BORON AND FLUORINE. 7 



of the Kipp generator is compressed by means of the stout rubber 

 bulb (a) and the stop-cock (6) closed. The empty bottle (c) 

 merely serves as a reservoir for the compressed air and communi- 

 cates with the mercury manometer (d), which also serves as a 

 safety valve. The bell-jar (e) is ground upon a glass plate and 

 covers the platinum dish (/) containing the sodium carbonate 

 solution. After the bell-jar has been filled with carbon dioxide 

 through the delivery tube (g) (which does not come in contact 

 with the solution) cylinder (h) may be filled with water to the 

 desired height. In the present instance an additional pressure of 

 only about 30 cm. of water was applied. This pressure, of course, 

 does not hasten the absorption of the gas very markedly, but as 

 the reaction was quite slow a slight acceleration was not unwel- 

 come. Even under the pressure applied, the upper reservoir 

 of the generator had to be wired to its base and the bell- 

 jar securely clamped to the plate. As practically no carbon 

 dioxide is wasted, the apparatus (when properly adjusted) will 

 run for days and requires little attention; it is advisable, of 

 course, to restore the original pressure occasionally by means 

 of the rubber bulb. 



The carbon dioxide was generated by the action of pure 

 hydrochloric acid on white marble. The gas passed through two 

 large towers; the first contained beads coated with moist sodium 

 bicarbonate, the other was similarly charged with moist silver 

 carbonate. Finally, before reaching the bell-jar, it was conducted 

 through two wash-bottles containing solutions of sodium bicar- 

 bonate. The contents of the platinum dish remained entirely 

 free from chloride. 



BORAX. 



Crystallized boric acid and sodium carbonate, prepared as 

 indicated in the preceding sections, were next brought together 

 by introducing small portions of the acid in solid form into a 

 boiling solution of the carbonate contained in a platinum dish, 

 until the boric acid was slightly in excess of the theoretical require- 

 ment for the formation of the tetraborate. Boiling of the clear 

 solution was continued until no more carbon dioxide was evolved. 

 The crystal meal, which separated out on cooling and stirring, 

 was drained on the platinum cones of a hand centrifugal and 



