DETECTION OF GELATIN. 



29 



It is not allowable to concentrate a solution by evaporation on a 

 steam bath, as caramel may be formed; if it is necessary to concentrate, 

 it must be done over sulphuric acid or at diminished pressure. 



In order to further identif}^ the color it is poured into a freshly 

 prepared solution of phenylhydrazin (2 parts phenylhydrazin-hydro- 

 chlorid, 3 parts sodium acetate, and 20 parts of water). The presence 

 of a considerable quantity of caramel gives a dark-brown precipitate 

 in the cold, hastened by heating a little. 



In the case of a very small amount it takes some hours for it to 

 collect. 



DETECTION OF GELATIN. 



The presence of gelatin in jellies and jams is shown b}^ a higher con- 

 tent of nitrogen. Precipitate a concentrated solution of jelly or jam 

 with 10 volumes of absolute alcohol and determine nitrogen in dried 

 precipitate b}^ the Gunning method.'*^ 



E. Beckmann ^' recommends the following method for the determina- 

 tion of gelatin in jellies: 



The jelly is treated with 95 per cent alcohol, the precipitate washed 

 with alcohol to remove all sugar, and the alcohol hnally removed by 

 heating. The residue is taken up with water and the extract is neu- 

 tralized with calcium carbonate and then treated with formalin. Upon 

 evaporation to dryness the gelatin is rendered insoluble. With pure 

 fruit jellies Beckmann found from 1 to 2 per cent of the precipitate 

 insoluble, while Avith jellies to which gelatin had been added TO to S6 

 per cent of the precipitate was found to be insoluble. 



DETECTION OF AGAR AGAR.'' 



Boil the jelly with 5 per cent sulphuric acid, add a crystal of potas- 

 sium permanganate, and allow to settle. If agar is present the sediment 

 will be rich in diatomes, which can be detected by use of microscope. 



Bomer gives the following anah^ses of two marmalades, one of which 

 contained agar and the other gelatin, which show how the addition of 

 these substances affects the different constants: 



Table 3. — Marmalade containing agar and gelatin. 



With agar . . . 

 With gelatin 



qr.iifl« [Insoluble .„, Pro- Acid as Invert Cane I p^ptin« Polariza- 



^^^^^- solids. ^^'^- tein. I malic, sugar. sugar, lectins. ^^^^ 



67.78 1.39 



70.96 1.31 i 



,74 



0.85 

 1.94 



1.26 

 1.23 



39. 32 

 43. 92 



19.60 



17. 86 



2.93 

 2. 52 



+3.64 

 + 1.27 



"^A. Bomer, Chem. Ztg., 1895, 19, 552. 



'' Forschungsberichte iiber Lebensmittel, 189(), 3, ?>27; Clieni. dor Nahr. iind 

 Genussmittel, 1896, 11, 378. 

 "G. Marpmann, Ztw^hr. angew. Mikrosk, 1896, 11, 257. 



