THEORY AND PRACTICE OF PAINT MAKING 103 



qualities of the semi-solid linoxin, for a number of reasons, one 

 of which may be mentioned, namely, that particles of the first, 

 or coarse, class have a determining size which is a large fraction 

 a heavy percentage of the total thickness of coating, and are 

 in some instances thicker in diameter than the thickness of an 

 oil coating not reinforced with the fine or fire group. 



" We must think of the coarser particles as piers. The mix- 

 ture of linoxin with the other two groups of particles in the spaces 

 between these coarser particles, or piers, is the true paint body 

 and consists of flat reinforced arches which have the extra support 

 of falsework, in the shape of the structural material on which 

 the coating rests. Asbestine pulp, a natural product and one 

 of our most important natural reinforcing pigments, serves not 

 only in the coarse group as supporting particles for the linoxin 

 arch, but also because of its peculiar properties serves the more 

 important purposes of reinforcement. It retains, no matter 

 how finely ground, its peculiar needle-like, or rod-like, form of 

 particles, and obviously serves the purpose of reinforcing the flat 

 arch of linoxin, exactly as iron bars or iron netting serve in rein- 

 forced concrete arches. The medium sized particles of the second 

 group of pigments produced by chemical alteration or precipi- 

 tation, serve the purpose of the broken rock in concrete, and 

 together with the coarser supporting particles and the finest 

 reinforcing particles, give minimum voids and a maximum 

 imperviousness to agencies of internal decay. 



" It goes without saying that the pigments of any one group 

 contain particles of dimensions which fall into the other two 

 groups, but no one pigment supplies the correct proportion of 

 each of the three required dimensions, and each pigment has so 

 large a percentage of approximate dimensions as to bar it from 

 exclusive use in the other two groups. Given similar homogene- 

 ous coatings under identical conditions, we recognize the law 

 that elasticity will vary directly with thickness. Direct deduc- 

 tion from this law teaches us that of two paint coatings equal 

 in wear, in strength, opaqueness, and in all other qualities except 

 thickness, we should choose the thinner coating. Therefore if we 

 have two paint coatings fulfilling every requirement, the first 

 compounded with pigments giving a thicker coating and the 

 second with pigments yielding a thinner coating, we must choose 

 the second formula and obtain the thinner coating. 



