436 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [4] 



in the analytical determinations have been described in the prelirni. 

 nary report* above referred to, and in less detail in the BericMe der 

 Tk'iitschen cJiemiHchen Gesellschaftj xvi, 1883, s. 1839. It will therefore 

 suffice here to j'cfer to tliem very briefly. 



Separation of edible portion {fie sh) from refuse {hones ^ slcins, entrails, 

 spaum, &c.). — The sample, as received at the laboratory, was weighed, 

 the edible portion, "flesh," was then separated from the refuse, and 

 both were weighed. There was always a slight loss in cleaning, due, 

 evidently, to evaporation and to slimy and fatty matters and small 

 fragments of the tissues that adhered to the hands and to the utensils 

 used in preparing the sample. Perfect separation of the flesh from the 

 other tissues was difficult, but the loss resulting from this v/as small, so 

 that, though the figures obtained for edible portion represent somewhat 

 less thau was actually in the sample, yet the amount thus wasted was 

 doubtless scarcely more than would be left unconsumed at an ordinary 

 table. The reasons for rejecting the skins, which generally has con- 

 siderable nutritive value, were that its chemical constitution is different 

 frt>iu that of the flesh, and that, so far as we have observed in this 

 country, it is not ordinarily eaten. With the closer domestic economy 

 that increased density of population must bring, jjeople will doubtless 

 become more careful hereafter to utilize such materials. 



Water, and water-free substance. — The material is carefully sampled 

 and partially dried at 95"^ centigrade, or thereabouts, generally in a 

 current of hydrogen, then finally ground and the drying comxfleted in 

 hydrogen. The residue, after removal of all the water, is called water- 

 free substance. 



Nitrogen, albuminoids. — The nitrogen is determined by the soda-lime 

 method. The results of a not inconsiderable amount of labor devoted 

 to the study of the conditions under which this method yields correct 

 results have been partially and briefly recapitulated in the accounts 

 above referred to. We have come to believe that with proper precau- 

 tions extremely accurate determinations may be made with soda-lime 

 but that great care is needed to insure them. 



It is customary to compute the albuminoids or protein by multiply- 

 ing the nitrogen by 6.25. In our analyses this factor has in general 

 been very nearly correct. The subject, however, demands extensive 

 discussion, for which, this is not the proper place. I have thought it 

 more to the present purpose to state the percentages of nitrogen, and 

 instead of giving the protein as calculated by multiplying these by 6.25, 

 or any other factor, to estimate the albuminoids by difference. That is 

 to say, the remainder, left after subtracting the sum of ether extract 

 and ash from the water-free substance, or the sum of water, ether 

 extract, and ash from the fresh substance, is taken as the percentage of 

 albuminoids. This is, of course, not al^solutely correct, but it is more 



* Report of the U. 8. Corainissiou ofFisli and i'isheries for 1880, Wasliingtou, ISdo. 

 Appendix D, pp. 242-248. 



