HA7.1FAX WATER WORKS.— JOHNSTON. 103 



coating process of Dr. Aiio-ns Smith, whicii was first introduced 

 in the United States in 1858. The weight of experience seems 

 to show that in nncoated pipes the first ten or twelve veal's of 

 their life results in more or less rapid corrosion. After they 

 have l)ecome thoroughly tuberculated very slight changes take 

 jdace. If this is removed by scraping or cleaning it begins to 

 form again, and the life of the imcoated pi]>e l")ecomes mucli 

 reduced. 



The interior of coated pipes become tuberculated in the 

 same way, due to a large extent to defects in the coating, but 

 very much less tpiickly, a'nd Avhen removed by scraping the 

 iron is uninjured. The writer was present recently when a 

 piece of pipe was cut out of the 15-inch main, and when the 

 deposit was rubbed oif the coating was as sound and good as 

 when first put on. The outside of the pipe was also iti good 

 condition. The pipe had been cleaned a year previous, and 

 the tubercules had not beg-un to form, but there was a slight 

 deposit over the face of the pipe. The foUoAving points should 

 be obsen-ed in coating cast-iron water ]n]ies: — 



That the ovens in which the pipes are heated before being 

 dipped in the coal tar bath shall be so arranged tliat all portions 

 of the pipes shall be heated to an even tem[)erature. 



The ])ipes should be heated to a temperature of 300° F. 

 before being- dipped. 



The varnish to be heated to a temperature of not more than 

 300° F., and kept at this while the castings are in the l)ath. 



The ]ii])es should aot l)e submerged for less than five min- 

 utes, and Avlien taken from the bath should be evenly coated. 



Joints. 

 There are three kinds of joint.* in use in the water system, 

 — lead, wood, and turned and bored. Tiiese latter joints have 

 been in use since 1890, but they do not seem to find favor with 

 engineers in America and are very little used in Canada or the 

 United States; although in the Metropolitan Water AVorks of 



