64 PAINT TECHNOLOGY AND TESTS 



Analysis of Iron Oxide Pigments. Because of the great 

 consideration now being given to iron oxide paints, the writer 

 secured a series of oxides widely used in this country, and has 

 determined the most important constituents of each. 



Basic Lead Chromate (American Vermilion). By boiling 

 white lead with chromate of soda and subsequently treating with 

 small quantities of sulphuric acid, American vermilion, or basic 

 lead chromate, is prepared. It contains 98% of lead com- 

 pounds, frequently free chromates, and has a gravity of 6.8. 

 The particles appear granular and large, frequently assuming 

 a square structure. % 



Red Lead. By the continued oxidation of litharge in rever- 

 beratory furnaces, red lead is produced as a brilliant red pig- 

 ment with a specific gravity of 8.7. The pigment particles 

 appear to be of many sizes, showing a slight tendency to form a 

 compact mass. 



Paranitraniline Red. Paranitraniline red, a very bright red 

 material largely used in tinting paints, is prepared by diazotizing 

 Paranitraniline in hydrochloric acid by means of sodium nitrite 

 in the cold. This compound is rendered insoluble when pre- 

 cipitated directly on barytes, by acting on it with an alkaline 

 solution of beta naphthol. It is the most stable and permanent 

 bright red organic pigment which the paint manufacturer uses. 

 The particles of this pigment appear in various sizes, due, no 

 doubt, to a massing of the particles in the precipitation process. 



Chrome Yellow. The neutral chromate of lead, made from 

 either the nitrate or acetate of lead and chromate of soda, finds 

 wide use as a tinting pigment. When precipitated on a white 

 pigment base, various trade names are given to it. The micro- 

 scope shows clearly the physical character of this pigment. 



Zinc Chromate. This pigment is made either from zinc salts 

 and bichromate of potash or zinc oxide heated with chrome 

 salts, frequently in the presence of acid. Like the rest of the 

 chromate pigments, it is a very slow-drying material, often re- 

 quiring over a week to set up, unless considerable drier is added. 

 In spite of the impurities which it carries, it has shown itself 

 to be one of the most inhibitive pigments known and -has 

 demonstrated its value in even small percentages in paints for 

 iron and steel. It dries to a hard adherent film that tends to 

 protect metal from. corrosion. 



