The sirup gauge is a graduated glass tube, with a weighted bulb, that
registers from 0° to 50°, and that is employed to determine the quantity
of sugar contained in a sirup.
If this gauge is placed in pure water the bulb will rest on the bottom
of the cylinder or other container. If sugar be dissolved in the water
the gauge will begin to float. The more sugar there is dissolved in the
water the higher the gauge will rise. In making tests it is essential
that the sirup should be deep enough to reach the zero point of the
gauge. If a glass cylinder holding about half a gill is filled to about
two-thirds its height, and the gauge is then placed in the cylinder, the
quantity of sugar in the sirup will be registered on the gauge.
Experiments have demonstrated that when sugar is dissolved and heated in
fruit juice, if the sirup gauge registers 25°, the proportion of sugar
is exactly right for combining with the pectin bodies to make jelly. The
sirup gauge and the glass cylinder must both be heated gradually that
the hot sirup may not break them. If the gauge registers more than 25°,
add a little more fruit juice. If, on the other hand, it registers less
than 25°, add more sugar. In making sirups for canning and preserving
fruits, the exact amount of sugar in a sirup may be ascertained at any
stage of boiling, and the sirup be made heavier by adding sugar, or
lighter by adding water, as the case demands.