ALBUMINOIDS NOT DISSOLVED BY DILUTE SODA. 89 



explanation of this is to be found in the fact alluded to in § 92 et 

 seil; viz., that the material treated according to § 103 has been ex- 

 hausted with ether and alcohol previous to being extracted Avith 

 water, and that therefore the quantity of albuminoids taken 

 into solution is smaller than that extracted according to § 92. 

 But since the soluble albuminoids are determined in material that 

 has not been subjected to the action of ether, etc., it follows that 

 the nitrogen in the residue after exhaustion with water should 

 guide us in estimating the insoluble albuminoids. 



It should be observed that one extraction with dilute caustic 

 soda is often insufficient to remove all the substances soluble in 

 that menstruum. The treatment should therefore be repeated a 

 second and, if necessary, third time. 



^ 106. Albuminoids not Dissolved hij Dilute Soda. — There still 

 remains the question whether the assumption is admissible that 

 all albuminoids insoluble in water are dissolved by the dilute 

 caustic soda used in § 103. I can only reply that in a large 

 number of experiments made by Stackmann, Koroll, and Cramer- 

 DolmatofF,! the residue after extraction with water, alcohol, and 

 soda was always tested for nitrogen, with the result that in 

 none but substances very rich in suberin covdd it be said that 

 a little was often present. Of course, it would be possible 

 to apply Lassaigne's test to the residue after extraction with 

 dilute soda; if evidence of nitrogen be obtained, the amount 

 should be estimated and calculated as " albuminoids insoluble 

 in dilute soda." In experiments made by Trefther- on mosses 

 in my laboratory it was found that the amount might occasionally 

 be very considerable. At all events, if nitrogen is present, the 

 quantity should be determined. (Cf. §§ 232, 238.) 



§ 107. Substances Dissolved by Dilute Soda, not Precipitated hy 

 Alcohol. — The filtrate and washings from the precipitate obtained 

 in § 103 are evaporated to dryness, and the calculated amount of 

 acetate of soda deducted from the dried residue. (See § 237.) 

 The remainder represents the substances soluble in dilute caustic 

 soda, not precipitated by acetic acid and alcohol. If the residue 

 dissolves completely in a few cc. of water it may be concluded 

 that no substance allied to phlobaphene, soluble in alcohol, is 

 present. In that case the organic matter (apart from the acetate 



1 See the dissertations, etc., subsequently quoted. 



2 Dissertation. Dorpat, 1881. 



