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You might have noticed that my blog posts are sometimes spurred by perceived errors or mis-statements in other peoples works. I think it important that criticism is made and better information disseminated, and since I don’t own a newspaper or TV station, I have to make do with this blog. Also it often helps refine my own thought and provides a spur to reseach. I have often changed my mind/ position on something after re-reading and researching the subject. I also find that I understand and think about things better when contrasting them with other ideas rather than in a vacuum.

Today’s example is in Rasmussen, “Advances in 13th century glass manufacturing and their effect on chemical progress”, Bulletin of Hist Chem, vol. 33 number 1, 2008. Which can be found here.

It summarises various bits of research suggesting that Venetian glass makers in the 13th century improved their recipes by the use of Levantine plant ash. The use of these soda and quartz glasses, low in P and Fe and with increased lime and magnesium, would, he says, have given improved capabilities to withstand chemical attack. This part of the paper is clear enough, and I have no great quibble with it, although I have not read the papers he references to back up the physical properties of glass with such Mg and CaO contents.
The weakest thing is that he quotes only 4 different analyses of glass from Venice, which is hardly a representative sample. They are from the 9-10th century and 11-14th centuries, and so whilst they do show a difference in composition, I am still rather wary. It has happened before that someone has promulgated something that is correct with the backing of insufficient evidence, or made statements which suggest a greater accuracy and precision in dating than is acceptable from the evidence adduced. A lot of what he uses is circumstantial, such as dates and changes in practise and use which are not well understood. So this paper is perhaps better understood as offering a theory with further work required to re-inforce it. Or so I think.

A weakness is that I don’t see any discussion of how deliberate the changes in composition were.

Further small problems are:
On pages 31 and 32
Thus, eyeglasses, which nearly double the intellectual lifespan of the average person, affected the progress not only of chemistry, but science and technology in general.

That’s a huge leap of a statement, so greatly summarised as to be almost useless. Sure, they made some things easier, but people had gotten by well enough without them before. Rather, he should have emphasised that they made maintaining practical literacy more practical for those who could afford them which would have positive knock on effects. This statement doesn’t actually have a supporting reference for it… It would certainly be worth a large scale further study of evidence for it, and the working practises and importance or not of literacy. A counter argument is that the Romans didn’t have spectacles yet employed many older men in various capacities and had a reasonably high literacy rate, and it isn’t that important to read and write when you are an artisan, although there are some advantages to it, obviously. But if the Romans managed a Europe wide empire without spectacles, why are they so important a thousand years later? Roman engineering and technology was in many ways not as good as the high and late medieval period, yet better in some other ways, and they had a complex social organisation.

Later on, discussing the growth of stills, and use of glass for the alembic and later cucurbit, he claims that “clay” was used on the outside of the cucurbit, which is simply wrong, it was clay mixed with other substances, whether dung, sand or suchlike. Clay alone will tend to break off, and period recipes for lute on the outside of a vessel include dung or straw or such in with the clay. His reference for this is R. J. Forbes book “A short history of the art of distillation”, a by no means comprehensive early book on the topic. Once again this illustrates the dangers of innacuracy being transmitted by reliance upon older sources which do not cover the topic in enough detail.
Moreover, he writes:
This helped reduce breaking, but the poor heat transmission of the coating resulted in unnecessarily long preheating periods, thus making it difficult to distill volatile liquids such as alcohol.

Thus the dangers of a lack of experimental knowledge. In my experience a lute coating doesn’t make much difference to heat transmission, nothing that can’t be sorted by throwing a few more twigs on the fire, in fact in distilling acetic acid solutions I had great trouble keeping the temperature low enough, despite the lute covering the cucurbit. Next, a long pre-heating period and poor thermal transmission would be an asset in the distillation of alcoholic solutions, because the alcohol separates out better at lower temperatures, the higher the temperature the more water vapour is present, so the slower and lower the heating the better.

However, another factor was that even the most refined
alcoholic distillate separated by the early stills contained
so much water that it would not burn, thus making it difficult
to differentiate from normal water (34-36).

