174 METHODS OF ANALYSIS. 



From above follows : 



1 

 Volume of tubes and 



and 



G4-F 

 Volume of brass weights = . -=-. 



o.O 



G , F _G+F_ V 

 2.7" r 2.0 8.5 



representing the differential volume affected by temperature and pressure and 

 being a constant for the tubes. Now, 



T=VX0.0000039 gram, and 

 B=VX 0.0000015 gram. 



Observe that rise of temperature makes the air lighter, 'consequently th 



tubes heavier. Therefore the correction must be negative. On the other hand 



increased pressure has the opposite effect, making the correction positive. 



Example : 



G=80. F=40, from which follows 

 V=35.5, and 

 T=0.00014 gram, and 

 3=0.00005 gram. 

 Now, if 



A 1 =^26, 

 A 2 =270, 

 B 3 =759 mm, 

 B 4 =756 mm, 



then the correction for temperature will be 



0.00028 gram, - 

 and for air pressure 



0.00015 gram, 

 making a total of 



0.00043 gram. 



2. Residual Carbon Dioxid.o 



Weigh 2 grams of baking pmvder into ;i flask suitable for tho subsequeii 

 determination of carbonic acid, add 20 cc of cold water, and allow to stand 21 

 minutes. Place the flask in a metal drying cell surrounded by boiling wate 

 and heat, with occasional shaking, for 20 minutes. 



To complete the reaction and drive off the least traces of gas from the semi 

 solid mass, beat quickly to boiling and boil for 1 minute. Aspirate unti 

 the air in the flask is thoroughly changed, and determine the residual carbon 

 dioxid by absorption, as described, under total carbonic acid. 



The process described/* based on the methods of McGill & and Catling imi 

 tates as far as practicable the conditions encountered in baking but in such a 

 manner that concordant results may be readily obtained on the same sample 

 and comparable results on different samples. 



Conn. Agr. Exper. Stat., Kept., 1900, p. 100. 



6 Laboratory of the Inland Revenue Department, Ottawa, Canada, Bui. 68, p. 31. 

 Baking Powders : A Treatise on their Character, Method for Determination of 

 Values, etc., p. 20. 



