MECHANICS AND USEFUL ARTS. 59 



jagged with tubercles of various sizes and shapes, occurring at 

 irregular intervals. 



Tlius far no satisfactory explanation has been given of the 

 causes of this peculiar deposit. That it is a species of oxidation 

 is very clear, since the mass formed has all the external character- 

 istics of iron-rust ; but why it should assume such peculiar physi- 

 cal properties, and present a configuration so unlike the outward 

 forms of other oxidation, has not yet been satisfactorily ex- 

 plained. 



The effect of this incrustation is obviously very disastrous to 

 the economical distribution of water, as the diameter of the mains 

 is so much diminished as to reduce their capacity to that of much 

 smaller calibre than they were originally constructed. In addi- 

 tion to this, the strength of the pipe is much impaired by this 

 process of oxidation, and it is rendered much less able to bear 

 sudden concussions and heavy pressure than previous to the 

 formation of the deposit. This must be apparent to all intelli- 

 gent observers, for it is at the expense of the iron that the incrus- 

 tation arises. These facts are but too well known to engineers, 

 who are fully cognizant of the difficulty under which they labor 

 in endeavoring to remedy the evil. 



The same evil obtains in regard to gas-pipe, only in a less 

 degree. The corrosion forms dust and scales, which drop off in 

 time, and obstruct valves, traps, elbows, and connections. This 

 is especially observable in inclined and vertical piping, such as 

 lamp-posts, etc. 



It has been a question with practical men, whether to substi- 

 tute some other material for iron, or to adopt some means of 

 internally coating iron mains, so as to preclude all possibility of 

 the formation of accretions. 



Methods have been tried to coat the interior of iron water- 

 pipes with some substance which would protect the surface of 

 the iron from contact with the water. This would seem to be the 

 only remedy, but attempts in this direction have heretofore been 

 attended with so much expense as to remove one of the strongest 

 arguments in favor of the employment of iron, namely, the econ- 

 omy of its application. Some few years ago, the AVater Board 

 in Brooklyn coated the interior of their iron main with a mixture 

 of coal tar and linseed oil, applied at a high temperature, but we 

 have never heard whether that remedy has been effectual in 

 checking the formation of accretions. It was said to impose an 

 additional cost of 2 dollars per ton on the mains. 



Recently, Prof. Henry Wurtz, of New York, has invented a 

 peculiar cement for making gas or water pipes, and especially 

 adapted to coat the interior of gas mains, to make them perfectly 

 impervious even to hydrogen gas, and to prevent corrosion. 



Among the materials, other than iron, which have been com- 

 mended and used to some extent for water pipes, "are wood; 

 iron-bound wood, and cement, and bituminized paper. 



Plain wooden pipes have been inimemorially employed in some 

 places for distributing water, and are still used in many instances. 

 Pipes made of wood and cement have also been adopted to a liin- 



