PAINTING. 255 



and linseed-oil, as a base, with copal resin, thinned with tur- 

 pentine, subjected afterwards to a slow heat in an oven or 

 furnace, a process of baking. Trays, ornaments, door-locks 

 and knobs, and small articles have been successfully treated 

 to this process, and of late, experiments upon a larger scale 

 have been made. 



Practical Considerations. While the adoption of such 

 processes is known to afford more effective preventatives to 

 metallic corrosion than any other method of covering so far 

 developed, the effect upon the metal itself, the cost and in- 

 convenience of operation, and the necessity of especial appli- 

 ances would seern to debar such means from practical and 

 general use for the protection of structural material, fre- 

 quently in heavy masses; depending for its usefulness upon 

 its certain and known strength, and whose manufacture, com- 

 mencing at the mill, continuing at the shop, and possibly 

 proceeding at remote points of erection, seems to permit the 

 employment of no means which is not simple, convenient, 

 speedy, and economical, which conditions are more nearly ful- 

 filled by the protection afforded metals through paint-films, 

 and it would therefore appear that, comparatively, they are 

 the best protective coverings for iron or steel. As such agent, 

 the records of the past leave much to be desired, and it should 

 therefore be the serious effort of all engineers or other scien- 

 tists, both chemists and physicists, to continue in an effort to 

 develop this protective agency to the highest attainable 

 degree. 



Paint-films. Paint is used for purposes of ornamenta- 

 tion as well as for protection, but only in the last of these 

 functions .will it be considered here, where the practical, 

 rather than the aesthetic, is the prime consideration. 



Paint is a film of one or more coats or thicknesses, which, 

 may be applied or spread with a brush over any surface, and 



