THE PROTEIN SUBSTANCES. 21 



ent albuminous bodies, and it is, on this account, impossible to give 

 the degree of delicacy for each reaction for all albuminous bodies. 

 Of the precipitation reactions HELLER'S test (if we eliminate the 

 peptones and certain albumoses) is recommended in the first place 

 for its delicacy, though it is not the most delicate reaction, and 

 because it can be performed so easily. Among the precipitation 

 reactions, that with basic lead acetate (when carefully and exactly 

 executed) and the reactions 6, 7, 8, and 9 are the most delicate. 

 The color reactions 1 to 4 show a great delicacy in the order in 

 which they are given. 



No albumin reaction is in itself characteristic, and, therefore, in 

 testing for albumin one reaction is not sufficient, but a number of 

 precipitation and color reactions must be employed. 



For the quantitative estimation of coagulable albumin the 

 determination by boiling with acetic acid can be performed with 

 advantage since, by operating carefully, it gives exact results. The 

 precipitation by means of alcohol in the liquid which has first been 

 neutralized may also be used for this purpose. The alcohol must 

 be added so that the liquid contains 70 to 80 vols. per cent. In 

 both cases small amounts of albumin may remain in the filtrate. 

 This last may be determined by concentrating the filtrate sufficiently 

 (in the alcohol method all the alcohol must be expelled), and remov- 

 ing any separated fat by shaking with ether, and then precipitating 

 with tannic acid, with the addition of NaCl if necessary. Ap- 

 proximately 63$ of the tannic acid precipitate washed with cold 

 water and dried may be considered as albumen. The precipi- 

 tation by means of copper sulphate may also be employed as a 

 quantitative method, while the Biuret reaction may be used for the 

 quantitative calorimetric estimation of peptones and albumoses. 

 The quantitative estimation of albumin by means of the polari- 

 scope is not applicable in all cases and does not give sufficiently 

 exact results. 



The separation of albumins from a solution may, in most cases, 

 be performed by boiling with acetic acid. Small amounts of albu- 

 min which remain in the filtrates may be separated by boiling with 

 freshly-precipitated lead carbonate (HOFMEISTER) or with ferric 

 acetate (HOPPE-SEYLEE), as described in Chapter XIV on the 

 urine. If the liquid cannot be boiled, the albumin may be pre- 

 cipitated by neutral salts and acid, or by the very careful addition 

 of lead acetate, or by the addition of alcohol. If the liquid con- 

 tains substances which are precipitated by alcohol, such as glycogeu, 

 then the albumin may be separated by the alternate addition of 

 potassium-mercuric iodide and hydrochloric acid (BRUCKE). 



