=Panel No. 36--Lead Chromate.= This panel is in generally fair condition, but slight checking is shown. [Illustration: Perfect Condition of Plate Painted with Zinc Chromate; One Half Stripped. (_Negative cracked_)] =Panel No. 39--Zinc Chromate.= This panel is in condition similar to Panel No. 34, presenting a perfect appearance, with decided maintenance of color, elasticity of film, and freedom from any bad characteristics. It has proved to be one of the highest type rust inhibitive pigments. =Panel No. 40--Zinc-and-Barium-Chromate.= Although the color of this pigment is not very pleasing, it has proved itself to be the equal of zinc chromate in its protective value. =Panel No. 41--Chrome Green.= In excellent condition. Presents an appearance similar to Panels Nos. 34 and 39. Its surface is perfect and will doubtless give service for many years. =Panel No. 44--Prussian Blue.= This panel stands forth as the most wonderful moisture-excluder in the whole test, its surface presenting an appearance similar to a varnished plate, even after three years' exposure. Action between the pigment and the oil, resulting in the formation of iron linoleate, may account for this property. =Panel No. 45--Prussian Blue.= In same condition as Panel No. 44. =Panel No. 48--Ultramarine Blue.= Soon after this test was exposed, early vehicle decay and excessive chalking were observed. The admittance of moisture may have caused the formation of acid with the sulphur content of the pigment, which would account for the rapid corrosion which followed. It is of a pronounced stimulative type. The effect of stimulative under-coatings is well shown on some special plates on the fence, which when received were not pickled before painting, but had upon their surfaces the ordinary coating of mill scale. Over this had been stencilled in a triangular form the trade mark of the manufacturer. The stencilling material was made of ultramarine blue. When these plates were painted with some of the special paints, and exposed, the stimulative nature of the ultramarine blue began to assert itself, and within a short time, wherever the stencil marks were located, signs of rust began to appear through the coatings of top paint which had been applied. Corrosion under these stencil marks became so great that the trade mark was plainly outlined in letters of rust. This would seem to be final proof that pigments of a stimulative nature should never be used for the priming of iron and steel. =Panel No. 49--Zinc-Lead Chromate.= In excellent condition throughout, with a smooth surface and showing no corrosion. Stands in the same class as Panels Nos. 34 and 39. [Illustration: Effect of Stimulative Paint. Manufacturer's Trade Mark Stencilled on Bare Metal in Triangular Form, showing Through Subsequent Paint Coating] =Panel No. 51--Black Magnetic Oxide of Iron.= In excellent condition. CHAPTER XVII THE SANITARY VALUE OF WALL PAINTS