BASIC AND ACID PROPERTIES OF PROTEINS 23 



and the fact that the edestin has precipitated in combination with the 

 acid is conclusively shown by the behaviour of this precipitate. When 

 such a precipitate is washed thoroughly with dilute alcohol, until all 

 the sodium chloride is removed, and is then dissolved in water, a definite 

 quantity of potassium hydroxide is required to render the solution 

 neutral to phenolphthalein. When thus neutralised, the edestin is 

 completely precipitated, and can be removed from the solution by filtra- 

 tion. If this solution is then evaporated to dryness it leaves a residue 

 of potassium chloride containing nearly all of the alkali originally em- 

 ployed for neutralisation. It seems clear from this experiment that the 

 hydrochloric acid used to dissolve the edestin is precipitated with it in 

 the form of a protein salt. 



If edestin is extracted from hemp-seed by means of a sodium 

 chloride solution the extract has a slightly acid reaction toward litmus. 

 If this extract is dialysed the edestin is precipitated in a crystalline 

 form, and, when washed with water and alcohol and dried, can be ob- 

 tained as a powder composed of microscopic crystals. If this powder 

 is suspended in water, as can be very easily done, owing to its physical 

 condition, a certain quantity of potassium hydrate must be added to the 

 suspension before a red colour is produced with phenolphthalein. The 

 edestin then remains as an insoluble mass of decomposed crystals. 

 The solution filtered from this, when evaporated to dryness, leaves a 

 residue of potassium salts of various acids, the greater part of which 

 consists of potassium chloride, but together with this is a small quantity 

 of sulphate and of phosphate and also a small quantity of organic salts 

 of potassium. 



This is illustrated by the following experiment in which 75 grammes 

 of very carefully washed edestin were suspended in pure water and 

 made neutral to phenolphthalein with 90 c.c. of decinormal potassium 

 hydrate solution, diluted with much water and added gradually. After 

 the mixture was shaken in a closed flask for some hours the undissolved 

 edestin was filtered out and thoroughly washed. The filtrate and 

 washings yielded a residue which, dried at 1 10, weighed 0*6700 gramme. 

 After ignition 0*5433 gramme of inorganic matter remained, which 

 analysis showed to have the following composition : 



Per cent. 



Potassium carbonate . ... . . . . . . . 18-40 



Potassium sulphate .... . * . . . . . 17-81 



Potassium chloride . . . . 5i'54 



Potassium phosphate . . 4-32 



Sodium chloride 1*67 



Undetermined and loss 6-26 



xoo'oo 



