28 
BULLETIN 1471, U. S. DEPARTMENT OF AGRICULTURE 
Table 19. — Percentages of linseed oil in a haloicax-linseed oil mixture made by 
adding 4 cubic centimeters (4-904 grams) of lialoicax oil to 2 grams of ground 
flaxseed containing 31, 31.1, 31.3, 31.5, 31.7, and 32 per cent of linseed oil 
Percentage 
of linseed oil 
in flaxseed 
sample 
Percentage 
of linseed oil 
in the halo- 
wax-linseed 
oil mixture 
31.0 
31.1 
31.3 
31.5 
31.7 
32.0 
11.224 
11. 256 
11. 320 
11.384 
11. 448 
11.544 
(3) In Table 18 it was shown that for every 1 per cent of linseed 
oil present in halowax oil the refractive index of halowax oil changed 
in a definite and regular manner. In the case of the experiments 
cited this change was 0.001906. All that is necessary, therefore, to 
express refractive index values in terms of the percentage of linseed 
oil present in ground flaxseed is to multiply each per cent and tenth 
of 1 per cent of linseed oil, as described in section 2 above, by the 
constant described under section 1. Finally, point off nine decimal 
places and subtract the value obtained from the refractive index 
of the halowax oil used in the tests. The results will appear like 
those in Table 20, which is the section of the scale usually used for 
flaxseed. 
(4) As is general with optical measurements, the temperature at 
which the readings are made is important. It is necessary when 
using this method to adjust individual readings to the same tem- 
perature basis. For general conditions 25° C. has been selected as 
an average laboratory temperature. Thus, for every degree above or 
below 25° C, 0.00045 is added to or subtracted from the original 
reading. This adjustment can not be overlooked, as this reading — 
0.00045 — is equivalent to approximately 0.75 per cent of oil. 
DETAILS OF METHOD FOR MAKING TEST 
(1) Grind 25 grams of the flaxseed sample so that at least 80 per 
cent of the meal will pass through a 34-grits gauze sieve. 
(2) Weigh out 2 grams of the ground sample and empty it into 
a 3-inch porcelain mortar, which has been previously heated to 70° C, 
and grind the flaxseed meal with 4 cubic centimeters of halowax 
oil, grade No. 1007, for at least two minutes. 
(3) Filter through a small folded filter, using a 40-millimeter 
glass funnel seated on a flat-bottomed test tube. 
(4) Let the tube and contents cool to room temperature. Place 
a drop of this mixture on the prism of the refractometer and take 
the average of three readings. 
(5) Note the temperature, and for every degree above 25° C. add 
0.00045 to the refractometer reading and for every degree below 
25° C. subtract this amount. 
