and to make it keep in, I lengthened it by adding to each end a little coat of fealing-wax.

I continued in England more than ten years, and during all that time, after the firft change, I perceived no alteration. The magnets had the fame freedom in their box, and the little fhutter continued with the added fealing-wax to fit its grooves, till fome weeks after my fecond return to America..

As I could not imagine any other caufe for this change of dimenfions in the box, when in the different countries, I concluded, firft generally, that the air of England was moifter than that of America; and this I fuppofed an effect of its being an ifland, where every wind that blew muft neceffarily pafs over fome fea before it arrived, and of courfe lick up fome vapour. I afterwards indeed doubted whether it might be just only fo far as related to the city of London, where I refided; because there are many causes of moisture in the city air, which do not exift to the same degree in the country; fuch as the brewers and dyers boiling caldrons, and the great number of pots and tea-kettles continually on the fire, fending forth abundance of vapour; and alfo the number of animals who by their breath continually increase it; to which may be added, that even the vast quantity of sea coals burnt there, do in kindling difcharge a great deal of moisture.

When I was in England, the laft time, you also made for me a little achromatic pocket telescope; the body was brafs, and it had a round cafe (I think of thin wood) covered with fhagrin. All the while I remained in England, though poffi

bly there might be fome small changes in the dimenfions of this cafe, I neither perceived nor fufpected any. There was always comfortable room for the telescope to flip in and out. But foon after I arrived in America, which was in May 1775, the cafe became too small for the inftrument, it was with much difficulty and various contrivances that I got it out, and I could never after get it in again, during my ftay there, which was eighteen months. I brought it with me to Europe, but left the cafe as ufelefs, imagining that I fhould find the continental air of France as dry as that of Pennsylvania, where my magnet-box had alfo returned a fecond time to its narrownefs, and pinched the pieces, as heretofore, obliging me too to fcrape the fealing-wax off the ends of the fhutter.

I had not been long in France, before I was surprised to find, that my box was become as large as it had always been in England, the magnets entered and came out with the fame freedom, and, when in, I could rattle them against its fides; this has continued to be the cafe without fenfible variation. My habitation is out of Paris diftant almoft a league, fo that the moist air of the city cannot be fupposed to have much effect upon the box. I am on a high dry hill in a free air, as likely to be dry as any air in France. Whence it feems probable that the air of England in general may, as well as that of London, be moister than the air of America, fince that of France is fo, and in a part fo diftant from the fea.

The greater drynefs of the air in America appears from fome other observations,

obfervations. The cabinet-work formerly fent us from London. which confifted in thin plates of fine wood glued upon fir, never would ftand with us, the vaneering, as thofe plates are called, would get loose and come off; both woods fhrinking, and their grains often crofling. they were for ever cracking and flying. And in my electrical experiments there, it was remarkable, that a mahogany table, on which my jars ftood under the prime conductor to be charged, would often be fo dry, particularly when the wind had been fome time at north-weft, which with us is a very drying wind, as to ifolate the jars, and prevent their being charged till I had formed a communication between their coatings and the earth. I had a like table in London, which I used for the fame purpofe all the time I refided there; but it was never fo dry as to refufe conducting the electricity.

Now what I would beg leave to recommend to you is, that you would recollect, if you can, the fpecies of mahogany of which you made my box, for you know there is a good deal of difference in woods that go under that name; or, if that cannot be, that you would take a number of pieces of the clofeft and finest grained mahogany that you can meet with, plane them to the thinnefs of about a line, and the width of about two inches acrofs the grain, and fix each of the pieces in fome inftrument that you can contrive, which will permit them to contract and dilate, and will fhew, in fenfible degrees, by a moveable hand upon a marked scale, the other wife lefs fenfible quantities of fuch contraction and dilatation. If these inftruments are all kept in

the fame place while making, and are graduated together while subject to the fame degrees of moisture or drynefs, I apprehend you will have to many comparable hygro→ meters, which being fent into different countries,and continued there for fome time, will find and fhow there the mean of the different drynefs and moisture of the air of those countries, and that with much less trouble than by any hygrometer hitherto in use.

