Note 6 — CLASS I. SALTS.
William Withering translation
As the tincture of heliotropium is the niceſt known teſt of the preſence of an acid, it may not be amiſs to mention that it may be had from dyers under the name of litmus. It is very cheap, and generally requires to be greatly diluted with diſtilled water before it can be uſed. W.