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I N T R O D U C T I O N,


An Account of an additional Apparatus for experiments on Air, and of the precautions proper to be attended to in the use of it.

HAVING made some improvements in my apparatus, for making experiments on different kinds of air, it will be most convenient, in pursuance of the method which I took in the first volume of these observations, to give a short account of the several parts of it, previous to my entering upon the detail of the experiments themselves; and likewise to be a little more particular in the account of some things of this nature, which I thought it unnecessary to dwell upon before, but which I now find it would have been useful to many persons, if I had explained more fully at that time.

I must acknowledge, however, that, with respect to many things, which those who are altogether unused to.experiments of this kind complain that they did not understand, till they faw me perform the ^operations in their

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