544 
Journal of Agricultural Research 
Vol. XXI, No. 8 
the escape of the more volatile constituent the boiling point of the residue 
is increased. The boiling point of the liquid used as a heating medium 
should be frequently tested, particularly when mixtures are used, in 
order to guard against any change. For this purpose it is advisable to 
have some provision made by which a thermometer may be inserted into 
the flask, F. 
SPECIFICATIONS FOR APPARATUS 
The kettle described was constructed as a laboratory model. For 
practical purposes the following general specifications are suggested: 
(1) Size. A kettle larger than io by 20 inches should not be con¬ 
structed until its feasibility has been demonstrated. The smaller the 
diameter of the kettle the greater is the heat-absorbing surface obtained. 
On this account the diameter should not exceed one-half the height. 
With small diameters there is a rapid flow of convection currents, and 
it may be possible to abolish the mechanical stirrer. 
(2) Construction. The kettle should be constructed of a noncorrosive 
metal, without crevices, seams, or comers that can not be readily cleaned. 
The advantages derived from this kettle are: (1) It is of simple con¬ 
struction, (2) is entirely automatic, (3) there is no danger of overheating, 
(4) any desired temperature is obtained by using a liquid of suitable 
boiling point, and (5) a minimum of a fluid, which may be expensive, is 
used to maintain a maximum of another fluid at a predetermined 
temperature. 
With these advantages it is believed that the usefulness of this kettle 
will not be limited to the heating of clear hog-cholera serum but that it 
can be used for heating various serums and vaccines, or it may be 
used for any purpose in which a constant-temperature bath is necessary. 
