251 



Test No. 2. — The number of grams to separate the disk from water 

 at 7° C. 



Trial 1 48.710 



Trial 2 48 . 715 



Trial 3 48.725 



Trial 4 48.730 



Average 48 . 720 



Test No. 3. — The number of grams to separate the disk from water 

 at 7° C. • 



Trial 1 48 . 630 



Trial 2 48.640 



Trial 3 48 .655 



Trial 4 48.675 



Average 48 . 650 



The diameter of the disk being 10.6898 cm., the radius being 5.3449 

 em., the area is S9.7200 square cm. In the first test given above it required 

 0.5431 g. to separate one square cm. of water. In the second 0.5430 g. 

 and in the third 0.5421 g. The average of the three tests is 0.5427 g. per 

 square cm., which is equal to 531.840 dynes per square cm. 



In comparing these results with those of Gay-Lussac we find that he 

 used a disk which was 11.86 cm. in diameter, and that it required 49.40 g. 

 to separate the disk from water, or 526.875 dynes per square cm. 



At this point it may be well to state the precautions taken in the ex- 

 periment. First, in order to insure that the water used was chemically 

 pure, ordinary laboratory distilled water was redistilled in Jena glass 

 vessels in the presence of sulphuric acid and potassium dichromate. Sec- 

 ond, the disk was thoroughly cleansed by washing in a solution of po- 

 tassium dichromate and sulphuric acid ; then in alcohol ; then the disk 

 was dried in a current of air and washed again in redistilled water. Third, 

 a delicate laboratory balance with a rider weight was used in the experi- 

 ment. 



At the time the above data on the cohesion of water was worked out 

 it was suggested that certain dissolved salts have a marked effect upon 

 the cohesion of water. It is the purpose now to note some of these effects. 



A number of solutions of certain salts in distilled water have been 

 tested by means of the same glass disk as used in the cohesion of water 

 experiment. The first solution tested was that of sodium chloride. Six 



