Eric Flint: Grantville Gazette Volume 24

The volume of a liquid is measured by introducing it into a graduated cylinder of suitable size. The flow rate of a gas can also be measured (suitable examples exist at homes which buy natural gas for heating purposes).

Temperature is measured, of course, by a thermometer. The first thermometers were of the liquid-in-glass type; first water, then alcohol, and finally mercury. The liquid expands as the temperature rises. Sealing the tube was essential to avoiding pressure effects. Mercury is liquid from -39 to 357њC. To measure higher temperatures, a gas-in-tube thermometer can be used. Hydrogen thermometers are used up to 1100њC, and nitrogen to 1550њC.

There are many other principles on which a thermometer can be constructed. The platinum resistance thermometer (1886) has been used to measure temperatures in the -259 to 630њC range.

Gas pressures are measured with a pressure gauge designed to handle a suitable range of pressures. There are hydrostatic gauges (manometers) which observe the movement of a column of mercury in a U-shaped tube, flexible pressure sensors like the 1849 Bourdon tube (coiled tube which expands and causes arm to rotate) or the diaphragm gauge (membrane deforms under differential pressure), and thermal gauges which detect the change in heat conductivity of a gas. A primitive manometer was invented by Torricelli in 1643. In Grantville, we probably have diaphragm barometers in several homes, and the steam buffs have pressure gauges which can work up to probably ten or twenty times atmospheric pressure. pH is a measure of the acidity or basicity of a solution. You can measure it quantitatively with a pH meter; which is really a voltmeter with a glass electrode sensitive to hydrogen ions. There isn't any useful information about them in the encyclopedias, but it might be possible to reverse engineer them, and, if one of the chemists took a course in chemical analysis, they would be described there.

If a pH meter isn't available, then you can estimate pH by using one or more acid-base indicators. Those are chemicals which change color depending on the pH. The oldest indicator, litmus paper, was known to the down-timers. EA/Indicator mentions that a mixture of methyl orange, methyl red, bromothymol blue and phenolphthalein will change color continuously from red to violet as the pH varies from 3 to 10. Several of these indicators are discussed in slightly more detail in EB11/Indicator.

Safety Equipment

The hazards posed by chemicals are fire, explosion, and irritation, burning or poisoning through inhalation of vapor, or skin or eye contact.

Borosilicate glass or stainless steel vessels, goggles, wash stations, specialized fire extinguishers, and fume hoods are all taken for granted in the late twentieth century laboratory but will be quite new to the down-timers.

For further details on hazard control in industrial processes, see Cooper, "Industrial Safety" (part 1 in Grantville Gazette 17 and part 2 in 18).

Separation Processes

Many naturally occurring inorganic chemicals are found together with other chemicals, from which they must be separated.

Chemical processes may also yield a mixture of products. When the reaction is performed, you have to separate the product from whatever else is present. At the very least, there will be solvent. If the reaction didn't go to completion, then there will be some starting materials still around. If your reactants and solvent weren't pure, then you have to worry either about the original contaminants or what they might have been converted into.

Some reactions, by their very nature, create more than one product. For example, there are decomposition reactions, which break a large molecule into two or more smaller ones. And there are many reactions in which there is a "change of partners" (compound AB reacts with CD to form AC and BD, where A, B, C and D represent pieces of the reactants).

Separation of the mixture usually depends on the physical properties that differentiate the desired chemical from the others with which it is associated. But suppose that you need to separate X (desired) from Y (undesired), and you can't do so directly. Well, there are tricks that depend on the different chemical reactivities of X and Y. You could chemically convert X to Z, separate Z from Y, then convert Z back to X. Or convert Y to Z, and separate X from Z or even convert X to Z and Y to W, separate Z and W, then convert Z back to X.

The more common separation processes, and the related physical properties, are:

Distillation/Boiling/Condensation: Boiling point (vapor pressure)

Recrystallization: Solubility of Pure versus Mixed Solutes

Decanting/Filtration: Solubility in a particular solvent, and particle size

Extraction: Difference in solubility between two immiscible liquids

Stripping: Difference in solubility in a liquid and in a gas

Sedimentation/Centrifugation: Density

Magnetic Separation: Magnetism

The down-timers are familiar with simple boiling (distillation), but not with techniques such as fractional distillation and vacuum distillation. I will discuss the more advanced techniques in a forthcoming article on the organic chemical industry. Since the down-timers have only the vaguest concept of gases, they are unaware of the elements that can be collected by the liquefaction of air.

Recrystallization was used by Birringucio in the sixteenth century to purify leached saltpeter. (Bohm). In the simplest form of recrystallization, the crude material is dissolved in a minimum quantity of a single solvent, heated enough to bring it all into solution, and then allowed to cool. The principal component crystallizes out first, in a purer form. I am not sure that the down-timers know about multi-solvent crystallization. In any event, modern chemistry increases the number of solvents from which to choose. We are also now more aware of the importance of initiating the crystallization step by providing a seed crystal or creating a seeding surface.

The down-timers also know that some reactions form precipitates, which can then be separated from the remaining liquid by decanting the latter. And they filtered liquids through felt, paper, and porous stones. (Bolton). However, they only practiced gravity filtration, not vacuum filtration, and their filter materials can be improved upon.

The down-timers have prepared extracts, usually with water, of various plant tissues (and the aforementioned leaching is also a form of extraction). However, they haven't really exploited extraction with organic solvents.

Since the down-timers don't know of any gas other than air, and use air in chemical processes only as an oxidant, they aren't aware of the use of a gas to selectively remove a chemical from a liquid.

Density separation by gravity has been used since antiquity. However, centrifugal separation didn't begin until the nineteenth century (a centrifuge was first used separate cream from milk). A centrifuge artificially achieves a sedimenting force much greater than gravity, and hence can separate materials of different density much faster than gravity can.

The down-timers are barely aware of the existence of magnetism, and they lack powerful magnets. Hence, they haven't performed magnetic separations, e.g., of ferrous from non-ferrous metals in recycling operations.

Scaling Up

In the seventeenth century, there were chemical processes, like dyeing and tanning, which could be called industrial processes. Nonetheless, there was no industrial production of chemicals, with the arguable exception of refining ores to metals.

The first chemical compounds produced in reasonably pure form on a large scale were sulfuric acid (late eighteenth century) and soda ash (early nineteenth century). Hence, the down-time alchemists are not accustomed to operations on an industrial scale.