202 



PHYSIOLOGY OF NUTRITION. 



anthracite coal, are very suitable, while for larger rooms (above 

 150 cubic metres in capacity) the larger forms of Meidinger 

 stoves are to be recommended. Pfeffer 2 using such stoves suc- 

 ceeded in keeping the variations of temperature, at table height 

 and at some distance from the window, within 0'18 C. for days 

 and weeks. 



To expose plants for a considerable time to a temperature of 

 C., we employ the ice-chest described in 49. Places of very 

 constant low temperature, above C., are deeply situated cellars, 



ice-cellars, and even rooms 

 facing the north in a building 

 with thick walls. 



Good thermostats are of very 

 special importance in many 

 physiological researches, e.g. in 

 many experiments relating to 

 root pressure. They are to be 

 obtained, e.g., from Dr. H. 

 Rohrbeck, Berlin. (See Ap- 

 pendix.) No. 114 in Rohrbeck's 

 1891-2 price list is very good ; 

 price according to size, 50200 

 mks. A simpler, but still very 

 serviceable thermostat is No. 

 129 ; price according to size, 

 20-30 mks. This thermostat is 

 double walled, provided with a 

 water-level gauge and tap, and 

 mounted on a tripod ; it has a 

 glass cover, which may be re- 

 placed by a bell-glass, and is 

 completely lined with felt. It 

 is best to have it provided 

 with a ventilating arrangement. 

 The apparatus is represented 

 in Fig. 76. Gas pressure 

 regulators, gas-burners, e.g. 

 the convenient micro-burner 



for very small flames and thermo-regulators are also to be ob- 

 tained from Rohrbeck. No. 149 is a regulator which, filled and 

 tested, costs 19 mks. The head of this efficient regulator is made 



FIG. 76. Thermostat, with thermo-regu- 

 lator. 



