Page:Defensive Ferments of the Animal Organism (3rd edition).djvu/231

 precipitate, either with barium hydroxide solution or with sulphuric acid. In the test with barium hydroxide it may happen, that a precipitate appears, even though no more sulphuric acid is present. These are barium salts of peptones, which separate out. They can be dissolved in nitric acid, while barium sulphate is insoluble in this.

Neutralization is carried out in such a way, as to calculate the quantity of barium hydroxide necessary, by the amount of sulphuric acid used. The barium hydroxide is best added in the solid form, and is well stirred until the action is complete. The neutralization of the sulphuric acid is first tested by means of litmus paper. Finally, small samples are filtered through a small funnel, and then one sample is tested with barium hydroxide, and another with sulphuric acid. If, in the first case, the solution becomes turbid, or precipitates are formed, then nitric acid is added, and the solution is slightly warmed.