92 PAINT TECHNOLOGY AND TESTS 



Observation of these results shows that pigments such as 

 Barytes, Blanc Fixe, and Silica have no chemical action on the 

 linseed oil. The results on Asbestine and China Clay also are 

 negative, the extremely slight increase in amount of ash from 

 these samples probably being clue to traces carried over mechani- 

 cally into the oil mixture; the last named pigments being more 

 fluffy and difficult to separate from oil. Slight action seemed to 

 be apparent in the case of whiting, a pigment somewhat alkaline 

 in nature. A longer test might have shown this pigment to have 

 possessed still greater action. Corroded white lead showed 

 considerable action, resulting in the formation of lead linoleate 

 or some other organic compound. Zinc oxide and lithopone, 

 the latter pigment containing 30% of zinc sulphide, both 

 indicated action on the oil. Chrome yellow (chromate of lead) 

 showed some action, as did also Prussian blue, the ash from 

 the last named pigment showing a heavy percentage of iron 

 oxide. 



Red Lead showed a most astounding gain in these tests, 

 chemical action of the pigment on the oil being apparent soon 

 after the tests were started, as shown by the formation of a 

 hard cake with the linseed oil. 



The Raw Linseed Oil which was used in these tests had an 

 acid value of 1.84%, which is very low. The neutralization of 

 this free fatty acid by some of the alkaline pigments used, may 

 account for part of the increased percentage of ash, but in most 

 cases the pigments, and more especially the basic pigments, 

 had a direct saponifying action upon the glycerides of the oil. 



