No. 6. DEPARTMENT OF AGRICULTURE. 331 



REPORT OF THE CHEMIST. 



Bt Dr. William Fkuab, State College, Pa. 



The subject of paints, their purity and durability, possesses es- 

 pecial interest to the farmer because he uses far more paint than 

 the average citizen, and because for his uses paints of high dura- 

 bility are especially needed, since they are required chiefly for 

 application to the exterior of dwellings, barn buildings, fences and 

 implements. The experience of recent years and vague informa- 

 tion that has drifted through the community, have led many to the 

 belief thai; the paints and related materials on sale in xVmerican 

 markets are often far below standard in composition, durability 

 and other important properties. 



In order that the subject may be clearly understood, let us con- 

 sider briefly the essential characters of oil paints, the only kind 

 of paints important in this relation. Oil paints consist essentially 

 of two materials, a solid pigment and a liquid part. The liquid 

 part is primarily composed of one or more drying oils. For the 

 cheaper paints used in coating the outside of buildings, linseed 

 oil is the only drying oil largely employed, while for artists' pur- 

 poses, other oils, such as walnut oil, are used. 



ITie value of the drying oils for this purpose is due to their 

 property of drying when exposed in a thin layer to the air. When 

 thus exposed, the thin oil film rapidly takes up oxygen from the 

 air and forms a substance, varnish, which is both hard and tough; 

 that is, is not easily cracked or pulverized by exposure to varying 

 temperatures, vibration or light blows. 



Kx])erience shows, however, that when a hard oil finish on wood 

 is exposed to rain or sunshine, it rapidly loses its gloss and disin- 

 tegrates; hence such a finish prepared from linseed oil alone is not 

 sufficiently durable for an outside coating of wood structures. 



It has, however, long been known that if certain pigments be 

 thoroughly incorporated with the drying oil, a thin layer of paint 

 thus prepared, dries rapidly and forms a glossy, tough coat, which 

 is much more durable when exposed to the weather, protects prop- 

 erly seasoned wood from decay, and at the same time, because of 

 tlie variety of color that can be secured by the use of difi'erent 

 pigments, makes possible the use of paint for a much wider range 

 of di'coriitive effect. 



It may be noted in passing that even the most durable paints 

 are not absolutely impervious to moisture, but that damp air will 

 pass slovsiy through them to or out from thp wood they cover. 

 They do. however, prevent wood in contact with the air from ab- 

 sorbing large amounts of water, and also from contact with a 

 great v.nriety of organisms that tend to produce decay. In some 

 case.?, too. the pigments are poisonous to such organisms and might 

 serve in part to arrest decay already started. 



