COMMERCIUM

Philosophico-teciinicum.

I. Description of a Portable Furnace for making experiments.

P ORTABLE furnaces have been generally contrived,not only with a view to the purposes of experi-ment, but likewise for answering in some degree thedemands of business. As the size, which procures them thislast advantage, renders them less fit for the first and prin-cipal intention; I have long endeavoured to contrive amore manageable, as well as less expensive furnace, forexperimental enquiries; and to bring these kinds of instru-ments as near as may be, in regard to the facility andthe conveniency of their use, to the fame sooting with theair-pump, the condensing engine, and other like instru-ments employed in philosophical researches.

The first hint of the apparatus here described was takenfrom the practice of an ingenious workman in gold ; whoemployed occasionally, as a melting furnace, two of thelarger kind of black lead pots, or blue pots as they aresometimes called, one inverted over the other. Fouror five small iron bars, pasted across the under-

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