Soap (בֹּרַית, borith; Sept. πόα) occurs in Jer 2:22, "For though thou wash thee with nitre, and take thee much soap, yet thine iniquity is marked before me, saith the Lord God;" and again in Mal 3:2, "But who may abide the day of his coming? and who shall stand when he appeareth? for he is like a refiner's fire, and like fullers' soap." From neither of these passages does it distinctly appear whether the substance referred to by the name of borith was obtained from the mineral or from the vegetable kingdom; but it is evident that it was possessed of cleansing properties, and this is confirmed by the origin and signification of the word, which is thus illustrated by Celsius: "A verbo ברר, barar, purificavit, quae vox etiam apud Chaldaeos, Syros, Arabes, in usu fuit, descendit nomen בר, bor, puritas" (Hierobot. 1, 449). So Maimonides, on the Talmud tract Shemittah, "Species ablutionibus aptae, uti sunt borith et ahal." In fact, the simple בֹּר, bor, itself denotes a vegetable alkali used for washing (Job 9:30) and as a flux for metals (Isa 1:25). SEE ALKALI.
The word borith is very similar to the boruk of the Arabs, written baurakh in the Latin translations of Serapion and Avicenna, and translated nitrum, that is, natron, or carbonate of soda. Boruk appears, however, to have been used in a generic rather than in a specific sense, as in the Persian works on materia medica (derived chiefly from the Arabic) which have been collated we find that no less than six different kinds of boruk (Persian bureh) are enumerated, of which some are natural, as the Armenian, the African, etc., and others artificial, as that obtained from burning the wood of the poplar, also that employed in the preparation of glass. Of these it is evident that the last two are chemically nearly the same, being both carbonates of alkalies. The incineration of most plants, as well as of the poplar, yields the carbonate of potash (commonly called potash, or pearlash); while carbonate of soda, or barilla, is the alkali used in the preparation of glass. Previous to the composition of bodies having been definitely ascertained by correct chemical analysis; dissimilar substances were often grouped together under one general term; while others, although similar in composition, were separated on account of some unimportant character, as difference of color or of origin, etc. It is unnecessary for our present purpose to ascertain the other substances included by the Arabs under the general term of boruk which may have been also included under the nitrum of the Greeks. It is evident that both the carbonate of soda and of potash were comprehended under one name by the former. It would be difficult, therefore, to distinguish the one from the other, unless some circumstances were added in addition to the mere name. Thus in the above passage of Jeremiah we have neter (nitre) and borith (soap) indicated as being both employed for washing or possessed of some cleansing properties, and yet, from occurring in the same passage, they must have differed in some respects. The term natron, we know, was in later times confined to the salt obtained chiefly from the natron lakes of Egypt, and neter may also have been so in earlier times. Since, therefore, the natural carbonate of soda is mentioned in one part of the verse, it is very probable that the artificial carbonates may be alluded to in the other, as both were in early times employed by Asiatic nations for the purposes of washing. The carbonate of potash, obtained from the burning of most plants growing at a distance from the sea or a saline soil, might not have been distinguished from the carbonate of soda, produced from the ashes of plants growing on the shores of the sea or of saltwater lakes. Hence it is probable that the ashes of plants, called boruk and boreh by Asiatic nations, may be alluded to under the name of borith, as there is no proof that soap is intended, though it may have been known to the same people at very early periods. Still less is it probable that borax is meant, as has been supposed by some authors, apparently from the mere similarity of name.
Supposing that the ashes or juices of plants are intended by the word borith, the next point of inquiry is whether it is to be restricted to those of any particular plants. The ashes of the poplar are mentioned by Arabian authors and of the vine by Dioscorides; those of the plantain and of the Butea frondosa by Sanscrit authors — thus indicating that the plants which were most common, or which were used for fuel or other purposes in the different countries, had also their ashes, that is, impure carbonate of potash, employed for washing, etc. Usually the ashes only of plants growing on the seashore have been thought to be intended. All these, as before mentioned, would yield barilla, or carbonate of soda. Many of them have been burned for the soda they yield on the coasts of India, of the Red Sea, and of the Mediterranean. They belong chiefly to the natural family of the Chenopodeoe and to that of the Mesembryanthemums. In Arabic authors, the plant yielding soda is said to be called ishnan, and its Persian name is stated to be ghasul, both words signifying "the washer," or "washing herb." Rauwolf points out two plants in Syria and Palestine which yield alkaline salts. Hasselquist considered one of them to be a Mesembryanthemum. Forskal has enumerated several plants as being burned for the barilla which they afford, as Mesembryanthemum geniculatum and nodiflorum, both of which are called ghasul. Salsola kali and his Suoeda monoica, called asul, are other plants, especially the last named, which yield sal-alkali. So on the coasts of the Indian peninsula, Salicornia Indica and Salsola nudiflora yield barilla in great abundance and purity, as do Salsola sativa kali, and tragus, and also Salicornia annua on the coasts of Spain and of the south of France. In Palestine we may especially notice the plant named hubeibeh (the Salsola kali of botanists), found near the Dead Sea, with glass-like leaves, the ashes of which are called el-Kuli from their strong alkaline properties (Robinson, Bibl. Res. 1, 505); the ajram, found near Sinai, which when pounded serves as a substitute for soap (ibid. 1, 84); the gillu, or "soap plant" of Egypt (Wilkinson, Anc. Egypt. 2, 106) and the heaths in the neighborhood of Joppa (Kitto, Phys. Hist. p. 267). From these sources large quantities of alkali have been extracted in past ages, as the heaps of ashes outside Jerusalem and Nablus testify (Robinson, Bibl. , Res. 3, 201, 299), and an active trade in the article is still prosecuted with Aleppo in one direction (Russell, Aleppo, 1, 79) and Arabia in another (Burckhardt, Trav. 1, 66). We need not assume that the ashes were worked up in the form familiar to us, for no such article was known to the Egyptians (Wilkinson, Anc. Egypt. 1, 186).
The uses of soap among the Hebrews were twofold —
(1) for cleansing either the person (Jer 2:22; Job 9:30, where for "never so clean" read "with alkali") or the clothes;
(2) for purifying metals (Isa 1:25, where for "purely" read "as through alkali"). Hitzig suggests that borith should be substituted for berith, "covenant," in Eze 20:37 and Mal 3:1.