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called the Snift, through which this uncondenſed vapour is alternately forced, or blown out every ſtroke the Engine makes. For when the ſteam regulator opens, the piſton is at the bottom of the cylinder, and conſequently muſt by the firſt down ſtroke have pumped or forced out all the air, &c. that might have been previouſly mixed with the ſteam; the Engine will therefore rid herſelf partially of this vapour every ſtroke, if the quantity be abundant; and would finally and completely do it could the piſton be made, when it reaches the bottom of the cylinder, to fill every cavernous part. But as this cannot be, from the eduction pipe being only capable of diſcharging the water and not the air, &c. which is always uppermoſt, any vapour which remains in this part muſt be blown either through the ſnifting or the eduction valve; and is frequently diſcharged through both when the regulator opens.
Here, my Lord, I will advance ſundry reaſons why the veſſels Mr. Watt uſes, and calls Condenſers, cannot be cleanſed of water and uncondenſed vapour by the means above-mentioned; and ſhew that water only can (as in the foregoing inſtance) be diſcharged by a
gravi-
