BAKING POWDERS. 101 



H. TJ-tube filled with coarse calcium chlorid. 



K. Filled at I with a 3-inch long column of pumice stone impregnated with 



copper sulphate completely dehydrated at 150 C. The rest is filled with 



fine calcium chlorid. 



L. Cock to close the apparatus when not in use. 

 M. First absorption tube about one-half inch in diameter and 5 inches long, 



filled mainly with soda-lime, with a little calcium chlorid at the side at 



which the air current enters. 

 N. Second absorption tube of same size as M, filled half with soda-lime and half 



with calcium chlorid. Place the side containing calcium chlorid toward 



the end of the apparatus where the air current leaves. 



O. Guard-tube containing calcium chlorid toward N and soda-lime toward P. 

 P. Indicator tube trapped with glycerin. 



R. Safety bottle to receive water which may be sucked back from 

 S. The aspirator, which is a Mariotte's bottle of about 4 liters capacity. 



(2) Materials. 



Use calcium chlorid dehydrated at 200 C, 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. Prepare a large quantity of such 

 calcium chlorid at the beginning and use this for the tubes K, M, and N. The 

 reason for this is that the current of air must leave the weighed tubes with the same 

 content of moisture as it entered them, which only can be attained if the absorbent 

 in K and N is of the same nature and quality. 



The soda-lime* for the weighed tubes is ground and sifted in the same way. It 

 should not be too dry, as it must not absorb moisture to a higher degree than calcium 

 chlorid. The tubes M and N should hold about 20 grams filling each, making M's 

 capacity for carbon dioxid almost 1 gram and N's capacity for moisture 0.2 gram. 

 M should be refilled when its weight has increased 0.75 gram, and N after an increase 

 of 0.1 gram in weight. 



Use best rubber for all connections, applying a trace of castor oil as lubricator. 

 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. 



(3) Manipulation. 



Weigh M and N, taking precaution that they are of the same temperature as the 

 air in the balance-room. Shortly before weighing, open the tubes for a moment to 

 allow equalization of air. Note thermometer and barometer. Connect tubes with 

 the apparatus and make sure that all joints are tight by closing A at the bottom, 

 opening all cocks, starting the aspirator and observing P, in which the liquid must 

 soon come to a standstill. Then disconnect the aspirator, close B, remove F, put in 

 the substance b (use about 1 gram of sodium carbonate or calcium carbonate, or about 

 2 grams of baking powder), connect F, and start the cooler. Fill acid and water 

 through D, lifting E slightly and allowing only small quantities of the acid and 

 water to enter at the time. (Use only water made free from carbon dioxid by 

 boiling. ) Light the burner, heat to boiling, and reduce the flame to keep the liquid 

 just at the boiling point. If no more air passes P, start the aspiration. When 

 water stops running, open B carefully and adjust the outflow of the aspirator by 

 raising or lowering the syphon to half the safe speed. 



An excellent method for the preparation of soda-lime is given by Benedict and Turner, Jonr. 

 Amer. Chein. Hoc., 1K99, 21, 396. 

 'Set- Appendix, p. 167. 



