XXVIII] 



BAKING POWDERS 



341 



The stem of the funnel tube (/)) passes through a doubly perforated rubber stopper 

 almost to the bottom of the evolution flask (F), which is ordinarily of 150 cc. 

 capacity but, in the case of foaming liquids, may hold 300 cc. Through the second 

 perforation in the stopper connect the evolution flask (F) with a reflux condenser 

 (G), consisting of a j inch glass tube around which is wound a small lead pipe carry- 

 ing a current of cold water. To the upper end of the condenser attach a U-tube 

 containing a little calciimi chlorid (to be renewed when it has liquefied) to retain the 

 bulk of the moisture. Connect this U-tube with a second U-tube (//), filled with 

 coarse calcium chlorid, and this in turn with a third U-tube (K), filled at / with a 3 

 inch column of pumice stone impregnated with copper sulphate and completely de- 

 hydrated at 150°C., the remainder of the tube being filled \vith fine calcium chlorid. 

 Connect the U-tube (K) with a bent glass tube having a stop-cock (L) which is 

 closed when the apparatus is not in use. Next attach the absorption U-tubes (M) 

 and (iV) which are | inch in diameter and 5 inches long, the first filled mainly with 

 soda lime but containing a little calcium chlorid at the end where the air current 



FIG. 15. HEIDENHAIN'S APPARATUS FOR THE DETERMIN.VTION OF 

 CARBON DIOXID. 



enters, the second filled one half with soda lime and one half with calcium chlorid, 

 the latter being placed at the side where the air current leaves. Connect A'' with 

 a guard tube (0), filled with calcium chlorid on the side toward A^ and with soda 

 lime on the side toward P, the latter being a small U-tube trapped with glycerol to 

 indicate the passage of the air current. Connect P with a safety bottle (R), to 

 receive any water which may be sucked back from the aspirator, and connect R 

 with the aspirator (S), a 4 liter Mariette bottle. 



The tubes (M) and (N) should hold about 20 grams, making the capacity of M 

 for carbon dioxid almost 1 gram and that of N for moisture 0.2 gram. M should 

 be refilled when its weight has increased 0.75 gram and A'' after an increase of 0.1 

 gram in weight. 



Use the best grade of rubber for all connections, applying a trace of castor oil 

 as a lubricant. For connections of the weighed tubes use rubber tubing boiled in 

 weak lye, washed and dried. Apply also a little castor oil, which is thoroughly 

 wiped off again before connecting the tubing. 



Before using the apparatus fill H and K with carbon dioxid in order to saturate 

 the alkalinity of the calcium chlorid and exhaust after several hours. 



