EXAMINATION OF VINEGAE. 209 



in the latter entering the flask through the tube L. The burette 

 being emptied by the discharge of the fluid through Q 19 it is re- 

 filled for another determination of acid by simply pressing on Q, 

 and this can be repeated as long as the flask contains soda solu- 

 tion. 



In discharging the fluid from the burette by opening Q v air 

 from the outside passes into the apparatus through A. In doing 

 so it must, however, pass through the line which fixes the car- 

 bonic acid contained in it, so that the fluid in the flask remains 

 free from carbonic acid even after standing for months. 



The calculation of the quantity of acetic acid present in 

 the vinegar examined is made as shown by the following ex- 

 ample : 



For 10 cubic centimetres of vinegar were consumed 70 cubic 

 centimetres of decinormal soda solution. 



One cubic centimetre of decinormal soda solution being equal 

 to 0.006 gramme of acetic acid, hence 70 cubic centimetres 

 0.42 gramme. 



Now, as 10 cubic centimetres contain 0.42 gramme of acetic 

 acid, 100 cubic centimetres contain 10 times 0.42 gramme 4.2 

 grammes of acetic acid; or the vinegar examined contains 4.2 per 

 cent, by weight of acetic acid. 



CHAPTER XX. 



EXAMINATION OF VINEGAR AS TO THE PRESENCE OF FOR- 

 EIGN ACIDS AND OF METALS, AS WELL AS TO ITS DERIVA- 

 TION. 



Detection of Acids. 



SOME unscrupulous manufacturers, in order to pass off weak 

 or inferior vinegars, adulterate them with mineral acids. Such 

 adulteration is not only a fraud, but dangerous to health, and it 

 is necessary to indicate the means by which such additions can 

 be detected. 

 14 



