98 PAINT TECHNOLOGY AND TESTS 



between a film composed of solid particles cemented together 

 by a semi-solid homogeneous menstruum and a layer of concrete 

 composed of solid particles cemented together by a solid homo- 

 geneous medium. His application of the law permits the paint 

 manufacturers to design a paint formula with full knowledge of 

 the controlling conditions, so that it shall produce a coating 

 neither too thick, and therefore uneconomical and subject to 

 excessive internal strains, nor too thin, and thus weak and in- 

 efficient for protection. That Mr. Perry's contention was 



View showing careful Dressing of Bull Stone Mill from 

 Grinder 



well-founded, other paint technologists have since demonstrated; 

 notably Mr. Wirt Tassin, in his microscopic studies of paint 

 films in situ, and Prof. G. W. Thompson who, in his address to 

 the Penna. Association of Master Painters at Reading, said: 

 "I want to agree with Mr. Perry * * * where he says that a 

 pigment should be made up of particles of different sizes. Mr. 

 Perry also draws a further parallel between paint and concrete 

 where he refers to the form of the reinforcing pigment particles 

 and suggests that in paint coatings as in concrete a field can be 



