ylir u/lJ hi the Blajl-Vurtiaci. 6j 



niercurv fupported was upwards of 7 inches ; the quantity of 

 air difchartred under fuch an impelhng power, I found to 

 exceed 2600 cubical i\^ci per minute. 



The coals ufed at tlie Cleugh, Cleland, and Clyde iron- 

 works, are nearly of the fame quality at each — a mixture ot 

 fplint and fuft coal. The Muirku-k and Glenbuck iron-works 

 have a coal difl'crcnt from any of the former, and in lome 

 particular fpots it confiderably refeniblcs the Englilh clod- 

 coal. 



2d, The various methods of procuring air for the blail- 

 furnace mav be reduced to the following : — lit. That pro- 

 cured by cylinders, a)ul difcharged into the furnace by means 

 of a floating pifton heavily loaded, and working in a large 

 receiver or regulating cylinder : 2d, That wherein pumping 

 cylinders only arc ufed, and the air thrown into chefts in- 

 verted in water, called the luater-vaidt : 3d, That mode 

 wherein tlie air is difcharged from the pumping or forcing 

 cylinder into an air-tight houfo, called the air-vault. 



The firft method is the original mode of blowing, and is 

 flill much ufed at thole iron-works whofe ereftion lias been 

 prior to the laft fifteen years. By this mode the quality of 

 the air is lefs fubjecl to alteration by a change of atmofphere. 

 The principal obje6lion to this manner ot blowing, is the 

 want of capacity in the receiving cylinder; which cannot be 

 increafed fo much as to take away the confiderable intervals 

 which occur at diflerent parts of the engine-ftroke. This 

 cfleft is fenfibly feen by the fpecdy and irregular afcent and 

 tlefcent of the column of mercury. In water blowing-ma- 

 chines, where the air is raifed by three or four cylinders 

 worked by means of a crank, where the air is received into 

 an air-chcft, and forced into the furnace by the continual 

 adlion of the blaft of each fucceffive cylinder, the current of 

 air is fleady, and fiipports the column of mercury with great 

 uniformity. 



The ufe of the water-vault has of late years become very 

 general among new erefted works. Its properties are, a {teady 

 asid very cold blad : the largenefs of the receiving ciftcrn-; 

 gives them a fufficient capacity to retain every pguad of air 



Vol.. VI. K railed 



