Copyright © 1998 Richard A. Paselk
Beckmann's Freezing
Point apparatus-The fact that the temperature of an over-cooled
liquid rises to the freezing point when solidification occurs, has been
made the basis of a method of determining freezing points. Beckmann's apparatus
is shown in Fig. 77. It consists of a test tube A, provided with a side
inlet tube D, and a cork through which a thermometer T and a platinum wire
stirrer S2 pass. This test tube is surrounded by a larger tube
B, the space between the two forming an air jacket. Both are surrounded
by a larger vessel C, which call be filled with a suitable freezing mixture.
The latter is kept in circulation by means of the wire stirrer S1.
The method of using the above apparatus is as follows:-- Some of the
liquid of which the freezing point is required, is introduced ' 
into A, by way of the inlet tube D, which is afterwards closed by a
cork. A suitable freezing mixture is introduced into C, and the whole apparatus
is allowed to stand till the thermometer T indicates a temperature one
or two degrees below the probable freezing point of the liquid. The platinum
wire stirrer S2 is then moved briskly up and down, when solidification
will generally occur. The temperature indicated by T rises and shortly
attains a value which remains constant some time. This temperature is the
freezing point of the liquid.