STUDY OF DRIERS AND THEIR EFFECT 23 



A very small quantity of oil was placed in each of the can covers, 

 which were previously weighed, and allowed to distribute itself 

 over the bottom surface thereof. Reweighing of the covers 

 gave the amount of oil which was taken for each test. The 

 test samples in the covers were all placed in a large box with 

 glass sides, having a series of perforated shelves. In the side of 

 this box is an opening through which a tube was passed, carry- 

 ing a continual current of air washed and dried in sulphuric acid. 

 Oxidation of the oil films commenced at once, and the amount 

 of oxygen absorbed was determined at suitable periods by 

 weighing, the increase in weight giving this factor. This test 

 was kept up for a period of twenty days. 



A test was also made in the same manner with a current of 

 damp air passing into the box, to observe the relative oxida- 

 tion under such conditions. A chart of the results obtained 

 has been made (Table VI), to show the effect of the various 

 driers. 



Results of Tests. The following outline will present to the 

 mind of the reader the most salient points which have been 

 gleaned from these experiments, and which should give the 

 manufacturer definite knowledge as to the best percentage of 

 oxides to use either in boiled oil, paints or varnishes. 



In the case of lead oxide, an increase in the percentage of 

 lead oxide in the oil causes a relative increase in the oxygen 

 absorption, but when a very large percentage of lead has been 

 added, the film of oil dries to a leathery skin. 



In the case of manganese oxide, the increase in oxygen ab- 

 sorption on the first day is much more pronounced than is the 

 case with lead oxides. Furthermore, the oxidation of man- 

 ganese oils seems to be relative to the increase in manganese 

 up to a certain period, when the reverse of this law seems to 

 take place, and beyond a certain definite percentage of man- 

 ganese, added percentages seem to be of no value. It was 

 furthermore observed that the films dry to a more brittle and 

 harder skin than is the case when lead oxide is used. The oxygen 

 absorption with oils high in manganese has been noticed to be 

 excessive, and the film of oil becomes surface-coated, drying 

 beneath in a very slow manner; a condition that often leads 

 to checking. The critical percentage where the amount of 

 manganese appears to give the greatest efficiency seems to 



