2^1 Dr. Priestley's Experiments and Objcrvatlons 

 I found to anfwer very well during the procefs, though they 

 never failed to break in cooling. At length I procured a tube 

 of copper^ on which, as M. Lavoisier difcovered, fleam had 

 no effect ; and at iafl: I made ufe of earthen tubes, with which 

 Mr. Wedgewood, that mod generous promoter of fcience, 

 liberally fupplied me for the purpofe ; and thefe glazed on the 

 outfide only I find far preferable to copper. They are, indeed, 

 every thing that I could wifli for in experiments of this kind; 

 the reafcn of which will appear in my account of another courfe 

 of experiments, which I hope to lay before the Society in due 

 time. 



The difpofition of the apparatus, with which thefe experi- 

 ments were made, was as follows. The water was m.adeto boil 

 in a giafs retort, which communicated with the copper or 

 earthen tube which contained the charcoal or iron, &c. and 

 which, being placed in an horizontal pofition, was furrounded 

 with hot coals. The end of this tube oppofite to the retort 

 communicated with the pipe of a common worm tub, fuch as 

 is generally ufed in diflillations, by means of which all the 

 fuperfluous fleam was condenfed, and colle(5led in a proper re- 

 ceptacle, while the air which had been produced, and had 

 come along with it through the worm tub, was tranfmitted 

 into a trough of water, where proper veflels were placed to- 

 receive it, and afcertain the quantity of it ; after which I 

 could examine the quality of it at leifure. 



In the experiment with charcoal^ I found unexpe6led diffi- 

 culties, and confiderable variations in the refult ; the proportion 

 between the charcoal and water expended, and alfo between each 

 ofthemani the ^/r produced, not being fo nearly the fame 

 as I imagined they would have been. Alfo the quantity of 

 fixed air that was mixed with the inflammable air varied very 

 4 much. 