This is not necessarily correct. Butler and Needham (An experimental comparison of the East asian, Hellenistic, and Indian stills in relation to the distillation of ethanol and acetic acid, Ambix, vol. 27, part 2, July 1980) carried out some experimental distillations using laboratory equivalents of early still designs and didn’t have much trouble getting over 80% ethanol from a 46% ethanol mixture in one go.
The references 34-36 are to,
34. J. M. Stillman, The Story of Early Chemistry, D. Appleton
and Co., New York, 1924, 187-192.
35. Ref. 6, pp 86-87, 173-174.
36 L. Gwei-Djen, J. Needham, and D. Needham, “The Coming
of Ardent Water,” Ambix, 1972, 19, 69

His interpretation of what Stillman wrote is a bit odd, considering that Stillman quotes a number of 13th century and before sources which mention the making of a fiery water by distilling wine!
Instead, it seems clear to me now that although improved and more efficient cooling by the use of long tubes like serpents did make the production of alcoholic liquids more efficient and enabled it to be done on a bigger scale, that does not rule out their production in earlier times in a less efficient fashion. It might be that the liquids went from 10% to 50 or 60% ethanol, which is enough to catch fire when heated, and the introduction of the serpent permitted the maximum concentration possible, of 95% ethanol, at which point an azeotrope is formed and prevents further concentration.
Rasmussen seems unaware of much of this, and simply has not read or been aware of the more modern researches and has little idea of how well such distillations proceed in real life. Moreover, although the late Ahmad Al-Hassan had an agenda and drew many odd conclusions from his research, it seems to me that he presents enough of a case that Arabic alchemists and such did make and use a strongly alcoholic liquid. He was able to examine and read many Arabic manuscripts which of course earlier western researchers had no access to or were unable to read. (Studies in al-Kimya – critical issues in Latin and Arabic Alchemy and Chemistry”, Georg Olms Verlag, 2009, see chapter 9 for distillation of alcohol)

I am minded to think that there is more work to be done on the abilities of various forms of distillation apparatus at distilling alcohol. The key point is the cooling abilities of the earlier alembics (i.e. how much heat the substance of them can absorb) and their dependent tubes. Rasmussen and others depend mostly upon the appearance of some sort of serpent like tube running from the alembic which then carries out the condensing separate from the alembic and mark this as the true invention of strong spirits of wine. The earliest mentions are in the late 13th century, yet if C Anne Wilson is anything like correct in her works, such things might have been invented much earlier. But then her work is not so widely accepted, coming as it does from outside the history of science community and concentrating more on linking spirits of wine with Gnostic practises and knowledge. Thus it reads more like a book written by someone who thinks Roslin chapel really is connected to the knights Templar. Anyway, see “Water of Life”, Prospect Books, 2006, for more information. I’m not totally convinced myself, and it would surely be likely that if Hassan is correct that improvements in condensation were done by Arabic physicians and alchemists then transmitted to or independently re-invented in Europe.
More research is required.

Finally, Rasmussen states,
While earlier practitioners were well acquainted with the
vitriols (i.e. metal sulfates) and their calcination products,
the acid vapors had not been condensed prior to the 13th
century. It has been suggested that the newly formulated
retort may have been important in the preparation of the
mineral acids, as its one-piece design would have been
beneficial for such corrosive compounds (35). Without
doubt, glass or other still materials used for such isolations
required good chemical resistance, which may have
been the factor limiting an earlier discovery.

Certainly it is true that good glass vessels are required for acidic distillations, nevertheless he is, judging by both the works of Hassan and suggestive recipes in Arabic alchemical works, likely wrong about the condensation of such vapours. His reference 6 is to Forbes 1970 book, which as said above, is woefully out of date and simply a broad descriptive history of distillation. Certainly the one piece retort is not something I am familiar with in medieval alchemical works. They do appear in Biringuccio’s 1540 De Pyrotechnia, and I see one from a Syrian manuscript copied out by Berthelot, but finding good modern information on it is hard. I am pretty sure however that corrosive waters were not distilled in retorts, because I have not read of it. I have found a retort like vessel in Heironymous Brauschweig’s Book of distillation, for the distillation of herbs etc. So glass retorts were in Europe by the end of the medieval period, but looking at the shape I simply don’t see something which is good and useful for making mineral acids, given the extrememes of heat involved. They have too many curved surfaces and thus potential weak points. I think this is bolstered by the fact that Braunschweig was about distilling medical waters and Biringuccio features them as being for the distillation of oils.
So in this case it is likely that Forbes is wrong, simply because he didn’t have enough access to illustrations and books compared to nowadays.

The first part of the conclusion seems to me to be correct in general though:
A combination of the calcium and magnesium content
of the alkalis utilized and the purification of those materials
to maintain consistent properties allowed the glassmakers of Venice and Murano to produce superior glasses beginning in the 13th century. The quality of the
Venetian glasses dominated the European glass-making
industry until the 18th century and had a direct impact on
the advancement of the chemical sciences.

even if I disagree with the later parts.