white: thermoelectric methods 321 



inserted or withdrawn at will without escape of air. The jacket 

 water surrounding the thermoelement above the cap insures defi- 

 nite conditions as to temperature. 



The best of these methods call for a complete inclosure by the 

 jacket, but this is almost indispensable in any calorimetry of 

 precision, and can be easily obtained. For instance, the calo- 

 rimeter chamber may be a cylindrical pot, suspended in a com- 

 mercial paper tub. The cover is a square box, filled with water, 

 and closed, save for two pipes which project downward thru the 

 surface of the water below and so provide for a complete circu- 

 lation. The protection against evaporation of the jacket water 

 which is usually necessary for precision work is very easily secured 

 by a layer of paraffin cast on the surface of the water. This 

 layer can of course be easily sawed or recast. By a suitable and 

 rather evident arrangement of thermoelements, any of these 

 schemes can be operated with the two calorimeters in two sepa- 

 rate jackets. This procedure is necessary in the case of adiabatic 

 methods. A precision of 0.0001° is very easily reached, under 

 fair conditions, with a thermoelement of 24 couples. Elements 

 of 8 couples, ordinarily precise to 0.0003°, are so very compact 

 that the use of anything smaller will rarely be advisable. 



Work with these methods has emphasized the desirability of 

 providing, not only abundant thennometric sensitiveness, but, 

 especially, a thoro and uniform jacket inclosure, with vigorous 

 stirring thru wide openings. The trouble required for these pre- 

 cautions is slight in itself, and is insignificant compared to that 

 likely to be entailed by trying to dispense with them. 



The requirements of these methods in the way of auxiliary 

 electrical apparatus (potentiometer, etc.) are unusually simple and 

 inexpensive, but are nevertheless exacting in certain directions. 

 Elaborate apparatus and methods, admirable for other kinds of 

 work, may fail here, tho success is easy by appropriate arrange- 

 ments. A revised account of the essential requirements is in 

 preparation. The great advantage of these methods is in the 

 ease and precision of the temperature measurement. Otherwise, 

 they present disadvantages, which, however, are evidently slight, 

 and far outweighed by the advantages. 



