g. to get its weight:
10?1.2 = 12 15?1.5 = 22.5
add these together (12+22.5 = 34.5) and divide by the sum of the volumes
(10+15 = 25):
25)34.5(1.38
25
--
95, &c.
The sp. g. will be 1.38, provided the mixture is not accompanied by any
change of volume.
The same formula will serve when the proportion of the ingredients is
given by weight. A mixture of 4 parts by weight of galena (sp. g. 7.5)
with 5 parts of blende (sp. g. 4) will have a sp. g. of 5.06:
sp. g. = (4+5)/(0.53+1.25) = 9/1.78 = 5.06
It is necessary in this case to calculate the volumes of the galena and
of the blende, which is done by dividing the weights by the sp.
gravities: thus, 4 divided by 7.5 gives 0.53 and 5 divided by 4 gives
1.25.
The converse problem is a little more difficult. Given the sp. g. of a
mixture and of each of the two ingredients, the percentage by weight of
the heavier ingredient may be ascertained by the following rule, which
is best expressed as a formula. There are three sp. gravities given; if
the highest be written H, the lowest L and that of the mixture M, then:
Percentage of heavier mineral = (100?H?(M-L))/(M?(H-L))
Suppose a sample of tailings has a sp. g. of 3.0, and is made up of
quartz (sp. g. 2.6) and pyrites (sp. g. 5.1): then the percentage of
pyrites is 27:
(100?5.
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