CHEMICAL CHANGES OCCURRING IN OYSTERS. 7 



posed at the end of the week. In this lot, the values for both amino- 

 acid and ammoniacal nitrogen were smaller at the end than they were 

 at the beginning of the experiment. 



Of the two determinations intended to show the amount of de- 

 composition which has occurred in oysters, it appears that deter- 

 mination of ammoniacal nitrogen by the Folin method is worthless 

 in commercial oyster work for the following reasons : 

 (a) The free ammonia and ammonium salts are washed out of the 



oysters nearly as fast as they form. 

 (6) The very small amount of standard acid neutralized by the am- 

 monia makes the probable error relatively large. 

 (c) With alizarin red as an indicator, the color change obtained is 

 not sharp, under such conditions. 



For the last two reasons, duplicate determinations often varied 

 widely, and no great reliance is to be placed upon the accuracy of 

 the determinations; hence, very little weight should be attached to 

 the meaning of the results obtained. Often higher ammoniacal 

 nitrogen figures were obtained from fresh oysters than from others 

 which had undergone decomposition. 



It is believed that the amino-acid nitrogen determination is much 

 more consistent and reliable. It is more consistent in that a larger 

 amount of solution is taken for titration, which lessens the probable 

 error, and in that the end point is easier to locate. The principal 

 objection to this determination is that the amino-acid nitrogen con- 

 tent is not a true indication of the amount of decomposition which 

 has taken place in the oysters, for the following reasons: 



(a) Amino acids, being soluble, are washed out of the oysters by 



each change of water in the same way as are the ammonia 

 and its compounds. 



(b) Amino acids present a very suitable medium for bacteriological 



growth, and are, therefore, being continuously broken down 

 into some of the simpler compounds already mentioned. 

 Therefore, the amount of amino acids present is never a 

 measure of the total amount of decomposition, and in many 

 cases is a measure of only a very small percentage of it. 

 However, the results obtained on oysters undergoing wash- 

 ing treatments are comparable, and are of great value in 

 indicating the amount of soluble matter removed. 

 In the study of washing oysters, the greatest reliance is to be 

 placed upon the determinations for amino-acid nitrogen, total solids, 

 and ash. The figures for moisture are very useful in showing the 

 amount of water added to the oysters in the washing processes. 

 The determinations for salinity were of little assistance, as the salt 

 was removed quite completely in a comparatively brief period of 

 washing. 