With great efteem,

I am, dear Sir,

Your moft obedient, and moft humble fervant. B. FRANKLIN.

Some Obfervations on ancient Inks, with the Propofal of a new Method of recovering the Legibility of decayed Writings. By Charles Blagden, M. D. Sec, R. S. and F. A.S.

From Philofophical Transactions of the Royal Society of London.

Na converfation fome time ago

with my friend Thomas Aftle, Efq. F. R. S. and A. S. relative to the legibility of ancient MSS. a queftion arofe, whether the inks in ufe eight or ten centuries ago, and which are often found to have preferved their colour remarkably well, were made of different materials from thofe employed in later times, of which many are already become fo pale as fcarcely to be read. With a view to the decifion of this queftion, Mr. Aftle obligingly furnifhed me with feveral MSS. on parchment and vellum, from the ninth to the fifteenth centuries inclufively; fome of which were still very black, and others of different fhades of colour, from a deep yel

lowish

lowish brown to a very pale yellow, in fome parts fo faint as to be fcarcely visible. On all of thefe I made experiments with the chemical re-agents which appeared to me beft adapted to the purpose; namely, alkalies both fimple and phlogifticated, the mineral acids, and infufion of galls.

It would be tedious and fuperfluous to enter into a detail of the particular experiments; as all of them, one inftance only excepted, agreed in the general refult, to fhew, that the ink employed anciently, as far as the above-mentioned MSS. extended, was of the fame nature as the prefent; for the letters turned of a reddish or yellowish brown with alkalies, became pale, and were at length obliterated, with the dilute mineral acids, and the drop of acid liquor which had extracted a letter, changed to a deep blue or green on the addition of a drop of phlogifticated alkali; moreover, the letters acquired a deeper tinge with the infufion of galls, in fome cafes more, in others lefs. Hence it is evident, that one of the ingredients was iron, which there is no reafon to doubt was joined with the vitriolic acid; and the colour of the more perfect MSS. which in fome was a deep black, and in others a purplish black, together with the reftitution of that colour, in thofe which had loft it, by the infufion of galls, fufficiently proved that another of the ingredients was aftringent matter, which from hiftory appears to have been that of galls. No trace of a black pigment of any fort was discovered, the drop of acid, which had completely extracted a letter, appearing of an uniform pale ferrugineous colour, without an atom of black

powder, or other extraneous matter, floating in it.

As to the great durability of the more ancient inks, it feemed, from what occurred to me in these experiments, to depend very much on a better preparation of the material upon which the writing was made, namely, the parchment or vellum; the blackeft letters being generally those which had funk into it the deepeft. Some degree of effervefcence was commonly to be perceived when the acids came in contact with the furface of these old vellums. I was led, however, to fufpect, that the ancient inks contained a rather less proportion of iron than the more modern; for in general the tinge of colour, produced by the phlogifticated alkali in the acid laid upon them, feemed lefs deep; which, however, might depend in part upon the length of time they had been kept: and perhaps more gum was ufed in them, or poffibly they were washed over with fome kind of varnith, though not fuch as gave any gloss.

One of the fpecimens fent me by Mr. Aftie proved very different from the reft. It was faid to be a MS. of the fifteenth century; and the letters were those of a' full engroffing hand, angular, without any fine ftrokes, broad, and very black. On this none of the above-mentioned re-agents produced any confiderable effect; moft of them rather feemed to make the letters blacker, probably by cleaning the furface; and the acids, after hav ing been rubbed ftrongly upon the letters, did not ftrike any deeper tinge with the phlogisticated alkali. Nothing had a fenfible effect, toward obliterating these letters, but what took off part of the furface of

the

the vellum; when fmall rolls, as of a dirty matter, were to be perceived. It is therefore unqueftionable, that no iron was used in this ink; and from its refiftance to the chemical folvents, as well as a certain clotted appearance in the letters when examined clofely, and in fome places a flight degree of glofs, I have little doubt but they were formed with a compofition of a black footy or carbonaceous powder and oil, probably fomething like our prefent printers' ink, and am not without fufpicion that they were actually printed*.

