Strictly copyright Singer, I hope he dosen't mind !354 PRE-SCIENTIFIC INDUSTRIAL CHEMISTRY
111. ALKALIS, CLEANSING-AGENTS, ACIDS
Soda and potash were in great demand as detergents and also for making glass, glazes, and soap. Their sources were native sodium carbonate, plant ashes, and calcined tartar.
Crude sodium carbonate or sesquicarbonate is found in quantities in various places in Egypt and notably in the famous Wadi Natrun which runs in the Western Desert parallel to the west limb of the Delta and about thirty miles from it. This native carbonate was known as nitrun. Of this word natron is a seventeenth-century European variant of the Arabic natru-n; hence natrium and our symbol for sodium. Important
in remoter antiquity (vol I, pp 259-60,268, 270) sodium
carbonate was little employed in medieval Europe,
though potash was in great demand.
Plant ash or 'pot-ash' contains a workable propor-
tion of potassium carbonate with a little sodium car-
bonate, unless it is derived from salt-marsh plants or
FIGURE 3:Z7-ScraPing tartarfrom seaweeds, in which case the proportion of the sodium
the inside of a wine cask. From a I
printed book, Strasbourg, c I497. sait is much larger. Wood-ashes were the normal
material for making glass, lye, and soap in north
Europe, and were even imported into England from the Baltic countries. For glassmaking the ashes of beechwood were recommended by Theophilus, but those of the bracken fern were especially esteemed and in England are said to have been used exclusively. For cleansing purposes, the ashes were extracted with water, yielding lye. For soap-making, lime was added to the wood-ash and water allowed to percolate through the mixture; the potassium c2rbonate was thus converted into caustic potash ('sharpening the lye'). The caustic solution was then boiled, or in some recipes merely stirred, with oil or fit.
In the Mediterranean area there was in general use a supposedly superior product, namely the fused ashes of a low woody shrub, probably Salsola soda L. This, when imported from Syria and the Levant, was called polverine or rocchetta; when brought from Spain, barilla. It contained UP tO 20 per cent of sodium carbonate and was effective for all purposes for which wood-ash was used; moreover, it contained more alkali and had the additional advantage of yielding a hard soap with fats, rather than a soft.
Tartar or argot is the deposit in wine-casks (figure 327). It consists chiefly of potassium hydrogen tartrate. When calcined it yields fairly pure potassium
FIGURE 327-ScraPing tartarfrom the inside of a wine cask. From a printed book, Strasbourg, c I497.
ALKALIS, CLEANSING-AGENTS, ACIDS 355
carbonate. Its chief use seems to have been medical, though it had some application in mordanting. The dregs of wine were sometimes dried and carbonized, giving a product (cineres clavelati) containing a high proportion of potash.
Ammonia was available in quantitv in the form of stale urine. This was much used for the purpose of cleansing from grease, for making alum (pp 215, 368),
and for pigments (P 36i).
Lime, formed by 'burning' chalk or limestone, was familiar. The kilns were simple, usually holes in a hill-side or low tower-shaped furnaces (figure 323), charcoal being used as fuel; coal, where available, was preferred in the Middle Ages. Lime was used in great quantity for Plaster, mortar, and attractum, the favourite mixture of lime, sand, and stones for filling the interior of thick walls. Mixtures of lime and sand were the chief medieval cement, but gypsum cements were also used. In Italy and the Mediterranean islands, pozzolanic cements (P 407), which would set under water, were made from volcanic tuff, lime, and sand; they have been used from classical antiquity to the present time. Pozzolana derives its name from the port of Pozzuoli, near Naples (figure 473).
Cleansitig-agents were used for personal hygiene and in the textile industry. The Greeks and Romans of the earlier centuries cleaned their persons by means of oil with or without mechanical a-ents such as bran, sand, ashes, juices of certain plants, and pumice. They were fond of hot, cold, and vapour baths. Various earths or clays were used for the hands. Soap, in our modern sense, . seems to have been unknown to them; it may have been a Teutonic or Tatar invention. It became known about the beginning of the Christian era, and was at first regarded rather as a cosmetic or medical preparation (see below).
Clothes were cleansed in antiquity with fuller's earth (a hydrated aluminium
silicate) and alkali. The former absorbs fat, the latter forms soluble compounds si
with it. The alkali usually employed was urine that had become ammoniacal, but sometimes lye from natron or wood-ash was used. The action of these substances was aided by mechanical beating in fulling-mills (figures i 87, 553). These remained in use until the close of the Middle Ages, and for long after soap had
become a familiar article of commerce.
