Concentration of acids. Historical engraving showing equipment for the concentration of acids by distillation. A glass flask (3) containing an acid solution is placed in the oven (2) and heated. As the solution heats up the water in the solution sublimes off as water vapour. The vapour rises and collects in the glass helmet (4) of the flask. As the flask is cooler than the vapour it condenses back into a liquid and runs down into the receiver vessel (5). Taken from The Laws of Art and Nature, in Knowing, Judging, Assaying, Fining, Refining and Inlarging the Bodies of Confin'd Metals (1683), John Pettus, a translation of the work by Lazarus Ercken.