and the fee wing Cottverjion of Water into Air. 4 i r> 
oil, or iron-filings to the lime, I got nothing from thefe mix- 
tures in glafs retorts helides fleam and inflammable air, from 
the decompofition of thefe fubftances containing phlogiflon. 
That there was nothing in the materials of which the 
earthern retort was made that neceflarily produced the air, was 
evident from my not fucceeding when I pounded a broken 
retort, and heated it, mixed with water, in one of glafs. 
Being latisfied that the produ&ion of air depended very much 
upon the retort itfell , 1 thought of ufing the retort only with 
water, but without any lime, or earthy fubftance ; and I found 
it lucceed far beyond my expe&ation. For when I put a fmall 
quantity of water into one of thefe retorts, and endeavoured to 
diftil it gently, I never failed to procure about an hundred ounce 
meafures of air ; and this I could do as often as I pleafed, with 
the fame retort, and without its lofing any weight; and the air 
produced in this manner had never any portion of fixed air in 
it, and was always but very little inferior to that of the 
atmofphere. 
In all thefe procefles I obferved, that very little of this air 
was procured till all the water that could be poured out of the 
retort was evaporated, for the difference in the produce was 
very little, whether I expofed the retort to the fire quite full of 
water, or with only about an ounce meafure of water in it, or 
even after letting it remain full fora fhort time, and then pour- 
ing out all that I could from it ; fo that it was only that water 
which was entangled, as it were, in the pores of the retort, 
and which had been in fome mealure united to the fubflance of 
it, that had contributed to this produ£lion of air. 
Thefe retorts (which Mr. wedgewood informs me are made 
of a mixture of frefh and of burnt Devonfhire pipe clay) are 
pervious to water, though not to air; fo that while the air is 
produced 
