Of the DEVON IRON WORKS. 37 



the condenfation of the air thrown into the furnaces. I found 

 that a column of quick filver was raifed five inches, and fome- 

 times, though feldom, fix inches, and, in the interval of the re- 

 turn ,of the engine to receive air into the air pump, it fell only 

 half of an inch. At this time only one furnace was worked. 

 But when two furnaces were in blaft, the engine only raifed the 

 mercurial guage about 4 inches, becaufe the Devon Company, 

 for certain reafons, did not, while I continued a partner, think 

 proper to allow the blowing machinery to be completed, by the 

 putting to work their fecond boiler of 20 feet diameter for the 

 fire engine, according to my original defign, which, by adjufting 

 the machinery, would have enabled us to blow two furnaces, 

 with two boilers, with as much eflfedl, in proportion, as one fur- 

 nace with one boiler. This inftrument had the advantage of 

 enabling the work people to difcover the real power of their 

 blaft, and know the exadl condition of the air valves, and the 

 gearing of the blowing pifton ; for if thefe were not tight, and 

 in order, (although the engine might, to appearance, be doing 

 well, by making the fame number of difcharges of the air pump 

 as ufual per minute), yet the wind guage would not rife fo high, 

 and would Ihew that there was an imperfe<Etion fome where, by 

 reafon of a quantity of air efcaping at the valves, or pifton, that 

 could not fo eafily otherwife be known. This contrivance was 

 confidered as of much ufe, and was afterwards always quoted in 

 the Company's journal books, to fliow the adtual ftate of the 

 blowing machine, in comparing the daily produce of the fur- 

 naces. 



I HOPE you will not think me tedious, when I explain to yon 

 another experiment, which appears to me to be of confiderable 

 importance to all manufadlurers of caft iron. 



I HAD reafon to conje(flure, from my own obfervations on 

 the eflfedts of blowing machinery on blaft furnaces, as well as 



from 



