The Hydrogen-ion Concentration, etc., of Sea-Wateii'. 



43 



in the proportion of 10 mg. per liter. The burettes were protected with 

 soda-Ume tubes and the condensation water was mixed up by shaking 

 the burette occasionally. For this purpose a burette supported by 

 the stock bottle is most convenient, since connections are not damaged 

 in shaking. This burette is sometimes known as Squibb's automatic. 



12. — Test-tube gage and scale for 

 graduating the special gasometric ap- 

 paratus. The test-tube gage is to be 

 inserted in the test-tube. Its slope is 

 made very gradual in order to lessen 

 the error produced by incorrect esti- 

 mation of the position of the union of 

 thelip and cylindrical part of the tube. 

 It may be cut out and used immedi- 

 ately or after pasting it on a piece of 

 sheet metal of the same shape. In 

 using the other scale, find the position 

 at which the width of the scale is the 

 same as the length to be divided and 

 fold the scale parallel to the heavy line. 



A good glass as regards solubiUty is pyrex, but we have not become 

 skillful enough to use glass of so high a melting-point. On account of 

 its color Jena glass could not be used. The tubes used were nonsol 

 test-tubes of 24 mm. bore. We obtained a very large number of these 

 and divided them into grades in regard to bore, with the text-tube gage 

 shown in figure 12. Those of the same bore and the most nearly 

 cyhndrical were selected for a set. The measurements were verified 

 with a micrometer caliper, and no variation in any dianieter greater 

 than 0.2 mm. was allowed. Since there is danger of getting CO2 into 

 the tubes in sealing, they were first constricted in the middle to a very 



