I understand they now speak Arabic because of the Muslim conquests. But prior I have read that they spoke Coptic.
I am specifically interested in verifying what the word Black means in Ancient Egyptian language. I watched a lecture about Alchemy and the authority said Egypt was what the Greek called them, but that Egypt was actually called Khemet. The name Khemet was the word used for black or dark and was likely used because of the black soil that the Nile would flood the land with.
Are there any other good sources for this?
Sure. The Oxford english dictionary for one.
Basically it was the fertile mud of the nile valley (black earth=fertile mud, as opposed to the red or white desert)
Except you don't have it quite right. Egyptians called it kēme (hieroglyphic khmi, lit. ‘black earth’, as opposed to red desert sand) (that's from wikipedia, I'm no expert on Egypt) Really old ancient (whatever, pre-classical Greek.. ask one of the Greek history experts. Anyway, "pre-ancient" Greek had it as Chēmia (Χημία), which in ancient greek took on a sort of "black magic" meaning. And then in medieval times the Latin version had the meaning as a sort of mixture (but potential still elements of the supernatural)... and really, the rest is history: Arabic: al-kīmiyā’ (الكيمياء) ‘philosopher's stone’ -> Medieval Latin: alchymia (black magic) -> Old French: alquemie, alkimie -> and finally good ol' alchemy -> chymistry (which=alchemy exactly, nothing like 'chemistry') -> and then chemistry, which is the modern science we know and love. (at least us over at the History of Alchemy Podcast do)
How and when chymistry (i.e. alchemy) turned into chemistry didn't happen over night.
Then there's archimastry, or archemy, which died out in English, but lived on in French, means (sort of) "real metallurgical alchemy" (as opposed to the spagyric or other weird spiritual stuff that came about later, but it's complicated. Basically that's a separate question if you're curious) and then eventually archimastry just meant metallurgy in French (and maybe died out in the 19th century; my French sucks). Anyway, we talk about all this stuff for hours if you're interested: http://historyofalchemy.com
Or just keep asking away, that's what I'm here for.
Edit: I forgot you sort of also asked about the etymology of the word "Egypt"... basically it comes from the city of Memphis, which the Greeks later used to refer to all of Egypt. City of Memphis: Ha(t)-ka-ptah "temple of the soul of Ptah," the creative god associated with Memphis, the ancient city of Egypt. So Ha(t)-ka-ptah -> Greek: Aigyptos
Arabic comes much later. The Arabic is Misr, which is derived from Mizraim, the name of a son of Biblical Ham. By the time they got their hands on the word "chemia" it was already referring to transmutation and the like.
Source for the etymology of Egypt is from the Online Etymological Dictionary (one of my top most used "I'm curious about that word" sort of bookmarks, in case you are like me and just wonder why we call things a certain way)