7 o SCIENCE PROGRESS. 



proteose. It is not coagulated by heating to boiling" point, 

 but if the temperature be maintained at that point till the 

 solution becomes concentrated, a coagulum is gradually 

 developed. There is about "3 per cent, of this body in 

 the flour. 



The other two proteids of the flour are those to which 

 the formation of the gluten can be attributed. They both 

 show a certain resemblance to the zein described (" Science 

 Progress," vol. ii., p. 121) as occurring in the seeds of Zea 

 Mais, in that they are more or less completely soluble in 

 warm dilute alcohol. 



The first of them was described under the name of 

 gliadin by Tadder in 1820, and was referred to also by 

 Liebig under the name of plant gelatin. 



Gliadin is the proteid which is present in largest 

 quantity in the seed of wheat, about 4 per cent, of the 

 flour being composed of it. It is present also in rye. 



Its preparation is most easily effected by taking ad- 

 vantage of its solubility in hot dilute alcohol. If either 

 wheat or rye Hour, or the gluten prepared from them, be 

 treated with this solvent, the gliadin dissolves, the best 

 result being obtained by using a mixture of seventy 

 parts of absolute alcohol with thirty parts of water. 

 From this solution it is precipitated by the addition of 

 sodic chloride. When the precipitate is collected, dehy- 

 drated by absolute alcohol, and dried over strong sulphuric 

 acid, it remains as a powdery white mass. If the precipi- 

 tate is not dehydrated, but moistened with dilute alcohol or 

 water before drying, it is not powdery, but has the appear- 

 ance of gelatin, being clear and transparent. This recalls 

 the old name which Liebig originally gave to it. Cold 

 water fails to dissolve it with any ease, rendering it ex- 

 tremely viscid and sticky ; water gradually warmed has 

 more effect upon it, but even at boiling point it is not all 

 dissolved, and as the temperature subsequently falls part of 

 it separates out again. What is left in solution is partly 

 precipitated by the addition of a little sodic chloride, as is 

 the case with the original alcoholic extract. 



Gliadin dissolves readily in dilute acids or alkalies, and 



