The ancient Jews prepared what they called Borith (translated “soap” in Jeremiah, ii, 22, and Malachi, iii, 2) by filtering water through vegetable ashes. Borith was therefore an impure carbonate of potash. It is probable that the salt-wort was generally employed for this purpose, and some of the old versions of the Old Testament give the herb “Borith” as the proper sense of the passages referred to above. In any case the alkaline solution produced from vegetable ashes was used for bleaching and cleansing purposes. The Roman “lixivium” was similarly prepared, and the process is still followed in some countries where there are dense forests. The Arabic word “al-kali” was apparently applied to the product from the word “qaly,” which meant “to roast.” The earliest known use of the term is, however, found in the works of Albertus Magnus, early in the thirteenth century. A process of making caustic potash by filtering water through vegetable ashes with quicklime is described in the works attributed to Geber, but this is in a treatise now known to have been written in the thirteenth or fourteenth century. It was only in 1736 that the three alkalies, soda, potash, and ammonia, were definitely distinguished by Duhamel as mineral, vegetable, and animal or volatile alkalies. A formula for a solution of caustic potash was given in the P.L., 1746, under the title of Lixivium Saponarium. Equal parts of Russian potashes and quicklime were mixed, wetted until the lime was slaked, water afterwards added freely, and after agitation the solution poured off. This was ten years before Black’s classic investigation already referred to. Before Black, and for some time afterwards, there were several theories in explanation of the action of the lime on the potashes. The lime had been tamed, but the potash had become more virulent. One popular suggestion was that the lime had withdrawn a kind of mucilage from the potashes; another that it had the effect of developing the power of the potashes by a mechanical process of comminution. A German chemist named Meyer, who vigorously opposed Black’s conclusions, maintained that the lime contained a certain Acidum Causticum or Acidum Pingue, which potashes extracted from it. In the P.L., 1788, the process was altered by increasing the proportion of the lime, and the product was described as Aqua Kali Puri. Subsequently the proportion of the lime employed was reduced.