170 METHOD OF COPYING PAINTINGS UPON GLASS. 



but is lefs (o- The nitrate, however, from its folubility in water, poflbfles 

 lublc. an advantage over the muriate : though leather or paper may, 



without much difficulty, be impregnated with this laft fub- 

 ftance, either by diffufing it through water, and applying it in 

 this form, or by imraerfing paper moiftened with the folution 

 of the nitrate in very diluted muriatic acid. 

 taution. Yo thofe perfons not acquainted with the properties of the 



falts containing oxide of filver, it may be ufeful to ftate, that 

 they produce a flain of fome permanence, even when mo- 

 mentarily applied to the Ikin, and in employing them for moif- 

 tening paper or leather, it is necelfary to ufe a pencil of hair, 

 or a brum. 

 Something like a From the impoffibility of removing, by warning, the colour- 

 ma v perhaps 'be m g matter of the falts from the parts of the furface of the copy 

 efte&ed here, which have not been expofed to light, it is probable that, both 

 in the cafe of the nitrate and muriate of filver, a portion of the 

 metallic oxide abandons its acid to enter into union with the 

 animal or vegetable fubftance, fo as to form with it an infoluble 

 compound. And, fuppofing that this happens, it is not im- 

 probable but that fubftances may be found capable of deftroy- 

 ing this compound, either by fimple or complicated affinities. 

 Some experiments on this fubject have been imagined, and an 

 account of the refults of them may poffibly appear in a future 

 number of the Journals. Nothing but a method of preventing 

 the unfhaded parts of the delineation from being coloured by 

 expofure to the day is wanting, to render the procefs as ufeful 

 as it is elegant. 



VII. Obftrvatiom 



