If the nitrum was carbonated alkali, there is reason to suppose that the ancients must have occasionally mentioned in their writings that it effervesced with acids. With the mineral acids indeed they were not acquainted; but they had vinegar, and that nitrum produced with this an effervescence had been known in the oldest times. A very clear allusion to this circumstance is found in the book of Proverbs, chap. xxv. ver. 20; where Luther however translates the word by chalk. Jerome, whose explanation I have already quoted, was in some degree acquainted with this phænomenon; and therefore to him the comparison of Solomon was intelligible[1218]. But at present I can produce no proofs from Greek writers; though they might have occurred during the use of nitrum in medicine, in consequence of which it was often put into vinegar.
We shall be further convinced what nitrum really was, when the uses to which it was applied, as mentioned in the works of the ancients, are considered. The most common, as soap was not then known, appears to have been in washing, a purpose for which our saltpetre would not be fit; besides, it is at all times too scarce and too dear. I shall not here adduce any proofs of its being employed in this manner, as they often occur, and as several have been already given in the preceding volume[1219]. Many salves and cosmetics were prepared with nitrum; and in all probability articles of this kind, used chiefly among the women, are to be understood by the term nitron parthenicon, which occurs in Nicholas Myrepsius, in the beginning of the fourteenth century; matronicon, mentioned by the same, and by Alexander of Tralles, about the year 565; and the nitrum matronale of Marcellus Empiricus, in the fifth century. That the use of it for washing still continues in the East, is confirmed in various books of travels.
The oldest glass, of the preparation of which any account is to be found in history, was made by means of nitrum or mineral alkali. For though I doubt that it could have been produced on the sandy banks of the Belus, where some merchants, when cooking, supported their pots with lumps of nitrum[1220], because sand is not so easily brought to a state of fusion; it at any rate remains certain, that this supposed fusion with our saltpetre is altogether impossible.
The use of nitrum for painting announces, without doubt, an alkaline carbonate, and not saltpetre[1221]; and the case is the same with the various uses in the cookery of the ancients, many of which we have still retained. It was added to bread in baking, according to Pliny[1222], in the stead of salt, but probably to promote its rising, for which purpose it is still employed by the Egyptians, as potash was by our bakers. For this use the mineral alkali was formerly brought from the Levant to France, till it was declared by the physicians to be injurious to the health[1223].
When meat which was too fresh was to be dressed, it was put into nitrum[1224], in order to make it tender; and, according to Forskäl and others, this is still practised in the East. Our cooks also know that smoked meat, fish and other dried provisions become more tender when placed in a ley of potash, or when a little potash is added while they are boiling.
Nitrum, however, was employed for curing articles of food which people wished to preserve. This appears to contradict what has been mentioned above; but in all probability a caustic sort was used for the former purpose; but for the latter a mild kind, mixed with a great deal of common salt. There were so many species, that some of them might have been applied to quite contrary purposes.
As I conjecture, the use of nitrum for causing chestnuts and other husky fruits to boil soft, was also known: to produce the same effect, potash is at present thrown among boiling lentils and peas. I am inclined to think that for this reason Apicius caused chestnuts to be boiled with nitre.
It is highly probable that this effect of alkaline carbonates induced agriculturists to believe that beans, peas, lentils and other leguminous fruits, if steeped, before they were sown, in water in which nitre had been dissolved, or if the dung spread over the earth had been mixed with nitre, the future product could be more easily boiled soft[1225]. However useful this addition may be in cookery, it would produce little effect on seed; and it appears to me that the old agriculturists placed little confidence in the last-mentioned use, because they were not agreed in regard to the result. Virgil and others seem to expect from it an increase of the fruit[1226]; but others, security against beetles, which eat the fruit and leave the husks empty[1227]. When cabbages were transplanted they were strewed over with nitre, and by these means were said to come sooner to maturity[1228]. Radishes also were treated in the same manner, or besprinkled with nitrous water, in order to make them more tender[1229].
A common method employed by the ancient cooks to give a beautiful green colour to pickled or boiled vegetables, was to add nitrum to them while boiling; but this effect could be produced by natrum, and not by the nitrum of the moderns, or that neutral salt called saltpetre[1230].
Among the oldest accounts of nitrum is that where it is mentioned as being employed for embalming dead bodies. It would be tiresome to read over and examine everything written on that subject by the learned; but this much I think is clear, that either the flesh, and in general the softer parts of the body could be corroded in the course of seventy days by the Egyptian nitrum[1231], which, as above shown, was burnt, and in general mixed with unslaked lime, and consequently caustic[1232]; or that the moist parts could be desiccated by carbonate alkali, in the same manner as the manufacturers of parchment purify and dry their skins by the application of chalk. That saltpetre in no case could be useful for this purpose needs hardly be mentioned.