42 University of California Publications in Zoology [Vol. 13 



The same principle of heating and regulation may be applied to 

 any other apparatus requiring a uniform temperature, there being 

 liquids obtainable boiling at practically any desired degree of tempera- 

 ture. Where the temperature desired is very low the condensing tube 

 would have to be water-cooled, but for paraffin an air-cooled tube is 

 adequate. The amount of cooling surface required for regulation 

 would vary as the degree of uniformity of the source of heat employed. 

 We have used for two years a large copper paraffin bath (30 cm. X 

 30 cm. X 10 cm. ) heated with gas and regulated in the same manner 

 by chloroform vapor. Our gas pressure is exceedingly variable and 

 about three meters of brass tubing was found to be necessary to pro- 

 vide for the extreme variation. With the electric bulb of the small 

 bath here described thirty centimeters seems to be ample, the appa- 

 ratus as figured having a tube nearly three times as long as our ex- 

 perience has shown to be necessary under our rather uniform room 

 temperature. 



The advantages of this new form of bath are : 



1. Simplicity, the bath requiring no adjustment and having no mechanical 

 apparatus to get out of order. 



2. Precision of regulation, since no variation of temperature in the heat- 



ing medium occurs such as is necessary in an apparatus with a mechani- 

 cal thermostat. 



3. Illumination of cup, a convenience in handling the object in filtrating 

 and an aid in keeping the cup clean. 



4. Inexpensiveness, the cost of the whole equipment being not over two 



dollars and a half. 

 0. Safety, the heat being by electric lamp, and the regulating fluid being 

 non-inflammable. 



Transmitted January IS, 1914. 



