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The INTRODUCTION,represents a glass syphon, in each leg ofwhich is an iron wire, of such a length,that there shall only be about half an inchbetween the heads of them. The syphonmust be filled with mercury, and each ofthe legs inserted in separate basons, alsocontaining mercury. After this, the sub-stance may be introduced into the syphonby means of a glass tube, and, being lighter,it will take its place in the bend of thesyphon ; which may then be placed nearthe opening of a small furnace, or in theapparatus described Fig. 3. when whateverlodges in the upper part of the syphon willbe converted into vapour, and the explosionwill be made in it by making the syphonpart of an electrical circuit. Mercury itselfmay be converted into vapour in the samemanner.

There is a great variety of methods ofmixing nitrous and common air, in orderto ascertain the purity of the latter ; amongwhich that contrived by Mr. Magellan hasthe recommendation of much ingenuity,as well as much simplicity. But the man-4

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