FOOD 579 



Sulplnirous Acids and Sulphites. 



The preservative may be present as acid sulphites of sodium or 

 calcium or as sulphur dioxide gas itself. This is the case especially 

 in wines or molasses where the acids are present probably partly in 

 combination with aldehydes and sugars. 



Weigh 50 grm. of sample into a 500 c.c. flask. 



If a solid, add recently boiled water. 



Through the separatory funnel of the flask add 5 to 10 c.c. of a 

 20 per cent, solution of phosphoric acid. 



Distil by steam in a current of carbon dioxide, collecting the distil- 

 late in 25 c.c. of saturated bromine water. 



Distil about 150 c.c. adding a little more bromine water if necessary. 



After distillation is complete boil off the excess of bromine. 



Dilute the solution to 250 c.c. 



Add 5 c.c. of hydrochloric acid. 



Heat to boiling. 



Add very slowly, with constant stirring, a hot 10 per cent, solution 

 of barium chloride, until in slight excess. 



Allow to stand for an hour, filter, wash with hot Avater, ignite and 

 weigh as barium sulphate. 



A " blank " experiment should be done without any of the sample 

 in the flask and any barium sulphate obtained subtracted from the 

 main amount. 



A special work should be consulted for this more technical test for 

 which special apparatus is necessary. 



Fluorides. 



The fluorides of sodium and ammonia have been used more 

 especially in beer and malt extracts. 



The etching of glass method is the best for detection. 



See a special work for this more technical test. 



Saccharin. 



It has some antiseptic power but it is generally employed as a 

 sweetener. The continued use of small quantities, say of 0*3 grm. per 

 diem, is sufUcient to impair the digestion. 



Extract wdth ether as for benzoic acid. 



Evaporate spontaneously and taste the residue. 



A sweet taste is positive for saccharin to 20 mg. per litre. 



If present a more complicated test should be carried out to get rid 

 of any " false saccharin " which may be present. 



Copper Sulphate. 



Make an ordinarv watery solution. 



Add ammonium sulphide. 



A black colour is positive for copper sulphate (and lead). 



The colour is not discharged by acids. 



