13 



the laboratory. After removal of the foliage from the stems, they were 

 broken at the nodes and placed in hard glass test tubes (25 mm. X 150 

 mm.), stoppered with rubber stoppers and sealed with oil paper and rub- 

 ber bands. Freezing was produced by the use of the ice and salt bath,* 

 giving a temperature of —15° or lower and allowing the tubes to remain 

 in the refrigerator overnight. The tubes were then removed from the bath 

 and after the walls had been cleaned with distilled water and wiped dry, 

 the portions of shoots were removed, thawed gradually, and the sap ex- 

 pressed by pressure from the screw of a tincture press set perpendicular 

 to the wall upon two pieces of Vs inch plate glass. After a first expression, 

 the shoots were rearranged and pressure again applied. The sap was 

 filtered through an S. & S. 589 filter — with a watch glass over the funnel 

 to minimize evaporation — into a small test tube; a drop of xylene was 

 added as a preservative and the tubes placed at once in a refrigerator, at 

 about 10°. The sap after filtration was usually a clear, brown liquid 

 without sediment. 



As soon as convenient the freezing-point determinations were made. 

 A thermometer was used having a bulb about 5 mm. by 35 mm., the mer- 

 cury tube enclosed in a hollow jacket, and graduated to — 6 . 5 ° in tenths 

 of degrees, upon which, by the aid of a lens, hundredths of a degree could 

 be read without danger from parallax. A stirrer of platinum wire and 

 the thermometer were placed in the 5 cc. of sap contained in a test tube 

 of Bohemian glass (15 X 120 mm.) and the whole cooled to about +2° 

 in an ice and salt bath in a beaker. The tube was wiped free from water 

 and placed within a hard glass test tube (25 mm. X 150 mm.) set two- 

 thirds way into the ice and salt-freezing mixture. It was found saving 

 of time to place this bath in a Dewar bulb, with inside diameter of 35 X 

 130 mm.; the top was closed with a piece of cork; the bath so arranged 

 remaining efi"ective for three hours or more of use. During the entire 

 cooling, the sap was constantly stirred to prevent its freezing about the 

 sides of the tube. The lowest temperature obtained was read to one- 

 tenth, and the maximum, by the aid of a lens, to one-hundredth degree. 

 The tube was removed to a beaker of water, and after the temperature 

 had risen to about 10°, the determination duplicated to within 0.01°, 

 usually without difficulty on the first trial. A typical determination 

 gave the following values: 



A' = 1.28 « = 4.12 A = 1. 214 



A' = 1.27 « = 3.43 A = 1. 216 



Average 1.2 15 from which tt = 14.64 atmospheres. 



* It was found cShvenient in case less than a dozen tubes of material were frozen' 



to place the ice and salt bath in one or two one-liter Jena beakers. In this way the 



ice can be packed about the upper portions of the test tubes, and the beakers, with fiYC 



or six test tubes in them, are narrow enough to keep the tops of the test tubes from 



touching the solution. 



