18 BTXLETIX 883, U. S. DEPARTMENT OE AGRICULTURE. 
the best quality. Information of such character is of the utmost importance in con- 
nection with the production and improvement of this staple crop. However, it is 
not only important to ascertain the high oil-yielding varieties of seeds but the proper- 
ties and general behavior of the oils are of equal importance. The physical and 
chemical properties of the oils determine their value to a large extent. In order to 
facilitate the best comparison, only those properties which admit of accurate measure- 
ment and which have a direct bearing upon the quality of the oils were considered. 
Color, specific gravity, and index of refraction are important physical properties 
in which variations can easily be detected. . . . The specific gravity and the 
refractive index, which have much significance as regards the general composition 
of the oils, were readily determined. 
The chemical properties are perhaps most important from the standpoint of the 
composition of the oils. The acid, saponification, and iodin values are the most im- 
portant chemical constants. The acid value of the linseed oils is affected by a number 
of conditions. Factors such as rain or moisture during harvest and the storing of the 
moist flax after harvest, which would tend to produce molding of the seed, will modifv 
considerably the acid A^alue of the oil. The saponification value representing the 
sum of the acid and ester values is a combined measure of the free acids and glyceryl 
esters contained in the oil. 
Linseed oil consists for the most part of glyceryl esters of linoleic and linolic acids. 
These unsaturated fatty acids possess the property of absorbing iodin. This property 
is known as the iodin value and is perhaps the most important of the chemical con- 
stants. The iodin value is a direct criterion of the proportion of these fatty acids 
present in the oil, and since these acids determine the drying property of linseed oil 
the iodin value becomes an index of this property. 
The usefulness of linseed oil in the industries is based upon the property of the 
oil to dry to a tough elastic film when exposed in thin layers to the air. This oil is a 
typical example of a class of fatty oils known as drying oils. Oils of this character 
are composed largely of glycerids of unsaturated fatty acids which possess the property 
of absorbing oxygen when exposed to the air. The absorption of oxygen by linseed 
oil alters its composition and is accompanied by the formation of a compound known 
as linoxyn. which constitutes the tough elastic skin so familiar when the oil is allowed 
to dry. The usefulness of linseed oil as a protective coating is due entirely to the 
formation of the compound linoxyn, which is resistant to the effects of heat and mois- 
ture of the outside elements to a remarkable degree. 
Coincident with the absorption of oxygen there occurs an increase in the weight of 
the oil, and the more rapid the increase in weight the greater is the rapidity of drying. 
and vice versa. Advantage was taken of this property in order to determine the 
relative drying value of the A-arious oils under consideration. 
Two methods were used for the extraction of the flax samples, namely, ether extrac- 
tion and cold expression. The former method was applied to determine the actual 
yield of oil in the seeds, while the method of cold expression was employed to obtain 
working samples of the various oils for the determination of the physical and chemical 
constants. Ether extractions were made by means of the customary Soxhlet extrac- 
tors, while a small laboratory hydraulic press served for the cold expression of the oil. 
The yields of oil given in all cases represent ether -extracted oils, whereas all physical 
and chemical properties were determined upon cold-pressed oils. 
It must be borne in mind that these cold-pressed samples differ from ordinary 
commercial raw linseed oils, being obtained under entirely different conditions. 
The results obtained are therefore comparable with each other, but not with com- 
mercial linseed oils. 
The color was carefully noted in each case. Considerable diversity appeared, and 
the colors are described as well as possible in order to bring out the existing differ- 
ences. 
