590 



FOODS AND FOOD ADULTERANTS. 



ent, and one by the addition of water only. The per cent, of carbonic 

 acid found in the latter estimation may properly be termed theavailabh 

 amount present in the powder, as it is the quantity which would be act- 

 ually liberated by the acid ingredient of the powder when it is used in 

 baking, and therefore represents the actual value of the powder for 

 aerating purposes, so tar as the evolution of gas is concerned. 



FIG. 26. 



For the determination of the total CO 2 the procedure was as follows : 

 Place in a short glass tube, the weight of which is known, about 1 to 2 

 grams of the sample, and weigh the whole as quickly as possible, the 

 amount taken being obtained by difference. The tube and contents are 

 gently dropped into the generating flask of the apparatus, which must 

 be perfectly dry. The flask is closed with the stopper carrying the tube 

 connecting with the absorption apparatus, and also the funnel tube, 

 which has been previously provided with 10 cubic centimeters of dilute 

 sulphuric acid for the liberation of the gas. When all parts of the ap- 

 paratus are connected, and seen to be tight, the stopper of the funnel 

 tube is opened, and the acid allowed to run slowly into the flask. The 

 generation of the gas should be, made as gradual as possible ; by run- 

 ning in a small quantity of the acid at first and tilting the flask slightly 

 this can readily be accomplished ; after the greater part of the sample 

 has been acted upon by the acid and before the latter has all been added, 



