barium. With very dilute solutions traces of these compounds may escape detection. During the concentration of the solution, that of the sulphuric acid and barium hydroxide naturally increases, so that we may eventually get an hydrolysis of the peptone mixture.
Finally, we are left with a light yellow syrupy residuum. The latter is mixed with about 100 times its amount of methyl-alcohol, and the mixture is boiled. The boiling hot solution is filtered through a filter paper into about five times its amount of cold ethyl alcohol. It is well to put the latter into iced water. Precipitation is aided by the addition of ether. The whole is filtered, directly the precipitate begins to be formed. During the filtration, the filter should not be allowed to become empty. It is best to use a filter pump. Only at the end is the liquid allowed to pass entirely through the filter, after which the latter is immediately placed in a vacuum exsiccator. After a day or two the peptone is absolutely dry, and may then be weighed. First, a 10 per cent. solution, in 0.9 per cent. solution of common salt, is prepared, and the deviation of rotation of the solution is determined. If this is more than 1°, the solution is diluted, until it shows a rotation of about 0.75°. The higher degree of rotation would not be injurious. Dilution is only effected in order to make the best use of the costly material.
