446 THE KENNEDY PIPE SCRAPER — DOANE. 



When the pipes are cast they are coated with coal pitch varnish 

 to prevent rust and afford a smooth surface The following 

 clause is taken from the specification for pipe for our new supply 

 main : — 



Coating. — " All castings shall be coated inside and outside 

 before any rust sets in with coal pitch varnish consisting of a 

 good and suitable coal pitch of about the consistency of tar, 

 deoderized, and freed from its naptha and volatile constituents,, 

 and an approved fixed oil, derived from coal pitch or linseed oil, 

 in such proportions as shall make a firm and tenacious coating. 

 The temperature of the castings shall be about 300 degrees F- 

 when dipped, and upon removal from the bath they shall be so 

 dripped as to leave a coating of uniform thickness, without 

 retained puddles or pendant drops of varnish. The varnish 

 coating" when cool shall be smooth, toup'h, without' undue brittle- 

 ness, tenaciously attached to the castings and not liable to 

 abrasion with ordinary handling." 



This varnish is scratched, cut and broken by rough handling, 

 and, as ma}^ be seen by the specimen before you, does not pre- 

 vent rust. 



In Halifax an attempt was made to clean the old 8-inch pipes 

 w^ith hand scrapers. Sections of pipe were cut out at convenient 

 distances and the incrustation was bored or scraped out. The 

 cost of the work was 3750 a mile, the city supplying the neces- 

 sary new pipe and sleeves to make connections. This process 

 was too slow and expensive to be adopted for the large mains. 

 The city must not be deprived of water for more than twelve 

 hours at one time, and in case of fire, water would be needed at 

 short notice. 



The idea of utilizing the pressure in the mains to drive 

 scraping machines originated with Mr. J. G. Appold, M. Inst. 

 C. E., and the apparatus was invented by him. In 1873, Mr 

 Thomas Kennedy, the Managing Director of the Glenfield Co., 

 Kilmarnock, Scotland, devised a modification of the Appold 

 Scraper, and this has been in general use up to the present time. 



In 1880, a Kennedy Scraper w^as imported from Scotland by 

 Mr. E. H. Keating, M. Inst. C. E., then City Engineer of Halifax, 



