A.-PREPARATION OF TAPER WITH SALTS OF SILVER. 23

Pieces of bank post paper dipped in this solution became, the instantthey were presented to the declining light of an autumnal evening, aboautiful black having a purple tinge. This effect did not seem tocome on gradually, but as by a sudden impulse, at once. Both thisgentleman and myself have often endeavoured to repeat this, butin no one instance have either of us succeeded in producing any thingnearly so sensitive. It should bo stated, that the solution prepared inthe evening, had become, by tlio following morning, only ordinarilysensitive, and that papers prepared with it were deliquescent and bad.In repeating any modification of this experiment, the greatest careshould be taken, as explosions of considerable violence are otherwisolikely to occur.

Another sorics of experiments on the fulminates of silver havo pro-duced very pleasing photographic results, but I am not enabled tospecify any particular method of preparing them, which may be certainof reproducing the results to which I allude. Nothing can be morocapricious than they are: the same salt darkening rapidly to-day, whichwill to-morrow appear to be absolutely insensible to radiation, and whichwill again, in a few days, recover its sensitiveness, to lose it as speedilyas before.

Tlieso notices will show the immense field of inquiry which photo-graphy has opened up, as fertile as it is oxtonsivo, in which everyinquirer may be assured of tlio reward of discoveries of interest toscience, and of importance to the arts.

ff. Dr. ScnAFnAEUTL’s Negative Process.

At the tenth meeting of tlio British Association for the Advancementof Science, two new processes on paper, and one on metal, were broughtforward by Dr. Scliafhaeutl. Tlieso processes involve some very deli-cate manipulatory details, which render them very tedious, and, in tliohands of the inexperienced, uncertain. However, as they sometimesgivo very perfect results, it would havo been improper to have omittedthem.

Penny’s improved patent metallic paper is recommended. This isspread with a concentrated solution of the nitrate of silver, (140 grains to2 \ drachms of fused nitrate, to G fluid drachms of distilled water,) bymerely drawing tlio paper over the surface of the solution contained ina largo dish. In order to convert this nitrate into a chloride, thoauthor exposed it to tho vapours of boiling muriatic acid. A coatingof a chloride of silver, shining with a peculiar silky lustre, was by thismothod generated on the surfaco of the paper, without penetrating intoits mass; and in order to givo to this coating of chloride the highestdegreo of sensibility, it was dried, and then drawn over tho surface ofthe solution of nitrate of silver again. After having been dried, thopaper was ready for use, and no repetition of this treatment was able toimprove its sensitiveness.

Even on the ordinary kinds of writing paper, I have found this