22 MEAT EXTRACTS. 



The method of Searl for the detection of yeast extract by the use of 

 a modified Fehling's solution was also tested. The method is as 

 follows : 



Prepare a modified Fehling's solution by dissolving 200 grains of copper sulphate 

 and 250 grains of neutral tartrate of sodium- in 4 ounces of water. Add to this 250 

 grains of sodium hydroxid dissolved in 4 ounces of water. Dissolve 10 grains of the 

 sample to be examined in 1.5 ounces of water, add to this one-half volume of the above 

 solution and boil for one or two minutes. With genuine meat extract no precipitate 

 is given. When yeast extract is present a curdy, bluish-white precipitate is formed. 



This method was tested on a sample of meat extract, a yeast ex- 

 tract, a 50 per cent solution of yeast and meat extract, and a solution 

 containing 20 per cent of yeast and 80 per cent of meat extract. In 

 the case of the meat extract a very fine precipitate was obtained. 

 In the three cases where yeast extract was present a flocky, bluish- 

 white precipitate was formed. It is evident from these results that 

 the presence of 20 per cent of yeast extract in meat mixtures may 

 be detected by this method. 



Searl also gives a modification to be applied when doubtful results 

 are obtained by the original method. In such cases 3 to 6 grams (50 

 to 100 grains) of the sample are dissolved in from 4 to 8 cc (1 to 2 

 drams) of water. Alcohol is added to precipitate the proteid matter, 

 the solution is thoroughly shaken, and filtered. The residue is dis- 

 solved in 45 cc (1.5 ounces) of water, filtered if necessary, and the 

 usual method applied. 



This modification was tried on 10 and 20 per cent mixtures of yeast 

 extract, but the results obtained were not satisfactory, and it is 

 doubtful if less than 20 per cent of yeast extract can be detected in 

 the presence of meat extract by this method. 



Another test is described by Wintgen, who claims that the zinc 

 sulphate filtrate in the case of meat extracts is clear, but with yeast 

 extracts it is turbid. This was found to be the case, as the following 

 results show: 



Zinc sulphate filtrate. 



A. Meat extract Clear. 



B. Yeast extract Cloudy. 



C. 50 per cent yeast and 50 per cent meat extract ( "loudy. 



D. 25 per cent yeast and 75 per cent meat extract Cloudy. 



The solutions of these extracts, or mixtures, were saturated with 

 chemically pure zinc sulphate after adding two drops of strong sul- 

 phuric acid. The solutions stood over night and the nitrates were 

 examined in the morning. The only clear filtrate obtained was that 

 from meat extract alone. 



The most important test for determining the nature of an extract, 

 whether meat or yeast, is the determination of kreatin and kreatinin. 

 This test, which has been used in the Bureau of Chemistry for two or 



« Arch. Pharm., 1904, 242:537. 



