1 66 TRANSPIRATION AND ASCENT OF SAP ch. 



supports the large test-tube which forms the freezing- 

 chamber. It is also perforated to admit a thermometer 

 into the freezing-bath and to allow the stirrer in the bath 

 to project from it. 



Details of procedure. To make an observation 

 with the apparatus say, to determine the freezing- 

 point of a solution the procedure is as follows : 

 the leads of the thermocouple are slipped through 

 the slit and the pine supports through the holes in 

 the upper cork bung, and the stop is fixed on one of 

 the supports above the cork, to prevent them falling 

 down. The freezing- chamber is then closed with the cork. 

 Meanwhile, two small test-tubes, one containing about 

 2 c.c. of the solution, and the other the same quantity of 

 distilled water, are being cooled by supporting them in 

 the freezing-bath, making use of the perforation in the lid 

 through which the stirrer works. 



When it is judged that they have reached their freezing- 

 point, a little hoar-frost is detached on a cooled platinum 

 needle from the outside of the freezing-chamber and intro- 

 duced into the distilled water. Ice crystals are immedi- 

 ately formed, and some adhere to the needle, which is 

 then transferred to the salt solution. Crystallisation is 

 instantaneously started in this, and the needle is with- 

 drawn. The two test-tubes are now put into the holes 

 of the smaller cork, and this is fixed on to the lower end of 

 the wire handle which passes down through the upper 

 cork, which has been removed from the freezing- 

 chamber momentarily for the purpose. The junctions on 

 the lower ends of the pine supports are now immersed in 

 the freezing liquids in the test-tubes. Thus arranged, the 

 whole, test-tubes and thermocouple, is put into the 

 freezing-chamber and the upper cork tightly adjusted. 



Stirring of the contents of the test-tubes is immediately 

 commenced by moving the pine rods up and down. As 

 these are rigidly connected together, the two test-tubes 



