102 PAINT TECHNOLOGY AND TESTS 



1 It is a fact that with particles of different sizes as against 

 uniform size the densest mixture can be obtained. This is so 

 evident as to require no proof. 7 It follows that the least density 

 and hence the largest percentage of voids occur when the grains 

 are all of the same size, and it is shown that the most voids occur 

 in a mass of large particles. The least voids occur when the 

 voids between the large particles are filled with smaller particles 

 and when these smaller voids between the smaller particles are 

 in turn filled with still finer particles. In other words particles 

 with three determining sizes will fill up a given space more com- 

 pletely than particles of two determining sizes and very much 

 more completely than particles of one size. 



Elasticity and Strength. " The paint coating here again is 

 governed by many of the laws which govern the similar material, 

 i.e., concrete. We find, by again referring to Taylor & Thompson, 

 on Concrete, page 275, that tests at the Watertown Arsenal on 

 concrete convinced the investigators that the ultimate strength 

 of a concrete is identical with the shearing strength of particles 

 of stone making up the aggregate. 



" This means that in its ultimate form the good concrete will 

 crack or shear through the broken rock contained therein, and 

 resistance to shearing is directly proportionate to the strength of 

 the broken rock chosen for the mixture. The film of semi-liquid 

 linseed oil when fresh is extremely weak, but as it hardens, its 

 characteristics and physical properties will obviously be those 

 qualities which are a composite of the qualities of the solid par- 

 ticles and of the semi-solid linolein incorporated together in the 

 paint coating. These physical properties of the suspended and 

 incorporated pigments profoundly modify the film in this respect. 



" The dried vehicle, linoxin, is notable for its elasticity, and 

 it is weak in crushing and tensile strength, and in hardness or 

 resistance to surface wear. The fact that it is a semi-solid 

 furnishes an opportunity to modify and improve those charac- 

 teristics of a solid in which it is deficient. The semi-solid, rubber- 

 like linoxin between the coarser particles of the pigment obviously 

 uses these coarser particles as supporting points. The medium 

 sized particles of the second group of alteration products serve 

 the same purpose as the broken rock in concrete. The coarser 

 particles absolutely do not, and can not, serve the purpose of 

 stiffening or of reinforcing or modifying the consistency and 



