GENERAL CHEMICAL CHARACTERS OF PROTEINS 65 



from which they can be precipitated by means of acids. Some of 

 them are, however, soluble in excess of acid. The higher bromine 

 derivatives are soluble in alcohol, but insoluble in ether, chloroform, 

 benzene and other organic solvents. They cannot be precipitated 

 from their solution in alkali by the majority of the alkaloidal reagents, 

 although they can be " salted out " by the addition of ammonium 

 sulphate. None of them have been obtained in a crystalline form. 

 They give the biuret reaction, but not the reactions of Millon or 

 Adamkiewicz (Hopkins). 



The possible reactions are very complicated, for the amount of 

 hydrochloric, hydrobromic or hydriodic acid eliminated in the re- 

 action is far larger than that which can be accounted for by the mere 

 substitution of hydrogen by halogen. Concurrent oxidation must 

 also take place. 



Some light has recently been thrown on the action of chlorine on 

 amino bodies by the researches of Raschig and of Cross, Bevan and 

 Briggs. 



Raschig has shown that chlorine and alkaline hypochlorites act 

 upon ammonia with the formation of chloramines : 



NH 3 + M'OCl = NH 2 C1 + M'OH. 



Chloramine is capable of reacting with iodides with the liberation 

 of free iodine : 



NH 2 C1 + 2HI = NH 3 + HC1 + I 2 . 



Proteins seem to undergo a similar reaction, and it is suggested 

 by Cross, Bevan and Briggs that such a reaction may serve as a 

 measure of the reactive amino groups in the protein molecule. It is 

 possible that the treatment with hypochforites in alkaline solution 

 will bring about a simple substitution, and that by means of the 

 iodide reaction the chloramine groups in the protein molecule can 

 be estimated. Evidence has already been brought to show that the 

 hypochlorite does not react to such an extent as free chlorine. It 

 is, furthermore, only the chlorine in the chloramine radical which 

 sets free iodine from combination with iodides. 1 



The action of halogens is, however, far more complex than mere 

 substitution in the sense of the chloramine reaction. Substitution 

 may take place in groups other than the amino groups. Attention 

 has been already called, furthermore, to the fact that far more of the 

 hydrogen halide is set free in the reaction than can be accounted 

 for by mere substitution. Oxidation must take place concurrently 

 with substitution. Some idea as to the reaction may be obtained by 

 the comparison of the empirical constitution of the halogen de- 

 rivative with that of the original body. Hofmeister, Kurajefif and 

 the other investigators give several analyses which throw light on 

 this point. One example will suffice, viz.> the analysis of crystallised 

 egg-albumin, and its iodo derivative as prepared by Hofmeister : 



c. H. N. i. s. o. 



Albumin 53*28 7-26 15-00 i'i8 23-28 



lodalbumin 47-92 6-60 i4'*7 8-95 1*26 21-00 



From these numbers it will be evident that in the formation of the 



1 Further research on this " chloramine factor " is necessary. A method is sug- 

 gested in the paper of Cross, Bevan and Briggs, which is, however, only of a prelimin- 

 ary character. 



