4 
BULLETIN 70. HAWAII EXPERIMENT STATION 
chemical composition and quality has been used with a variety of 
products, for example, to show the starch content of potatoes (4), 
and the sugar content and maturity of prunes (6). 
SPECIFIC GRAVITY 
The macadamia kernel lends itself well to specific-gravity measure- 
ment, a single nut being of sufficient size to permit individual deter- 
mination if desired. 
The specific-gravity method, as finally perfected for the macadamia, 
was as follows: The kernel was suspended by forcing into it a fine steel 
wire of about 30 gage (Brown & Sharpe). To insure that there were 
no air spaces between the halves, the kernel was split and the halves 
were strung on the wire with the convex surface downward. The 
macadamia kernel is of such tender texture that the wire penetrates 
without difficulty and with a negligible rupturing of tissue. One end 
of the wire was bent into a hook and the nut was suspended on an 
ordinary analytical balance. It was weighed in air, and then im- 
mersed in ethyl alcohol of about 95 percent or any other convenient 
strength. Ethyl alcohol was found to be satisfactory for the purpose. 
Its specific gravity of 0.8092 (95 percent by volume at 25°/25° C.) is 
sufficiently less than that of the lightest macadamia kernel (about 
0.965) to permit accurate determinations. Imbibition or interaction 
of nut and alcohol is negligible as judged by the fact that the weight 
of the kernel remains practically constant during the time required 
for weighing in alcohol. The volume of that portion of the steel wire 
which is submerged is a constant factor and too slight to be of conse- 
quence. The specific gravity of the alcohol solution was checked at 
intervals during the tests and frequent measurements of temperatures 
were made for intermediate corrections. 
The kernel, after specific-gravity determination, was wiped dry and 
placed in a stream of air at 60° to 70° C. for about 1 hour to remove the 
last traces of liquid adhering. The oil was then determined by ether 
extraction in a Soxhlet apparatus for 24 hours. The procedure finally 
adopted was as follows: The kernel was placed on a 7-cm filter paper 
and shaved very fine with a sharp knife or razor blade. The filter 
paper and contents were placed in an alundum thimble and extracted 
in a Soxhlet apparatus overnight. The kernel was then ground in an 
agate mortar. Sufficient oil had been extracted so that the material 
could be ground to a fine powder. It was then replaced in the filter 
paper and alundum thimble and extraction continued for the re- 
mainder of the 24-hour period. The oil was dried to constant weight 
at 100°. 
Specific-gravity determination has many desirable features as a 
laboratory method. It is very rapid and requires no special laboratory 
equipment. The determination of the specific gravity of a single 
kernel is often of great advantage. The kernel can subsequently 
be used for determination of oil, sugars, roasting qualities, or any 
other properties that it is desired to measure. Use of the entire 
kernel for ether-extract determination simplifies the procedure and 
increases its accuracy since exact sampling of the ground kernel is 
exceedingly difficult. 
Table 2 gives the results of specific-gravity and ether-extract 
determinations on a series of 34 rough-shell and GO smooth-shell 
kernels, the nuts being selected at random from commercial samples. 
