===============================+==============+======================== | Per cent. of | | Ash in Oil | Pigment in Oil |Extracted from|Analysis of Ash | Oil-Pigment | | Paste | -------------------------------+--------------+------------------------ Raw linseed oil without pigment| 0.003 | -- Barytes | 0.003 | -- Blanc fixe | 0.003 | -- Silica | 0.003 | -- Asbestine | 0.005 | -- China clay | 0.007 | -- Whiting | 0.008 | -- Chrome yellow | 0.025 |Lead oxide (PbO) Lithopone | 0.031 |Zinc oxide (ZnO) Prussian blue | 0.032 |Iron oxide (Fe_{2}O_{3}) Sublimed white lead | 0.033 |Lead oxide (PbO) Zinc oxide | 0.105 |Zinc oxide (ZnO) Corroded white lead | 0.116 |Lead oxide (PbO) Red lead | 0.2112 |Lead oxide (PbO) ===============================+==============+======================== 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 due to traces carried over mechanically 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. CHAPTER V