14 MICRO-ANALYTICAL METHODS 



stream of water, washing out all of the starch. The gluten sepa- 

 rates out as a tenacious gummy mass. With care fairly accurate 

 quantitative results may be obtained. Weigh the dried flour 

 and compare with weight of the dried gluten mass. With cereal 

 flours other than wheat, the entire dough mass is gradually washed 

 away, leaving no gluten. 



10. Agar in Jams, Jellies and Similar Fruit Products. The 

 method generally recommended is to ash a sample of the jam or 

 jelly at as low a temperature as possible, and to add weak hydro- 

 chloric acid for the purpose of decomposing the carbonates, etc. 

 If agar has been added to the substance the silicious skeletons 

 of diatoms will appear in the ash residue examined under a com- 

 pound microscope. 



A far better method is to dissolve (with heat) about 10 grams 

 of the substance in 200 cc. of distilled water and centrifugalize 

 (while still hot) for half an hour. Decant off the supernatant 

 liquid and examine the residue microscopically. If agar has been 

 added, characteristic agar diatoms (mostly Arachnodiscus ehren- 

 bergii Baillon) will be found, also undissolved agar cell fragments 

 and remnants of undissolved parasitic algal forms, which are 

 quite universally found upon agar. The undissolved agar rem- 

 nants and the algal parasites, which are in fact almost as character- 

 istic as the diatoms, would be wholly destroyed by the ashing 

 process. Furthermore, the ashing-acid process, no matter how 

 carefully done, results in a comminution and destruction of some 

 of the diatom shells. Finding one or more diatoms and one or 

 more algal remnants in one slide mount (or in 5 to 20 fields of 

 view) is conclusive evidence that agar has been added, though 

 this does not indicate the exact amount that is present. If the 

 characteristic structures (diatoms and algal remnants) are com- 

 paratively abundant then it is safe to conclude that agar has been 

 added in considerable amount (24 per cent.) or that an impure 

 grade of agar was used. The purer the grade of agar the fewer 

 are the diatoms present, but no agar has yet been found on the 



