The word "purifyings" is spelled with a y instead of an i because of the pronunciation of the word. In IPA phonetic transcription, the spelling appears as /ˈpjʊərɪfaɪɪŋz/. The y sound represents the /j/ sound that is heard at the beginning of the second syllable. This is called a palatal glide, which occurs when the tongue moves from a consonant sound (r) to a vowel sound (i). The double i at the end represents the long vowel sound /aɪ/ in the word.
The word "purifying" is derived from the verb "purify", which comes from the Old French word "purifier" and the Latin word "purificare". In Latin, "purus" means "pure" and "facere" means "to make". Therefore, "purificare" means "to make pure". This verb was then adapted into "purify" in Middle English, and from there "purifying" was derived as the present participle.