2^2 Dr. Priestley's Experiments and Obfcrvatlojir 



thing that I know to the contrary, the fame tnhe may ferve-. 

 for a very great number of proccffes, and perhaps the c'.ang^- 

 made in the in fide furface may protect it from any farther adion. 

 of the water, if the tube be of fufticient thicLnefs ; but thii 

 can only be determxined by experiment. 



Some eftimate of what may be expeded fi'om this method ofi 

 procuring inflammable air may be formed from the following* 

 ebfervations. About twelve inches in length of a copper tube, 

 three-fourths of an inch in diameter, filled with iron turning:^ 

 (which are more convenient for this purpofethan ironjilings, aa 

 they do not lie fo clofe, but admit the fteam to pafs through 

 their interftice>). when it was heated, and a fufficient quantity of 

 fteam pafl'ed through it, yielded thirty ounce meafures of air in 

 fifty feconds ; and eighteen inches of another copper tube, an 

 inch and a quarter in diameter, filled and treated in. the fame 

 manner, gave two hundred ounce meafures in one minute and 

 twenty-five feconds ; fo that this larger tube gave air in pro- 

 portion to its folid contents compared with the Imaller ; but to 

 what extent this might be depended upon I cannot tell. How- 

 ever, as the heat penetrates fo readily to fome diftance, the rate 

 of giving air will always be in a greater proportion than that cf 

 the fimple diameter of the tube. 



The following experiment was made with a view to afcertaia 

 the quantity of inflammable air that may be procured in this 

 way from any given quantity of iron. Two ounces of iron^ 

 or 960 grains, when diflblved in acids, will yield about 8o.<2> 

 ounce meafures of air ; but treated in this manner it yieldedi 

 1054 ounce meafures, and then the iron had gained ^zpgrainS' 

 in weight, which is little fhort of one-third of the weight of 

 the iron^ 



Confidering 



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