198 RICHMOND. 



Fehr " considers that the loss of mucilage is the most important result of 

 boiling oil, as it retards the drying, or more properly the hardening of the varnish 

 film. ' 



Mulder, 2 " on the other hand, found no difference in the drying properties of 

 raw linseed oil which had been filtered through charcoal, which must remove even 

 dissolved mucilage, since the filtered oil did not "break" on heating. 



This foreign matter designated as mucilage or albumin is present 

 in all expressed vegetable oils, but in such relatively small quantities 

 that it seems unreasonable to think its removal to be the main reason 

 for the specific treatment to which all raw oil is subjected in the prepara- 

 tion of boiled and varnish oils. 



Mulder 24 concluded that linseed oil which had only reached the first stage 

 in its oxidation contained free fatty acids. Bauer and Hazure 25 made the same 

 observation : "A sample of linseed oil four years old which was covered with a 

 thin skin, but otherwise completely soluble in ether, contained 8.9 per cent of 

 free acids. Another sample which had been stored in a badly closed flask for 

 five years contained 12.2 per cent of free acids." Lewkowitsch 20 gives the free 

 acid values calculated as oleic acid in weakly and strongly oxidized linseed oil 

 as 18 and 28.9 per cent, respectively. The acid values of some commercial varnish 

 oils recorded by Fahrion range from 13.4 to 32.6 per cent. According to Sadtler, 27 

 when linseed oil is boiled so as to have lost about 8 per cent of its weight, it is 

 converted into ordinary boiled-oil varnish, and if it is heated until it has lost 

 about 16 per cent of its weight it becomes thicker and yields a stiff varnish used 

 as the basis for printing inks. 



Linseed oil contains from 9 to 10 per cent of glycerol, which cor- 

 responds approximately to the loss in weight which the oil suffers when 

 converted into ordinary boiled-oil varnish, but boiled linseed oil also 

 contains considerable quantities of glycerol; hence other changes involv- 

 ing the formation of volatile products besides the hydrolysis of the 

 glycerides and the loss of the glycerol or its decomposition products, 

 acrolein and water, undoubtedly take place. The highly inflammable 

 nature of the gases which are given off when linseed oil is heated indicate 

 hydrocarbons and suggest more profound decompositions than mere 

 hydrolysis. However, linseed oil is not a very stable compound, con- 

 sisting as it does of weak acids in combination with a weak base ; and 

 whether the varnish oil is prepared by heat alone, or in conjunction with 

 added driers such as the oxides of manganese or lead, which are much 

 stronger bases than glycerol, considerable dissociation must necessarily 

 take place. In the case of the preparation of lithographic varnishes and 

 printing inks, where the chief requirement is a product which will not 



22 Loc. cit., 150. 

 . -"Loc. cit., 126. 



24 Loc. cit.. 8. 



25 Monatsh. f. Chem. (1888), 9, 459-468. 

 2G Oele, Fette u. Wachs (1905), 2, 592. 



-" Industrial Organic Chemistry. Philadelphia (1908), 101. 



