THE MACADAMIA NUT INB IWAI1 
7 
mined in a water-jacketed Abbe-Zeiss refractonieter, the temperature 
being maintained at 27.5° C. This refraetometer permitted direet 
reading to the third decimal place, the fourth place being estimated. 
The degree of accuracy is correspondingly less than that possible with 
an instrument of narrower range as used by Coleman and Fellows. 
The values for index of refraction (N D ) are plotted against corre- 
sponding percents of oil in the Halowax-oil mixtures in figure 2. The 
equation for the best fitting curve is (3) y= —497.1 l.r+806. 56 where 
7/ = the percent oil in the Halowax-oil mixtures and x=N D , the index 
of refraction. 
The curve in the above equation does not hold for all values of as 
proved by the fact that extrapolation of the equation to 2=1.4651, 
the index of refraction of pure macadamia-kernel oil, gives values for 
?/ of 78 percent instead 
of 100 percent, its true 
value. Within the lim- 
its used, x= 1.57 to 1.03, 
the true values of y 
follow the curve very 
closely. 
Using the relation- 
ship given in equation 
(3), the applicability 
of the refractive-index 
method to detennina- 
t LOU of the oil content 
of macadamia kernel 
was next studied. 
Kernels of the smooth- 
shell type Were sepa- 
rated by Specific grav- 
ity into 7 samples, each 
containing 1 2 to 15 
kernels. Each sample 
was t h e n fi n el y 
chopped and thorough- 
ly mi xed. E t h e r- 
ex tract determina- 
tions wei / made as de- 
scribed under specific gravity. In determining the refractive index, 5 
ml of Halowax were measured exactly as in the procedure described in 
the foregoing section and added to a weighed portion of the kernel in a 
small porcelain mortar. The mixture was I hen triturated with a pestle 
for about 10 minutes. A drop of liquid was withdrawn and the refrac- 
tive index determined. Trituration was then continued until a con- 
stant reading resulted. For the final reading, a portion of the liquid 
was passed through filter paper. N D determinations were made in trip- 
licate and ether extract in duplicate. The results are given in table 3. 
£ 30 
INDEX OF REFRACTION 
Figlrk 2.— Index of refraction of mixtures of maeadamia nut oil and 
Halowax in varying proportions. 
