56 THE PROTEINS. [CH. II. 



filtrate with twice its volume of 40 per cent, sodium hydroxide and a 

 drop of i per cent, copper sulphate. A pink colour appears, due to 

 the presence of peptone. 



Important Note. This large excess of strong NaOH must be added in 

 order to decompose the (NH 4 ) 2 SO 4 with which the solution is saturated. The 

 characteristic rose colour is only obtained when the alkalinity is due to NaOH, 

 ammonia being quite inefficient. 



5 cc. of saturated (NH 4 ) 2 SO 4 solution contains about 3-75 grms. of the salt. 

 This requires 2-27 grms. of NaOH. 10 cc. of 40 per cent. NaOH, containing 

 4 grms. of NaOH, is thus sufficient. 



58. Evaporate a small portion of the original fluid to complete 

 dryness, finishing the process on a water bath in order to prevent 

 charring. Rub up the residue with successive small quantities of 

 strong alcohol (95 per cent.). Add the extracts together, filter and 

 evaporate them to dryness on a water bath. Dissolve the residue 

 from this evaporation in a little water and test for proteins by the 

 various colour tests. Only insignificant traces are present, showing 

 that albumoses and peptones are insoluble in strong alcohol. 



NOTE. It is frequently desirable to remove all proteins from a solution 

 before testing for certain substances, e.g. sugars, bile-salts, urea, etc. In the 

 case of albumoses and peptones this can only be effected by the method 

 described above, advantage being taken of the solubility of sugars, etc., in 

 alcohol, and the insolubility of all proteins in the same. The aqueous solution 

 prepared in this way will be spoken of as " an alcoholic extract." 



Peptones. Use a 2 per cent, solution of Savory and 

 Moore's peptone, which is usually free from albumoses. 



59. Apply the usual colour reactions for proteins. They are 

 all obtained. 



NOTE. The glyoxylic reaction may not be very intense, owing to the 

 presence of chlorides in the preparation. Pure peptone, when freed from 

 chloride by appropriate means, gives a very good glyoxylic reaction. 



60. Add a drop or two of strong acetic acid and a drop of 

 potassium ferrocyanide. No precipitate is produced, showing that 

 the primary albumoses are absent. 



61. Add a little Esbach's or Briicke's solution. A very slight 

 or no precipitate is formed, if the solution be free from albumoses. 



62. Saturate a portion with ammonium sulphate. No precipi- 

 tate, or only a slight one, is produced, showing that albumoses are 

 absent. 



