing scale.