258 TOWERS AND TANKS FOR WATER-WORKS. 



ification, but with also a cement-like action, the substance 

 "setting " into a compact mass during a short space of time. 



Linseed-oil, then, alone or in combination with some in- 

 ert pigment or substance, absorbs oxygen rapidly and in con- 

 siderable quantities, wherever found, at the same time throw- 

 ing off volatile gases, becoming porous and absorptive as it 

 hardens into a tenacious, elastic vegetable gum ; while in so- 

 lution or combination with active mineral oxidizable com- 

 pounds, a radical change takes place, the resulting substance 

 being analogous to a metallic salt or soap, but evincing 

 cement-like properties. 



Pigments. Of the elementary substances as a base of 

 paint mixtures, it is generally conceded that Carbon C, as 

 lampblack (or graphite), or the hydrocarbon asphaltum has 

 given the best results for a metallic protective covering, while 

 in the opinion of many the metallic oxides as red oxide of 

 iron, (Fe 2 O 3 ) and the red oxide of lead (Pb 3 O 4 ) give equal or 

 better results. These substances have been used singly, in 

 combination with each other, or mixed with some of the 

 "inert" pigments, such as silica, kaolin, talc, whiting, gyp- 

 sum, etc. Comparisons, endeavoring to show why certain of 

 the many pigments should not be used, have been so often 

 made by eminent scientists that it. will be the attempt of the 

 author to give some reasons for the faith that is in him as to 

 why certain of these bases should be used upon metallic struc- 

 tures, such as stand-pipes, not affected by heat or by sulphur- 

 ous gases. 



Before the American Society of Mechanical Engineers, 

 June, 1895, Mr. M. P. Wood, a member of the society, read 

 a paper entitled " Rustless Coatings for Iron and Steel," 

 which is remarkably clear and interesting, and from which 

 is quoted the following: 



"Red Oxide of Lead, Pb 8 O 4 (Minium). This oxide is 

 found native in various parts of the world, mixed with other 



