6º. The manuscript under examination is again spread upon a glass-plate, and a solution of tannin (or preferably, a solution of ferrocyanide of potassium containing one per cent. of the salt, and acidulated with acetic acid) applied by means of a brush. If the original writing was executed with ordinary ink (which has as its base tannate of iron), and the washing has been but imperfectly performed, it is quite possible that a blue coloration will be produced by the action of the ferrocyanide. It is, however, often necessary to apply the above reagents several times before the original writing becomes apparent; indeed, in some cases months have elapsed before the reaction has occurred. In case the alteration or destruction of the document is feared in the above test, it is well to previously provide the court with a certified copy, and then proceed with the examination. 7º. If the paper possesses a friable appearance, it has possibly been washed with sulphuric acid. This property may however originate from other causes, and the presence of the acid should be confirmed by washing the document with distilled water, and adding a solution of chloride of barium to the washings. The precipitate should form in a considerable quantity, as a slight cloudiness could be due to sulphates contained in the water used in the preparation of the pulp. If much sulphuric acid be present, it may be so concentrated by heating as to cause the carbonization of the paper. 8º. It is also well, should washing with sulphuric acid be suspected, to ascertain, by aid of a lens, if the filaments on the surface of the manuscript possess an inflated appearance. This would be caused by the escape of carbonic acid, originating from the action of sulphuric acid upon the carbonates contained in the water used in the manufacture of the paper. 9º. Old ink is more difficult to remove than new, and it is therefore sometimes possible to cause the reappearance of old writings, over which words have been subsequently written. For this purpose, a solution containing 50 per cent. of oxalic acid is applied with a fine brush over the suspected points. As soon as the ink disappears, the acid is immediately removed by washing with water, and the paper dried. Upon now repeating the operation, the presence of a former writing may be detected after the complete disappearance of the words last written. 10º. According to _M. Lassaigne_, when the same ink has not been used throughout a document, washing with dilute hydrochloric acid will demonstrate the fact. This acid, while causing the gradual obliteration of characters written with ordinary ink--the shade of the paper not being altered--produces a red color, if ink containing log-wood has been employed, and a green coloration, in case the ink used contained Prussian blue.