20 June 2006

Berg’s Project: Berg’s Sources of Information

It is unusual to have so much information about the chemical formulas developed by an amateur chemist. It is equally unusual to have the quantity of information about sources that Berg’s experiment book provides. In his efforts to learn both chemistry and glassmaking, Berg read special and general treatises, he received advice from experts, and he examined the objects he made. He repeated experiments described to him and created new ones, relying not only on the knowledge of other artisans but also on his own developing skills.

Berg identifies many of his printed sources: the first page of the first notebook lists both Peter Shaw’s Chemical Lectures (first printed in 1734) and James Millar’s New Course of Chymistry (1754). Berg incorporated into his experiments a number of Shaw’s recommendations and comments about glassmaking; his use of Millar is less obvious. Other notebook entries record verbal transmissions of information, confirming Berg’s work with chemists, goldsmiths, color manufacturers, glass house proprietors, and glass merchants. Some of those conversations offer still other sources of information he used. For example, he notes, “Mr. More inform'd me that a French Author he had read, says that Iron may be fixed by calcining it with Common Salt.” The “French Author” is almost certainly Pierre-Joseph Macquer, whose Elemens de chimie pratique was published in 1751, and available in English translation within a few years. In this case, Berg’s note continues with a description of why iron oxide is made more stable by heating in a closed container with salt: the combination of salt with vitriolic acid from the iron forms “a kind of Glauber’s salt,” which will be dissolved in washing. Berg then incorporates that description into explanations of certain experiments, just as he describes his use of iron oxide prepared in this way.[10]

The collection of material in the experiment book suggests Berg’s reconciliation of the practical and the philosophical in other ways as well. In 1766, he calculated the proportional gravity (specific gravity) of several samples. This number is probably related to a study by Edward Hussey Delaval, presented to the Royal Society of London in January 1765 and published in its Transactions later that year.[11] In his paper, Delaval established a relationship between color and density, suggesting that a more dense substance would reflect more refrangible rays. Berg does not explain how he used this calculation, however. Perhaps it allowed him to compare different-colored results, or he may have used it to judge such characteristics as opacity—an important quality in glassmaking and one for which a regularized comparison method would have been helpful. Berg may have found that proportional gravity was not a useful calculation in his work, as after 1766 he no longer records this number.


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