In the old potash-making process: Wood ashes after lixiviation and evaporation; impure potassium hydrate. Hence Black-salter, one who makes black salts.
1880. ‘E. Kirke,’ Garfield, 6/2. Our future President became prime-minister to a black-salter.
1881. W. M. Thayer, Log-Cabin to White Ho., x. Potash … in its crude state, was called ‘black-salts.’ The manufacturer of the article was called a ‘black-salter.’
