SCHUYLKILL PERMANENT BRIDGE. 37 



As fast as the painter proceeded in his work, an adroit 

 hand dashed on the sand and stone dust. This was 

 mixed in proper proportions, as to colour and con- 

 sistency, which is only to be known by preparatory ex- 

 periments; easily accomplished. It was thrown on 

 with a common tin dust pan. The sand and stone dust 

 must be free from moisture, or any tincture from ma- 

 rine salt. It was dried in the sun, or a large iron kettle 

 over a slow fire. A small proportion of />/aw^er of Paris, 

 was mixed with the sand and stone dust. A long trough 

 containing the sand and dust, was placed under the work; 

 and caught what did not adhere, so as to be thrown up 

 again and prevent waste. The dispatch with which this 

 operation can be performed, exceeded expectation, both 

 as to facility and oeconomy. With marble dtist, it may- 

 be made to imitate that stone. As soon as one coat is 

 dry, the other must be laid on. Two coats, well attend- 

 ed to, are sufficient. But this is left to the choice of 

 those, who think another coat is required. 



The joints are imitated by convex strips, sprigged on 

 the weather boarding ; and after the coating is put on, 

 they are penciled off, with white paint. 



The following is a recipe much followed, and with in- 

 variable success, for barns and other buildings, in the 

 country : and being particulai'ly applied to roofs, it is 

 called ^'' fire proof y 



Take 20 gallons of fish oil ; boil it 4 hours over a slow 

 fire; and skim it as the feculence rises. Put in it 12 

 pounds of rosin, or an equivalent proportion of clarified 

 turpentine. Before taking it off the fire, mix ten gallons 

 flax seed oil, boiled in the common way. Grind and 

 mix with the oil, a sufficient quantity of QcJire (of t{ hat 



