354 PHILOSOPHICAL TRANSACTIONS. [aNNO 178/. 



soon acquires its full intensity, and is beyond comparison stronger than the 

 colour of the original trace had been. If now the corner of a bit of blotting 

 paper be carefully and dexterously applied near the letters, so as to suck up the 

 superfluous liquor, the staining of the parchment may be in great measure 

 avoided ; for it is this superfluous liquor which, absorbing part of the colouring 

 matter from the letters, becomes a dye to whatever it touches. Care must be 

 taken not to bring the blotting paper in contact with the letters, because the 

 colouring matter is soft while wet, and may be easily rubbed off. The acid I 

 have chiefly employed has been the marine ; but both the vitriolic and nitrous 

 succeed very well. They should be so far diluted as not to be in danger of cor- 

 roding the parchment, after which the degree of strength does not seem to be a 

 matter of much nicety. 



The method now commonly practised to restore old writings, is by wetting 

 them with an infusion of galls in white wine. This certainly has a great effect ; 

 but it is subject, in some degree, to the same inconvenience as the phlogisticated 

 alkali, of staining the substance on which the writing was made. Perhaps if, 

 instead of galls themselves, the peculiar acid or other matter which strikes the 

 black with iron, were separated from the simple astringent matter, for which 

 purpose 2 different processes are given by Piepenbring and by Scheele, this in- 

 convenience might be avoided. It is not improbable also that a phlogisticated 

 alkali might be prepared, better suited to this object than the common ; as by 

 rendering it as free as possible from iron, diluting it to a certain degree, or sub- 

 stituting the volatile alkali for the fixed. Experiment would most likely point 

 out many other means of improving the process described above; but in its pre- 

 sent state I hope it may be of some use, as it not only brings out a prodigious 

 body of colour on letters which were before so pale as to be almost invisible, but 

 has the further advantages over the infusion of galls, that it produces its effect 

 immediately, and can be confined to those letters only for which such assistance 

 is wanted. 



END OF THE SEVENTY-SEVENTH VOLUME OP THE ORIGINAL. 



/. Of the Methods of Manifesting the Presence, and Ascertaining the Quality, of 

 Small Quantities of Natural or Artificial Electricity. By Mr. Tib. Cavallo, 

 F. R. S. Being the Lecture founded by the late Henry Baker, Esq. F. R. S. 

 Anno 1788, Fol. 78, p. 1. 



A-fter some appropriate introductory observations, Mr. C. says that a great 

 deal still remains to be done, before we can attain to the knowledge of the object 

 in view, viz. of the real nature, of the first origin, and of the general use of elec- 



