I have offered the information below on creme of tartar in the past -
two years ago or more. The information on making hard candy is new here.
It is from an old handout of mine. The recipe is imprecise as to amount
of sugar. I haven't made it in a while but  I think 10 pounds per quart
of water is a good starting point.

Dick Bonney
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HARD CANDY FOR WINTER FEED

Ingredients - granulated sugar and water.

        For a couple of hives, bring  a quart of water to a near boil. Turn off
the heat and add as much sugar as will dissolve in the water. Then bring
to a full boil, stirring constantly. Take care not to scorch this
mixture. Boil for at least thirty minutes, perhaps longer. Test for the
soft crack stage by using a candy thermometer. Temperature should be
about 275° - 280° F.
        In the absence of a thermometer, drop a little of the candy into ice
water. When done, the mixture should form hard threads in the water,
bendable but not brittle.
        When the candy has reached the proper temperature, pour out onto wax
paper, forming a sheet about one quarter inch thick. After it has
started to harden, score the surface to aid in breaking the candy into
pieces.
        The finished color should be a light amber. If it is appreciably darker
it may be scorched. Scorched candy will kill bees.
        To use, lay pieces of this candy on top of the frames, over or very
close to the brood area. An alternate method is to pour the candy onto
the rimmed side of a spare inner cover, instead of onto waxed paper.
This cover can then be inverted and placed on the hive over the brood.

Using Cream of Tartar.

        A part of the normal process when bees convert nectar to honey in the
hive involves the chemical inversion of sugar. Simply stated, sucrose is
converted to glucose and fructose.
        When we feed bees sugar syrup, they make a similar inversion. The
standard feed, granulated sugar, is sucrose. The bees convert this to
glucose and fructose before storing it.
        It has long been the practice of many beekeepers to add tartaric acid
to sugar syrup to aid in the inversion process, and instructions for
making syrup often call for tartaric acid, either as such, or in the
form of cream of tartar. The acid also prevents crystallization of the
syrup later.
        Many years ago a researcher (Leslie Bailey) found that if no natural
nectar was coming in, feeding syrup containing cream of tartar (or
vinegar) caused dysentery, shortening the lives of the bees to one third
that of bees fed plain sugar syrup. This finding was written up at the
time but does not seem to have become part of the common knowledge of
beekeepers. Tartaric acid is still occasionally recommended, without any
qualification as to the possible ill effects. Use it judiciously if at
all.