74 PAINT TECHNOLOGY AND TESTS 



paints previously tested. After thorough drying for forty-eight 

 hours, there was placed on the surface of each board a few drops 

 of a solution of potassium ferrocyanide. This solution has the 

 effect of producing a blue coloration with iron sulphate, and in 

 every case when it was placed on a paint of considerable porosity, 

 the solution penetrated through and formed a blue coloration 

 beneath the paint. The results corroborated the original tests 

 referred to above. 



A series of sheets or films of paints were then prepared accord- 

 ing to the method referred to on page 71. These films were 

 placed over glass dialyzing cups, allowing the inner surfaces to 

 sag so as to hold a small amount of dilute ammonium chloride 

 solution. Distilled water was placed on the reverse side of 

 the dialyzing apparatus and the tests started. At the end of 

 six days the distilled water in each, test was examined and the 

 following results obtained: 



Test No. 1 (corroded white lead and asbestine film) allowed 

 the passage of 0.002 gm. ammonium chloride. 



Test No. 2 (corroded white lead and zinc oxide film) allowed 

 the passage of 0.0003 gm. ammonium chloride. 



Tests were also made with dilute solutions of other salts such 

 as ferric chloride, having a dilute solution of potassium sulpho- 

 cyanide on the reverse side of the apparatus. In the latter case 

 the formation of a pink color, characteristic upon the mingling 

 of these solutions, was obtained in a few hours. 



Film-Testing Machine. A film-testing apparatus, termed a 

 " filmometer " by its originator, Mr. R. S. Perry, was con- 

 structed, with the following features: A graduated upright 

 tube is fixed by means of sealing wax to two metallic plates which 

 carry an evenly bored hole, exactly under the hole in the up- 

 right tube. This hole measures exactly one square centimeter 

 in area, and is circular. The upright tube is graduated into lineal 

 centimeters and is called the pressure tube. 



Attached to the lower end of this pressure tube, close to the 

 metallic plates which serve as carriers for the paint film to be 

 tested, is a side-neck, which is inclined at an angle of 45 degrees 

 to the pressure tube, and serves the purpose of introducing the 

 mercury, as will be described later. Immediately under the 

 openings in the metallic plates which carry the film are arranged 

 two pieces of iron inclined at a 90-degree angle, so arranged that 