Soap is of obscure origin. The Latin word sapo from which it comes is used by Pliny to describe a pomade invented by the Gauls. As this came to be extensively imported into Rome it is not safe to translate sapo by 'soap'. The first reference
in which this rendering is fairly certain is Of C A. D hys'cian Pr' '
. 385 by the p i iscian,
who speaks of it as used for shampooing. By 8oo its manufacture was a common domestic craft in Europe, and from then on we hear frequently of the calling of soap-boiler. From the twelfth century, at least, soap was produced in large
356 PRE-SCI'ENTIFIC INDUSTRIAL CHEMISTRY
quantities, and became a major export from several countries, notably Scandinavia. At first soap was made from animal fats and had a very unpleasant smell. This was overcome by the discovery that olive-oil could be used for the purpose, after which much of the trade passed to Spain and the Mediterranean region.
Hard soap was made around the Mediterranean from olive-oil and soda-ash (rocchetta or barilla). It was first produced by the Arabs and later made especially in Castille, Marseilles, and Venice, and exported to the northern countries. It was often perfumed and was regarded as an article of luxury.
Soft soap is typically a potassium compound. In the northern countries great quantities of it were made for textile-cleansing, at least as early as the twelfth century. The alkali used was caustic potash lye made by running water through layers of wood-ash and lime. The fat was tallow or whale-oil or other animal fat. The soap was of industrial application rather than a luxury article. Recipes of the sixteenth century indicate that some soap was made by simply stirring together hot lye with oil and letting them stand until they had thickened. Some was made by boiling fat with weak lye until saponified. The process of 'saltingout' is not recorded until the seventeenth century.'
Nitric acid. The notion of acids as a class was not developed until the sixteenth century, although certain acids had been familiar from antiquity. There is no Latin description of the preparation of nitric acid before the Summa perfectionis of Geber [I3], though such a description is given by the Arabic jibir. Nitric acid is also mentioned in treatises falsely ascribed to Ram6n Lull (I 23 5 ?I3I5), but written after I330. It was made by distilling nitre (P 370) with sulphates of aluminium, copper, or iron, previously partly dehydrated. A high temperature was required, and the distillation-apparatus had to be resistant to heat and acid vapours. The industrial use of the acid was in the separation or 'parting' of gold from silver, the silver dissolving and the gold remaining.
Aqua regia. Geber says, correctly, that the addition of sal ammoniac to nitric acid enables it to dissolve gold. This mixture, aqua regia, containing hydrochloric as well as nitric acid, could be used to separate silver from gold. The gold dissolved to a soluble chloride, while silver was attacked and precipitated as an insoluble chloride. The gold could readily be recovered by evaporation of the
I Oils and fats are essentially esten of gl),cerol with fatty acids. When an alkali such as soda is made to react with a fat, the sodium salt of the fatty acid is formed and glycerol liberated. In the earlier methods of soapmanufacture the glycerol remained in the product. It hw, however, no detergent action and can be removed by adding salt to a soap solution. This throws the soap out of the solution, and leaves a pro of glycerol in the
brine. 'ne operation may be repeated until the major part of the glycerol has been Nowadays the glycerol is recovmd, as a valuable by-product.
CERAMICS AND GLASS 357
liquid and heating the residue, while the silver could be obtained by smelting the chloride with an alkali. Nitric acid was suitable for separating small quantities of gold from silver, and aqua regia for separating small quantities of silver
from gold.
Sulphuric acid has a history that is far from clear. There is hazy evidence that it was made by Arabic-speaking alchemists as early as Jdbir (P 736). However, it is not certainly known to have been isolated before c I535. Thereafter it was made both by burning sulphur and condensing the traces,of acid so formed, and by the distillation of green or blue vitriol (iron or copper sulphate). It did not become of industrial importance until the seventeenth century. Nevertheless, the acid had been employed in vapour form for many centuries, both in the cast and in the west, in the cementation process for purifying gold by heating it with
vitriol and salt.
Hydrochloric acid similarly had been produced, but was not isolated or reco&-
nlzed until the seventeenth century. Organic acids such as vinegar (vin-aigre)
from wine turned sour, or merely the juice of sour grapes (ve 'uice), have been in
ri
general domestic use from an early date (vol 1, pp 284-5).
From Singer History of Technology
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www.circa1265.co.uk (medieval)
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posted 12-02-2000 09:07 AM
posted 12-05-2000 08:20 AM
posted 12-06-2000 01:34 PM
posted 12-08-2000 08:25 AM
is there an appreciable difference between medieval methods and handmaking soap now? 'Now' consisting of distilling lye from wood ash, rendering tallow for lard, heating the mix, cooling the mix, adding tinctures from botanicals or essential oils for color and/or scent, forming the soap, etc.
