8 
BULLETIN 79, HAWAII EXPERIMENT STATION 
Table 3.— Comparison of percent of oil by refractive index method with percent ether 
extract in macadamia kernels 
Weight of sample (grams) 
Index of re- 
fraction at 
27.5° C. 
Proportion 
of oil in 
Halowax- 
oil mixture 
Proportion of oil in kernel 
Calculat e f i 
from equa- 
tion i 
Ether ex- 
tract 
-L'G V Id LIU 11 
of calcu- 
lated value 
from ether 
extract 
2 0473 
1. 5899 
1. 5902 
1. 5909 
Percent 
21.438 
21. 325 
20. 916 
Percent 
80. 77 
80. 55 
80. 10 
Percent 
Percent 
2 0403 
2.0022 
77. 26 
Average. 
80. 47 
77. 26 
+3. 21 
2 1076 
1. 5899 
1. 5907 
1. 5912 
21. 428 
21.019 
20. 763 
78. 45 
78. 85 
78.29 
2 0464 
73.76 
74. 84 
2.0294 
Average.. .. 
78. 53 
74. 30 
+4.23 
2 1728 
1. 5909 
1. 5902 
1. 5895 
20.916 
21. 274 
21. 632 
73. 81 
74. 38 
74. 70 
9 9097 
71.28 
70. 41 
2.2405 
Average 
74. 30 
70. 85 
+3. 45 
O 071 1 
1.5919 
1.5911 
1. 5893 
20. 405 
20.814 
21. 734 
75. 04 
75.23 
74. 68 
9 1 1fi/1 
70. 97 
71. 27 
2.2546 
Average 
74. 98 
71. 12 
+3. 86 
2 1647 
1. 5918 
1. 5930 
1. 5936 
20. 456 
19. 843 
19. 536 
72.03 
73. 19 
72.61 
68. 78 
66. 87 
2.0273 
Average 
72.61 
67.83 
+4. 78 
2.0438 
1. 5958 
1.5940 
1. 5908 
18.411 
19. 332 
20. 968 
2.1495 
67. 60 
67.60 
66. 12 
66. 51 
2.3798 
Average 
67. 38 
66. 32 
+ 1.06 
2.1546 
1. 5961 
1.5949 
1.5917 
18. 258 
18. 871 
20. 507 
62. 86 
62. 35 
62.81 
2.2618 
61.23 
61.03 
2.4903 
62. 67 
61. 13 
+1. 54 
i Equation (3) p. 7. 
Table 3 shows the results by the refractometer method to be con- 
sistently higher than those by the ether-extract method, due probably 
to the solution of substances other than oil which affect the refractive 
index. The close agreement of triplicate results indicates that the 
refractive-index method of determining the oil content of macadamia 
nuts is essentially accurate if proper corrections of the curve are made 
In fact, the differences between determinations are less in most in- 
stances than those by the ether-extract method. 
For the present purpose the refractometer method has little to 
commend it as compared with the specific-gravity method. Ii is 
much more cumbersome and requires relatively expensive equipmenl 
Moreover, with the specific-gravity method, the kernels are unaffected 
so that direct correlation may be had with other characteristics such 
as chemical composition, roasting qualities, and the like. 
