100 PROVISIONAL METHODS FOR ANALYSIS OF FOODS. 



(2) Materials. 



The potassium hydroxid solution usually employed for absorbing carbon dioxid 

 has a specific gravity of about 1.27. Many analysts, however, prefer a solution 

 naving a specific gravity of 1.55. 



The calcium chlorid and soda lime employed should be finely granulated and 

 freed from dust with a sieve. 



(3) Manipulation. 



The quantity of baking powder to be examined is placed in a distilling flask, 

 which must be perfectly dry. a The flask is closed with a stopper carrying the 

 tube connecting with the absorption apparatus and also with the funnel tube. The 

 tubes in which the carbon dioxid is to be absorbed are weighed and attached to the 

 apparatus. In case two Liebig bulbs are employed, one for potassium hydroxid and 

 the other for sulphuric acid, to absorb the moisture given up by the potassium hydroxid 

 solution, it will be necessary to weigh them separately. If two soda-lime tubes are 

 employed it will be found advantageous to weigh them separately and fill the first tube 

 anew when the second tube begins to increase in weight materially. The tube B is 

 nearly filled with hydrochloric acid (sp. gr. 1.1), and the guard tube C placed in 

 position. The aspirator is now started at such a rate that the air passes through the 

 Liebig bulbs at the rate of about two bubbles per second. The stopper of the funnel 

 tube is opened and the acid allowed to run slowly into the flask, care being taken that 

 the evolution of gas shall be so gradual as not to materially increase the current through 

 the Liebig bulb. After the acid has all been introduced, the aspiration is continued, 

 when the contents of the flask are gradually heated to boiling, the bulb in tube B 

 being closed. 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. The boiling is continued for a few minutes after the water has 

 begun to condense in D, when the flame is removed, the valve in the tube B opened, 

 and the apparatus allowed to cool with continued aspiration. The absorption tubes 

 are then removed and weighed, the increase in weight being due to carbon dioxid. 



(b) HEIDENHAIN'S APPARATUS. 

 (1) The apparatus. 



This was originated by G. J. Mulder and recommended and improved by 

 Kolbe, Stolba, and Fresenius, b and has been modified by H. Heidenhain, c as shown 

 in Fig. 6, which is drawn on a scale of 1 : 12. It consists of 



A. A cylinder filled with soda-lime to free the air from carbon dioxid. A thick 



layer of cotton prevents soda-lime dust from being carried over. 



B. Glass cock to regulate the air current, which finds resistance at C. 



C. A capillary contraction. 



D. Funnel tube of peculiar shape. The funnel is cylindrical, three-fourths of 



an inch wide and 4 inches long, and is reduced to half its width at the 

 bottom, so as to make a neck for a perforated rubber stopper into which 



E. A glass tube is tightly fitted, allowing the stopper to be taken out and put in 



by the glass tube. 



F. Evolution flask, ordinarily of 150-cc capacity, for foaming liquids of 300-cc 



capacity. 



G. Return condenser, simply a glass tube of one-foarth of an inch bore, around 



which a small lead pipe is wound. The tube following the condenser con- 

 tains a few pieces of calcium chlorid, to retain the bulk of the moisture. 

 It is refilled when contents are liquefied. 



Sec Appendix, p. 157. 



> Quant. Anal., vol, 1, p. 449, and vol. 2, p. 308, German edition. 



c Jour. Am. Chem. Soc., 1896, 18, 1. 



