340 METHODS OF ANALYSIS [Chap. 



(B) is connected by means of a perforated stopper with a soda lime tube (C). The 

 upper end of the Liebig condenser is connected by a rubber joint with a Geissler 

 bulb (E), containing sulphuric acid for drying the gas passing into the next Geissler 

 bulb (F), connected with (E), and containing strong potassium hydroxid solution 

 (1 to 2). The bulb (F) is connected with a third Geissler bulb (G), containing sul- 

 phuric acid for the absorption of moisture escaping from F. A fourth Geissler 

 bulb {H) is attached to G as a precaution to prevent moisture from the air being 

 absorbed by G. H is connected with an aspirator. Many analysts prefer to re- 

 place the bulb (F) by 2 U-tubes filled with sifted soda lime. 



5 DETERMINATION. 



Place 0.5-2 grams of the baking powder, the amount depending upon the per- 

 centage of carbon dioxid present, in the flask (A), which must be perfectly dry. 

 Close the flask with the stopper which carries the funnel tube and the tube con- 

 necting with the absorption apparatus. Weigh separately the Geissler bulbs (F) 

 and ((?) and attach them to the apparatus. If 2 soda lime tubes are employed, 

 weigh them separately and fill the first anew when the second increases materially 

 in weight. Nearly fill the funnel tube (B) with hydrochloric acid (sp. gr. 1.1) and 

 place the soda lime tube (C) in position. Then aspirate air through the Geissler 

 bulbs at a rate of about 2 bubbles per second. Open the stopper of the funnel and 

 allow the acid to run slowly into the flask, care being taken that the evolution of 

 gas be so gradual as not to materially increase the current through the Geissler 

 bulbs. After all the acid has been introduced, close the stop-cock in B, continue 

 the aspiration and heat gradually the contents of the flask to boiling. While the 

 flask is being heated the aspirator tube may be removed, although many analysts 

 prefer, when using ground-glass joints, to aspirate during the entire operation. 

 Continue the boiling for a few minutes after the water has begun to condense in 

 D, then remove the flame, open the stop-cock in tube (B) and allow the apparatus 

 to cool with continued aspiration. Remove the absorption bulbs (F) and (G) and 

 weigh. The increase in weight is due to carbon dioxid. 



Method Using Heidenhain's Apparatus. — Tentative. 



6 REAGENTS. 



(a) Calcium chlorid.— Use calcium chlorid dehydrated at 200°C., but not fused. 

 Grind it coarsely in a coffee mill and sift through No. 18 wire gauze to remove the 

 extremely coarse, and through No. 30 wire gauze to remove the very fine, particles. 



(b) Soda lime. — Grind and sift the soda lime^ for the weighed tubes as described 

 above. It should not be too dry, as it must not absorb moisture to a greater degree 

 than the calcium chlorid. 



7 APPARATUS^. 



This consists of a cylinder (A), -filled with soda lime to remove carbon dioxid 

 from the air passing through the apparatus. A thick layer of cotton at the upper 

 end prevents soda lime dust from being carried over. Connect the cylinder (A) 

 by means of a perforated rubber stopper and a bent glass tube having a stop-cock 

 (B) and a capillary constriction (C) with a short piece of rubber tubing to which 

 is attached a short piece of glass tubing (£'), fitted with a perforated rubber stopper. 

 The latter fits tightly into the constriction of the funnel tube (D). The funnel of 

 the latter is cylindrical in shape, f inch in diameter at the upper end, f inch at the 

 lower end and 4 inches long, the rubber stopper of E fitting into the constriction. 



