METHODS OF ANALYSIS. 37 



tin were very irregular and inaccurate, and in all cases only a portion 

 of the gelatin added was recovered. It is evident that the presence 

 of albumoses and peptones, as well as of gelatoses and gelatin peptones, 

 tends to dissolve the gelatin and give low results by this method. 



The Beckmann formaldehyde method," together with some com- 

 ments thereon, reads as follows: 



A method for the estimation of gelatin in meat extracts is based upon the fact that 

 formaldehyde combines with it to form a nonfusible and insoluble compound — 

 formalin-gelatin. In order to render insoluble 1 gram of gelatin dissolved in water 

 about two drops of the 40 per cent solution in water of formaldehyde (formalin) are 

 added. The quantity required is so trifling that its weight may be neglected. 



The presence of much free acid hinders the reaction, which, however, takes place 

 perfectly well in a slightly alkaline solution. * * * If formic or acetic acid be 

 present, either too little precipitate is obtained or none at all. * * * Soluble 

 egg-albumin and serum albumin left residues on mixing with formalin. * * * 

 Merck's dry peptone was found to be completely soluble in the presence of formalin, 

 and by this means gelatin and albumin could be easily separated from peptone. * * * 



In determining whether a meat extract contains gelatin, the albumin is estimated 

 in an aliquot part of a watery solution by means of acid. Another portion is treated 

 with formalin, steamed on the water bath, and, after boiling for a short time with 

 water, the residue is collected in a Gooch crucible, dried at 100° C, and weighed. 

 After subtracting the amount of albumin previously found, this gives the gelatin. 

 The peptone, etc., in the filtrate can be precipitated in the usual way. The method 

 will be of use in milk analysis for detecting adulteration with an emulsion of gelatin 

 and fat. 



The results obtained by this method were not satisfactory, and con- 

 firm the results obtained by Stutzer. All of the solutions were 

 filtered hot. The gelatin does not seem to form an insoluble formalin- 

 gelatin as described by Beckmann and the gelatin results were 

 extremely low-. In the case of meat extract and Witte's peptone, 

 some nitrogenous matter was precipitated by the formaldehyde, the 

 latter giving quite a large precipitate. When the gelatose solution 

 was used, practically no precipitate was obtained. On mixtures of 

 these various substances, either alone or in the presence of gelatin, 

 only incomplete results were obtained. 



Obermayer agrees with Kaabe'' in stating that trichloracetic acid 

 will precipitate albumin and albumin peptones and thus affords a 

 separation from other peptones, such as gelatin peptones, which are 

 only precipitated by this reagent in concentrated solution. 



The trichlor-acetic-acid method for precipitating gelatin as outlined 

 by Obermayer is briefly as follows : 



Precipitate the solution with an excess of trichlor-acetic acid, and 

 wash the precipitate with dilute sulphuric or hydrochloric acid. 

 Thoroughly extract the precipitate with alcohol, then with ether, 

 dry and weigh the precipitate. According to Obermayer, the albu- 



« Report of Thirteenth Assembly of Bavarian Chemists, 1894, pp. 18-20. 

 *>Zts. anal. Chem., 1882, 21 : 303. 



