11 



ANALYTICAL METHODS. 



In ordor to iii\ c^tiuatf the nature of tlu' i)liy>i(iil and chemical 

 chaniifcs w liicli occur in the cooking of meats, the ordinaiv methods 

 for tlie proximate analysis of foods are not sulKcient. Thus, when 

 meat is l)oiled. the uwvo (h'termination of the N\ater. protein, fat. and 

 ash in the hroth and also in the meat before and after cooking- does 

 not li'ive a sutlicient amount of infoi'ination re«,^ardinjjf the proximate 

 principles which they contain. Further, there are serious ohjections 

 to the customary preliminaiy preparation of air-dried samples, because 

 this ])rocedure produces furuhunental changes in the proteid constitu- 

 ents and undout)tedly allects to somi* extent the nature of the fats and 

 prohahlv also that of the organic extractives. The changes which air 

 (Irving brings about in tin^ proteids j)revent subsecpuMit sepaiation and 

 examination of these sul)stances. since they are for the most part, if 

 not entirely, rendered insolulde by this treatment. Since the investi- 

 gations here reported seenn'd to lu'cessitate a study of the water 

 extracts of raw and cooked meats in order to distinguish more com- 

 pletel}' between their proximate constituents, it seemed desinible to 

 analyze the fresh substance of tiie meats without tirst preparing an 

 air-dried samjile according to the usual practice. 



In former investigations" carried out in this laboratory an effort was 

 made to adapt the ordinary methods to the analysis of the fresh sub- 

 stance of both raw and cooked meats without preliminary air diying. 

 At that time the results obtained were not as satisfactory as were 

 desired. Further work has ))een done, and it is believed that the 

 various modifications here introduced in the details of the ordinary 

 method have produced more accurate results. 



In general, the method used foUow's the outline of procedure recom- 

 mended by the Association of Otticial Agricultural Chemists,'' with 

 such modifications as were described in a former bulletin of this Office,'" 

 together with further changes of details which have been found neces- 

 sary when the fresh substance of meats is used instead of the air-dried 

 material. Only these last changes need be described here. Much 

 care was taken in preparing and thoroughly mixing the samples for 

 analysis. In every case the weighings were made by difference, a 

 glass-stoppered weighing bottle being used. For the determination 

 of water the samples were weighed in glass tubes with filter- paper 

 bottoms, such as are ordinarily used in ether extraction of fat liy the 

 Johnson method.'^ In cases where the meat was rather fat, filter blocks 

 made of fat-free paper were first put into the tubes, the tubes and theii- 



a U. S. Dept. Agr., Office of Experiment Stations Bui. 102. 

 ^ U. S. Dept. Agr., Division of Chemistry Bui. 46, revised. 

 cU. S. Dept. Agr., Office of Experiment Stations Bui. 141. 

 t^Amer. Jour. Sci., 13 (1877), p. 190. 