Whilft I was confidering of the experiments to be made, in order to afcertain the compofition of ancient inks, it occurred to me, that perhaps one of the best methods of reftoring legibility to decayed writing might be, to join phlogiflicated alkali with the remaining calx of iron; because, as the quantity of precipitate formed by these two fubftances very much exceeds that of the iron alone, the bulk of colouring matter would thereby be greatly augmented. M. Bergman was of opinion, that the blue precipitate contains only between a fifth and a fixth part of its weight of iron; and though fubfequent experiments + tend to fhew that, in fome cafes at leaft, the proportion of iron is much greater, yet upon the whole it is certainly true, that if the iron left by the ftroke of a pen were joined to the colouring matter of phlogifticated alkali, the quantity of Pruffian blue thence refulting would be much greater than the quantity of black matter origi

nally contained in the ink depofited by the pen; though perhaps the body of colour might not be equally augmented. To bring this idea to the teft, I made a few experiments as follows.

The phlogisticated alkali was rubbed upon the bare writing, in different quantities; but in general with little effect. In a few inftances, however, it gave a bluish tinge to the letters, and increased their intenfity, probably where fomething of an acid nature had contributed to the diminution of their colour.

Reflecting that when the phlogifticated alkali forms its blue preci pitate with iron, the metal is ufually firft diffolved in an acid, I was next induced to try the effect of adding a dilute mineral acid to writing, befides the alkali. This anfwered fully to my expectations; the letters changing very speedily to a deep blue colour, of great beauty and intensity. It seems of little confequence as to the ftrength of colour obtained, whether the writing be firft wetted with the acid, and then the phlogisticated alkali be touched upon it, or whether the procefs be inverted, beginning with the alkali; but on another account, I think the latter way preferable. For the principal inconvenience which occurs in the propofed method of restoring MSS. is, that the colour frequently fpreads, and fo much blots the parchment, as to detract greatly from the legibility; now this appears to happen in a lefs degree when the alkali is put on firft, and

the

1

the dilute acid is added upon it. The method I have hitherto found to answer beft, has been to spread the alkali thin with a feather over the traces of the letter, and then to touch it gently, as early upon or over the letters as can be done, with the diluted acid, by means of a feather, or a bit of stick cut to a blunt point. Though the alkali has occafioned no fenfible change of colour, yet the moment that the ac d comes upon it, every trace of a letter turns at once to a fine blae*, which foon acquires its full intensity, and is beyond comparison ftronger 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, fo as to fuck up the fuperfluous liquor, the ftaining of the parchment may be in great measure avoided for it is this fuperfluous liquor, which, abforbing 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 foft whilft wet, and may easily be rubbed off.

The acid I have chiefly employed has been the marine; but both the vitriolic and nitrous fucceed very well. They should undoubtedly be fo far diluted as not to be in danger of corroding the parchment, after which the degree of ftrength 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 infufion of galls in white wine.+ This certainly has a great effect; but it is fubject, in fome degree, to the fame inconvenience as the phlogifticated alkali, of staining the fubftance on which the writing was made. Perhaps if, inftead of galls themselves. the peculiar acid or other matter which ftrikes the black with iron were feparated from the fimple af tringent matter, for which purpofe two different proceffes are given by Piepenbring and by Scheele, this inconvenience might be avoided. It is not improbable, likewise, that a phlogisticated alkali might be prepared, better fuited to this object than the common; as by rendering it as free as poffible from iron, diluting it to a certain degree,

Crell. Annal. 1786, B. i. p. 51.

or