BAKING POWDERS. 



99 



mentioned below are selected because the details have been carefully worked out by 

 the originators. 



According to the amount of absorbent employed the weight of sodium carbonate 

 or calcium carbonate may vary from 0.25 to 1.00 gram, and about twice as much 

 baking powder may be used. The corrections for temperature and pressure given 

 with the Heidenhain apparatus may ordinarily be disregarded. 



(a) KNORR'S APPARATUS. 

 (1) Description of apparatus. 



This apparatus (fig. 5) employs only ground -glass joints, and maybe quickly made 

 ready for use or taken to pieces and packed away. On the other hand, it is inflexible 



FIG. 5. Knurr's apparatus for the determination of carbon dioxid: A, Distilling flask fitted to con- 

 denser by a ground-glass stopper. H. Reservoir containing acid. C, Soda-lime tube fitted to acid 

 reservoir by a ground-glass s'topper. 1), Condenser. E, Liebi'g bulb filled with sulphuric acid. 

 F, Liebig bulb filled with a solution of potassium hydroxid for tin- absorption of carbon dioxid 

 and followed by a calcium-clilorid tube-. An additional guard tube filled with soda lime should 

 follow the tube F, though not shown in the cut. 



and must he -an 'fully handled, and has the additional disadvantage that broken 

 parts can not n-adily In- replaced. Therefore it is of more value for occasional 

 determinations than for a long series. :i 



The small calcium ehlorid tube shown in the cut attached to the potash bulb F is usually replaced 

 by a second Liebig bulb filled with sulphuric acid. Better results are obtained if the same drying 

 tubes aiv used before and after the potash bulb. Many analysts prefer to replace the bulb F and 

 attached calcium ehlorid tube by two U-tubes filled with sifted soda liine. When the second tube 

 shun - a material increase in weight it is placed first, and the first tube refilled and placed in the 

 second position. 



