It is possible to alch around 1,200 items per hour for a total of 78,000 magical experience. If the player attempts to cast an alchemy spell on a valuable item, the player will receive an alert asking if they are sure they want to alchen the item.
Automatic retaliation can be used effectively for this. Players can also cast High Alchemy by dragging and dropping an item into their wallet, provided they have the required runes. It is cast with the same speed and cooldown as if cast from the spell book or action bar.
RuneScape’s game engine runs on a unit of time colloquially referred to as “ticks”, with each tick lasting 0.6 seconds (this length of time may vary in hundredths or thousandths of a second due to things like Server lag or the number of players on a world, read here).
High level alchemy can be performed at a rate of ~1200/hour. If a Nature Rune costs 450g and the difference between the price paid and the Hochalch price is at least 1,000, you can earn 660,000+/h while gaining 78,000 Magic XP/h as F2P.