62 CONSTRUCTION OF RETORTS. 



is the most valuable for this purpose, and is used in all places where heat is 

 present. It may be compounded as follows. To one ounce of sal-ammoniac, 

 add one ounce of flowers of sulphur, and thirty-two ounces of clean cast-iron 

 borings : mix all well together, and keep the composition dry. When the 

 cement is wanted for use, wet the mixture with water, and when brought to a 

 convenient consistence, let it stand for a few hours ; then apply it to the joints, 

 and screw them together. The flanches ought to be kept about three-eighths of 

 an inch apart, by wrought-iron wedges, and the cement well filled in between 

 them with a square blunt-pointed chisel, called a caulking-chisel ; the cement is 

 stopped from being driven through by a hoop of thin iron placed inside the 

 pipe or retort to be thus operated upon, which is afterwards removed. A con- 

 siderable degree of action and reaction takes place among the ingredients, and 

 between them and the iron surfaces, which causes the whole to unite as one 

 mass ; the surfaces of the flanches become joined by a species of pyrites, all 

 the parts of which adhere strongly together. Mr. Watt found that the cement 

 is improved by adding some fine sand from the grindstone trough. 



A very ceconomical joint for the retort mouth-piece is made of five parts of 

 fine Stourbridge clay, and one part of the mixture just described. 



For some purposes it is more convenient to join the parts not exposed to 

 heat, with putty, mixed to a proper consistence, and applied on each side of a 

 piece of thick canvas, flannel, plaited hemp, or a piece of thick pasteboard 

 steeped in linseed oil (previously shaped to fit the parts), and then interposed 

 between the parts before they are screwed together : it makes a close and du- 

 rable joint, and is generally used for those which have occasionally to be 

 opened, and for those which must be separated repeatedly before a proper ad- 

 justment is obtained. 



The face of the retort mouth-piece is bevelled inwards, and is chipped and 

 filed, if necessary, to remove any lump that would prevent the lid from fitting 

 close ; a clean and true casting, however, seldom requires this to be done. 



The lid is shown in Plate III. Figs. 6 and 7. It is jointed on to the face of 

 the mouth-piece, with "luting" made of the spent lime from the dry puri- 

 fiers, mixed with a little fire-clay, and tightened into its place by a strong, 

 square-threaded screw, and cross-bar of wrought iron, the ends of the cross- 

 bar being passed through projecting ears, against which it bears when the 

 screw is turned. 



B is -the "stand-pipe," through which the gas, as it is generated, passes 



