266 TOWERS AND TANK'S FOR WATER-WORKS. 



property of combination, resulting in the production of a 

 coating or film of a particularly tenacious, hard, and insoluble 

 character, when not subject to great heat or sulphurous gases, 

 which is seldom to be considered in connection with such 

 structures as towers and tanks. The'red-lead paint, however, 

 lacks elasticity, resulting in the formation of air-cracks, and 

 its porosity from the escape of volatile gases during the proc- 

 ess of hardening seems to be well established. Moreover, its- 

 high specific gravity has the disadvantage of causing the pigs 

 merit to " sag" or run away from the oil when being applied, 

 resulting in streaking or imperfect and uneven covering, 

 while its quick-setting qualities render this paint unsatisfac-. * 

 tory and difficult to handle. This last tendency may be in 

 part or entirely removed by the addition to the mixture of 

 carbon, usually in the form of lampblack, which further aids, 

 as has been shown, in diminishing the porosity offered as an 

 objection to the use of lead and oil, while if the paint is used, 

 as before erection, upon materials and surfaces which may be 

 placed horizontally or nearly so, the pigment has little or no 

 opportunity to settle out of the oil or "sag." 



For all the reasons submitted, it would appear that as a 

 priming coat, or first coat, red lead, lampblack, and linseed- 

 oil, when applied upon iron or steel surfaces of structural ma- 

 terial before erection, affords the best known protection to 

 metallic corrosion; it is also a well-established fact that red 

 lead, usually as a red-lead paste, is used in water and steam- 

 pipe fitting to produce a close and perfect joint, and that 

 when applied upon the laps of steel plate intended to be used 

 in water-tank construction, the same tendency toward pro- 

 ducing a water-tight joint is observed, and the use of this 

 material for such purposes minimizes the most objectionable 

 practice of making it necessary to resort to a natural or rust- 

 joint to secure the necessary degree of tightness between the 

 metal plates. 



